The outside of a motorbike engine seen up close near the exhaust

Home Repair And Restoration

CBF 125 Injector Explained

Explanation Date 13-3-2015

By Ren Withnell

the inside of the injector system and throttle body on my cbf 125
Petrol...meet air...

The UK Honda CBF 125 is fuel injected. I have been told that in other countries such as India this model comes with a carburettor as this is better understood and easier to fix by the locals. Here in the wealthy UK we apparently prefer to pay a small fortune to a mechanic in a shiny workshop to replace things rather than fix them ourselves. Oh, and something to do with emissions? Are emissions a problem on a 100mpg plus motorcycle? Oh well.

In fact once you understand how the fuel injector works in many ways it's actually simpler than a carburettor. While few of the actual components are repairable by a human being they are quite easily replaced. The biggest issue is working out which part to replace. Here I'll give a simple explanation as to what each part is and what it does.

The Whole Unit.

the complete throttle body off a honda cbf 125
The entire injector unit or throttle body

The throttle body sits between the engine and the air box. Once the high pressure fuel pipe, throttle cable, clamps and 3 electrical connectors have been removed the whole unit comes out of the bike quite easily. It is a small compact unit and of a simple design. It's basically a tube with some bits on.

Sensor Unit.

The sensor unit is the "black box" marked "9929A" above. Within this box are the electrical bits that you can't fix yourself. Inside are the throttle position sensor (TPS), intake air temperature sensor (IAT) and manifild absolute pressure sensor (MAP). 

  • Throttle Position Sensor - this allows the ECU (engine control unit, a computer that runs the engine) to know how much you've turned the throttle aka accelerator. It needs to know so it can let more or less fuel through the injector depending on what you're doing.
  • Intake Air Temperature - this tells the computer how warm or cold the air is coming into the engine. Air temperature effects how much fuel the engine needs to run correctly.
  • Manifold Absolute Pressure - this tells the computer how hard the engine is sucking! As in sucking in air. This also helps the computer decide how much fuel to let through the injector.

So this box has 3 sensors which feed information to the computer or ECU. Along with engine temperature, engine revs and the Lambda sensor the computer uses it's program to alter the amount of fuel allowed through the injector. 

the sensor unit removed from the throttle body
The sensor unit removed from the throttle body. 3 "Torx" bolts. 

Idle Air Control Valve.

The air idle control valve is fitted to the opposite side of the throttle body to the sensor unit. Within the throttle body casting is cut a complex tube that allows a small amount of air to bypass the butterfly valve. This is the tickover system in a similar manner to that of a traditional carburettor. The IACV is actually a small motor and threaded pin. As the motor turns the pin the threads move a piece of plastic in and out. This gradually opens or closes the airway allowing more or less air through. By altering the amount of air passing through the airway and altering the amount of fuel the injector pumps into the engine the computer can manage the tickover.

the hole that leads to the tickover or idle passage
The hole on the left is the start of the tickover airway.
the idle air control valve. A small plastic motor with a plastic plunger
The Idle Air Control Valve. The slotted plastic part moves along the pin, opening or closing the airway.

The Injector.

The injector is the most important part and yet seems to be the smallest and most innocuous. At the top of the throttle body it is held in place by 2 8mm bolts and a piece of plastic that the high pressure hose connects to. There's no special clamps just a few rubber seals. You can't get inside the injector itself but I presume there's a simple tiny solenoid that opens and closes rapidly. As fuel is pumped at quite high pressure by the fuel pump it flows to the injector. The solenoid opens and allows a microscopic droplet of fuel past. This fuel at high pressure squirts through the tiny holes and evaporates into the air being sucked into the engine, ready to burn in the piston.

There's an electrical connector on top of the injector to operate the solenoid. This is connected to the computer which controls how fast the solenoid opens and closes, this controls how much fuel is mixed into the air.

the injector unit itself and a close up of the tiny holes where fuel is injected
The injector unit, and the tiny teeny holes where the fuel squirts through.

And that's it! The advantage over a carburettor is the computer control. Engines need different amounts of fuel for many many different situations. Cold weather, warm weather, high altitude, high speeds, low speeds, warm engine, cold engine, full throttle, tickover...the list goes on and on. Carburettors can be very simple and "cope" with a range of needs but there is always a compromise.

In the search for efficiency and perfect running carbs got very complex. Diaphragms, accelerator pumps, various ports or venturis and automatic chokes. Modern injection systems can be much simpler and all the variations taken into account by the computer program. Rather than making a complex carb you write a complex program for a simple injector.

Price.

Of course most of these parts can not be fixed by home mechanics, mind you it's rare to be able to fix carb parts either. The following is a list of prices from a Honda parts website to give you an idea of replacement costs on the CBF 125

  • Sensor Unit - £107
  • Idle Air Control Valve - £50
  • Injector Unit - £50
  • Entire Throttle Body (Includes Everything) - £340

I hope this is useful!

Reader's Comments

Alex said :-
Great work buddy!
01/01/2000 12:00:00 UTC
Ren - The Ed said :-
We try our best. Cheers Alex.
01/01/2000 12:00:00 UTC
Myles said :-
Very interesting and well written article, I am currently experiencing a slightly rough idle (consistent speed but slightly odd rythmn) on my cbf so may attempt cleaning some of these parts. Thanks for posting!
01/01/2000 12:00:00 UTC
Ren - The Ed said :-
Hi Myles. Be sure to check your tappets. This is primarily a cold starting problem but it won't do any harm to check them. Check out these 2 pages...

http://bikesandtravels.com/biker.aspx?ride=488
http://bikesandtravels.com/biker.aspx?ride=711

Also be aware of the spark plug cap breaking down...

http://bikesandtravels.com/biker.aspx?ride=747

I'd also stick in a new spark plug as a matter of routine before messing with the injector. Basically start with a good service including air filter and a thorough look at all the pipes, wires, tubes etc to ensure everything is connected properly.

If all that fails and you clean all the parts and still get no positive outcome then I would suggest looking on Ebay. The CBF 125 sold in fleets and as the injector wouldn't normally be damaged in a crash there are lots out there for very cheap prices.

I'd love to hear how you get on.

01/01/2000 12:00:00 UTC
Myles said :-
Thanks for those links. I will start with a full service as suggested. Will post back the results!
01/01/2000 12:00:00 UTC
Dest said :-
Awesome info buddy, clear as water.... Thanks
18/03/2017 06:26:39 UTC
Ren - The Ed said :-
Cheers Dest. They're not as complex as I first thought.
18/03/2017 11:03:35 UTC
Curtis Shields said :-
I have replaced the fuel pump, injector, spark plug. battery seems strong. I also changed fuel line. The bike won't stay running. It just dies randomly. Seems worse when warm. It has a hard time maintaining a consistent rpm.
26/04/2018 05:22:24 UTC
Ren - The Ed said :-
Air Idle Control Valve??

Before you look at that do ensure the tappets are set correctly. Normally this affects cold running but it's best to ensure everything else is right. Once you've checked the valve do a compression test too - both cold and warm. If the valves are good and the compression is good then go back to electrics and fuel.
26/04/2018 07:40:16 UTC
Ronan smith said :-
My bike was away for 3 weeks in a lock up just as the snow and ice passed over Scotland and didnt really need it too much. I went to get it out yesterday and my throttle started to stick. I checked the adjustment of my bar end to make sure it wasnt holding it open, nope. I traced it back to throttle body and noticed that it was sticking just before it closed wouldnt snap back into place when releasing to change gears. Any ideas of what could be the problem and what to do?
06/02/2019 08:59:24 UTC
Ren - The Ed said :-
Well the very first thing you need to do is be blooming careful! You do not want the throttle sticking open. Even a low powered 125 will be blooming lethal mid corner with the throttle stuck on. Unfortunately this model has no kill switch so you can't rapidly knock off the motor from the handlbars. Gosh only knows why it has not got one.

Typically the most likely candidate will be the throttle cable. Remove it from the bike and inspect both ends very closely. ANY loose or frayed cable strand and replace it immediately. ANY stiffness replace it immediately. They're cheap, a genuine Honda one will only cost £13. For that price I'd just change it anyhow.

With the cable removed does the throttle body snap shut as it should? Then it's the cable. If not I'd clean the throttle body, particularly around the spring and cam where the cable connects. Lube it too. If that doesn't cure it unless you're an experienced mechanic I'd be seeking the help of a good quality mechanic. Personally I'd feel comfortable taking the body apart but if you get it wrong it could be costly or even potentially dangerous.

I still think it'll be the cable and for the price - fit a new one.
06/02/2019 09:12:43 UTC
Ren - The Ed said :-
A link to Lings Honda Parts. They use the same price as most Honda dealers so if they're charging more they're ripping you off.
https://www.lingshondaparts.com/partscatalog/catalog/listing/catalog/hondamc/cat...
06/02/2019 09:14:21 UTC
Ronan said :-
Hi Ed, Thanks for the ideas! I got a new throttle cable but sadly it didnt help. I did however decide to strip the full unit, which was a lot easier than i thought it would be. After about half an hour using degreaser, then alcohol and some muc off protectant oil my throttle body is snappier than when i got the bike.
14/02/2019 09:05:29 UTC
Sridhar Sahoo said :-
Hey,
What are the sensor pin configuration of the throttle body sensor attached to it ?
04/03/2019 06:05:57 UTC
Ren - The Ed said :-
Hi Sridhar Sahoo. I'm afraid I wouldn't know that. I'm not sure where you'd find that information too, perhaps you'd need a Honda workshop manual.
04/03/2019 07:50:18 UTC
Norman said :-
My cbf cuts out when I try to rev from cold but it's ok if left to idle for 5 mins, any ideas.
16/03/2019 11:41:58 UTC
Ren - The Ed said :-
Hi Norman. IF IF it ticks over solidly but dies if you twist the throttle I doubt it's the valves - but as a matter of good practice check the valve gaps anyhow. Again good practice to fit a fresh air filter and spark plug too.

Listen and look on a dark night for the spark plug cap arcing out - I've had problems with mine.

Is the an engine check light on? It could be the temperature sensor not sending temperature to the computer so it would short fuel for the cold temps. Could possibly be a sticking air idle control valve.
16/03/2019 09:17:43 UTC
Dave Perrin said :-
It's about my sons cbf125 on his way to work he suddenly lost revs he nocked it down a gear and it seemed to pick up then he lost revs completely and the engine died I think that the injector has packed up. Is there any way of checking it with a multimeter? I'm old school so if it was a carburetor I would be able to sort it but with fuel injection I don't have a clue thanks for your help
10/11/2019 02:55:56 UTC
Ren - The Ed¹ said :-
A quick internet search tells me a genuine honda injector from your local dealer will cost about £62.

Start with the compression? Has it got any?
Check for a spark, it there one?
Only when they are confirmed good check the fuel pump - remove high pressure pipe to injector then switch on ignition - the pump should come on for 5 seconds - NOTE! - no naked flames or hot things, be ready with a container to catch the fuel.

I'm finding used CBF125 throttle bodies off Ebay for £15. This includes the injector and the sensor pack. At this price you don't fix injectors, you replace them.

11/11/2019 09:14:54 UTC
Jon C said :-
Thanks for the article . Absolutely excellent explanation of the injector.
I have a question. Bike broke down a while ago and I found fuel in the oil and scoring in the bore. I bought a piston kit and the bike is running again. However, today I noticed fuel in the oil again. Do you think that a leaking inlet valve would cause this contamination? The fuel injector was swapped out when I changed the piston . Thanks for your advice in advance!
22/05/2020 02:09:53 UTC
Bogger said :-
It'll not be the inlet valve 'leaking' or not sealing properly. Probably and electrical fault keeping the the injector open for a period once the engine has been switched off.
An easy check might be to go for a spin on the bike and get it up to temperature. Then immediately remove the injector and see if there are any leaks/dribbles.
You could put the injector into a plastic cup of some sort to catch any fuel that may leak. Obviously the injector fuel line is still connected to the injector during this process. Check every 5mins or so otherwise any fuel will evaporate.
I don't think it will be an over fueling issue either. The bike would run very very badly if at all and fuel consumption would be through the roof.


Bogger
22/05/2020 07:11:13 UTC
Ren - The Ed¹ said :-
First off Jon C - what is your bike? I'm guessing a CBF125 but not necessarily.

Until we know the bike the only logical possible route from the fuel tank to the engine would be through the injector. I agree with Bogger, fuel still being pumped momentarily after being switched off or injector leaking under even gravity pressure from the tank. I was thinking overfueling but with enough fuel for unburned fuel to get into the oil it would run like a dog.
22/05/2020 09:02:36 UTC
Upt'North said :-
I'm thinking and typing at the same time so this will probably be nonsense, what's new.
Can you remove the injector and reconnect the lead and fuel supply then turn on the power. I'm guessing at this stage the pump will prime the manifold injector, I think it'll run at about 50 psi. Have a deep clear jug to put the injector in and in a well ventilated area. Put your fag out too.
I'm now guessing no fuel should be leaving the injector. I suspect it is and I suspect the injector is buggered. If no fuel leaks try to start the bike and I'm now guessing fuel will spray inside the jug. Does it stop when you stop cranking the engine. Does it stay dry under the residual fuel line pressure which will stay up for a while.
All this assumes the electrical system will allow you to do this when the injector is removed, I think this simple system probably would.
Report back Amigo.
Upt'North.
22/05/2020 09:52:18 UTC
Ren - The Ed¹ said :-
With a CBF125 you can remove the high pressure pipe to the injector and switch on the ignition. The pump will run for 2 seconds I think. Once the pump stops the flow SHOULD stop... I did this once when testing for fuel flow, there's a guide in the Haynes manual.

Logically if the injector is removed and visible (and reconnected to the high pressure fuel pipe) when the bike is cranked via the starter button it should inject fuel (otherwise how would it start). Again once the starter is released the injector should stop without further leaking.

It's worth noting a whole used throttle body off a CBF125 is relatively cheap (£20-£30) off ebay. They are a common bike and these parts don't get smashed in a crash.
22/05/2020 10:17:56 UTC
Jon C said :-
Hello everyone ,
Thank you for your advice! Yes it’s a cbf125 2012. It’s done 16,000 miles. So to recap. A leaking inlet valve would not cause this. So it’s not worth taking the top of the engine off to check?
There could however be something wrong with the injector Or throttle body where the amount of fuel being delivered is greater than it should be. I should say that when I piston kit I also swapped out the injector for one I got off e bay.
This afternoon I’ll Drain the oil and look at the level. I’ve literally only done 11 miles since putting the engine back together again, so for the fuel to have reached the oil in such a short time, whatever the leak is, must be bad. I’ll put fresh oil in and do the injector tests you guys suggested to see if it’s dripping. When throttle is not being applied.
22/05/2020 11:01:09 UTC
Upt'North said :-
The inlet valve would not cause this issue.
Upt'North.
22/05/2020 12:57:17 UTC
Ren - The Ed¹ said :-
Think we need to clarify things. Jon C you obviously have some mechanical skills as to change a barrel and piston is no mean feat. When you talk of the inlet valve are you talking of the poppet valve in the cylinder head that lets the air/fuel into the piston/barrel/combustion chamber? I cannot conceive of a way an inlet valve could cause the problem you see so I'm double checking with you.

If there were to be fuel at the inlet valve that fuel most definitely should not be there! The only fuel reaching the inlet valve should be a fine mist, more like a vapour, mixed with air ready to be burned as the engine is running.

So if there fuel is reaching the inlet valve in a liquidy wet sort of way it's not the inlet's fault. You'd ask why there is wet fuel there when there should be none, when the motor is not running. Subject to something being WAY off the only fuel part nearby is the injector. Hence why we're pointing at the injector.

I'm just double checking our idea and your idea of the inlet valve are the same.
22/05/2020 01:39:44 UTC
Jon C said :-
Ren,
Yes that is indeed what I was wondering. I could not imagine that such a huge build up of fuel Outside of the inlet valve would be normal. I’ll drain the oil today. Put fresh stuff in. And see what happens to the injector by doing several of the suggested tests. One thing I should mention is that I did swap out the injector but not the throttle body. So I like the idea that this is such a cheap part that I should just change the whole thing anyway.
Thanks again everyone, much appreciated. If interested I’ll Keep you posted on what I find?
22/05/2020 02:33:29 UTC
Jon C said :-
Ok. Drained the oil. Stank of fuel. But level wasn’t stupid (800 ml).
Removed the 2x 8mm boots holding the injector in place, took it out and put it into a cup.
Turned the ignition to on position and saw a jolt as the pressure built in the fuel line. No leak from the injector. I pushed the starter and the injector started spraying. When I let go, it stopped and I took a new cup and left the key on the on position to keep the fuel line pressure on. Absolutely nothing. The injector is not leaking. Any ideas?
The oil was very dark after only 11 miles and it reeked of fuel.
Let me ask you this. When I was pressure testing the engine I got about 140 psi. Is this ok? Haynes said that it should be 180 psi. Most people I’ve spoken to are happy with 140 psi. But for a new barrel and with good valve seals should this actually be nearer 180 psi?
22/05/2020 06:21:46 UTC
ROD said :-
Hi, Just thought I would add my thoughts.

As already mentioned if the injector is working correctly it will deliver a fine mist of fuel air mixture to the engine.
If however the fuel is passing through the injector when the engine is not running and the inlet valve is in the open position this may pass the now cold piston and rings and enter the oil system at the crank.
The pistons and rings should be in good condition as this is a new barrel and piston kit, and if the above leak through occurs it should result in a build up above the piston and lock the engine on the compression stroke, so if you have access to a compression tester it may be worth checking the pressure in the cylinder.

So the problem no matter where the petrol finds its way to the oil, points back to the injector/throttle body allowing fuel past in some way.
22/05/2020 06:26:03 UTC
Bogger said :-
Compression at 140 is fine IMO. I'd just worry about fuel in the oil for now.

Bogger
22/05/2020 08:23:28 UTC
Ren - The Ed¹ said :-
Curiouser and curiouser...

ROD - no piston is totally sealed. If I were to put fuel into even a sparkly new engine's combustion chamber I'd expect it to drain down past the rings slowly but surely.

Jon C - 140 psi is fine. Firstly with new rings and barrel it'll take some time for them to bed in. Secondly unless you have a top quality gauge they're not particularly accurate. Thirdly my 89,200 mile CBF125 gives me about 80psi on the gauge and it still works (mostly).

The oil being dark wouldn't worry me. You don't get ALL the oil out on a change and it only takes a little of the old oil to make it look dirty.

It sounds to me like you've tested all I can think of. Maybe leave the injector off overnight to see if anything dribbles out? Run the bike for a good ride then remove the throttle body, see if anything happens after a long run? Repeat the experiment to make sure it's not random?

Otherwise I'm trying to think completely out of the box. Let's go completely mad. There's a breather out of the tank, that's not routed to the engine breather? The engine breather (under the throttle body) should run to the base of the airbox behind the fuel pump. Fuel getting into the airbox then to the breather then to the oil? Look for signs of petrol in the airbox.
22/05/2020 08:35:03 UTC
Jon C said :-
I thought I’d mention this in case you guys suddenly spot a clue that I have missed.
When I try to start the engine from cold in the morning in order to get it going, I have to Open the throttle. Otherwise the engine will turn over but will splatter to a stop.
That is the only thing that is slightly odd. I thought it was just an issue of idling speed maybe. Nothing more.
Ren, I can absolutely check the air box. I’m prepared to check everything. It’s got fresh oil now. 89,000 miles! Mate! I wish! Incredible.
22/05/2020 10:10:42 UTC
Ren - The Ed said :-
Tappets.

Weird starting and many idle issues are related to tappets being out. It is, perhaps... just possible, maybe clutching at straws, but if the tappets are wrong it might confuse the computer causing over fuelling. Doubtful but checking the tappets can't do any harm.
22/05/2020 10:43:48 UTC
Ren - The Ed said :-
Also double check the timing chain alignment, could you be a tooth out?
22/05/2020 10:45:01 UTC
Jon C said :-
One thing that I’ve learned to never ever rule out is human error. I’ll check with feeler gauges tomorrow and also timing chain position. I was ultra careful as I realised that bad timing would ruin my engine but never say never.
22/05/2020 11:04:05 UTC
Ren - The Ed¹ said :-
It's difficult online when someone asks for help simply because I have zero knowledge of your knowledge. You could be a top flight spanner wizard with a peculiar issue you just can't see (it happens to us all) or a buffoon with zero understanding of the infernal combustion engine and a big hammer. I'm getting the impression you know your way around an engine which makes life easier.

Carry on chief! Let us know how you get on.
23/05/2020 09:14:48 UTC
Jon C said :-
Hello Ren!
Are my a baboon with a spanner? Maybe! I’m a lab scientist who tinkers. Not a mechanic but someone whose job is to develop and write protocols. I have a natural born need to Understand how and why things work or don’t . When away from work I’m always either restoring bicycles, building 3D printers, fixing the car etc.
The failure: I was doing 60 mph on the A10, when I had a sudden loss of power. And my instinct was significant loss of compression. During lockdown I decided that my mechanic’s offer of £300 to take my 16,000 mile, 2012 damaged bike off me was a bit crap, and that I would learn how to open up the top end of an engine. Bought a Haynes manual and watched hours of YouTube Videos . Everyone was telling me that the cbf125 was such an easy bike to work on and learn from, that I decided to try. To my surprise, taking the engine out on a cbf125 was easy. The piston was damaged , there were scoring marks on one side of the barrel (piston picture included). Fuel had mixed with my oil, which I was guessing was due to piston ring failure. Bought a new piston kit and also a replacement fuel injector . Compression looked good and the bike runs smooth. Except On start up when I need to give it gas. Fuel smell in the oil again, part of me wants to think that maybe I hadn’t flushed the engine sufficiently but the odour is strong. Worst case scenario, I could buy another engine block. But I really do need to understand wtf is causing this. I was really careful with valve clearances and timing when putting the engine back together. But as stated before, I’m experienced enough to know that one should never rule out human error. There, you’re up to date!
Posted Image
23/05/2020 01:02:54 UTC
Upt'North said :-
That piston is ugly but the petroleum spirit did a lovely job cleaning out the crankcase. Every cloud.........
Upt'North.
23/05/2020 02:20:21 UTC
ROD said :-
After experiencing a similar piston/barrel problem when riding a 250 Suzuki into a head wind on the M6 I developed my dislike of riding near to the limits of the bike.
23/05/2020 02:37:16 UTC
Ren - The Ed¹ said :-
It'll scrub up that piston with a bit of JBWeld as required.
23/05/2020 04:48:54 UTC
Upt'North said :-
Jon,
This is a conundrum isn't it.
Ed knows this bike much better than I, but it seems if the injector is turning on and off as it should then could it be a massive over fueling but it would have to be running with the emissions of a steam engine for fuel to get past the rings. The piston obviously looks like it nipped up and now I'm thinking are you sure there is fuel in the oil. Was it just a seizure. But you're convinced there was and is fuel in there and it must have come from somewhere.
If you've already said I'm sorry but have you posted this on a specific CB125 site?
Is there a return feed from the injector and if so is this clear.
Upt'North.
Still thinking.
23/05/2020 04:54:54 UTC
Upt'North said :-
This is a serious thought, you haven't upset anyone recently who may have extracted revenge.
Upt'North.
23/05/2020 04:58:30 UTC
Jon C said :-
Upt'North Is there a return feed to the injector? Not that I know of. Please anyone correct me if I’m wrong.
Are my sure there is fuel in my oil, the smell is undeniable and I did 10,000 miles changing the oil every 1,000.
However, I can 100% say that before the piston broke last time, I noticed the same issue regarding starting the engine from cold. I had to Also open the throttle to keep the engine running. After warming up, the engine would switch on with no problem. Tomorrow I’ll take off rocker cover, check valve gaps, and look at spark plug gap. I’ve checked the battery and it’s fine.

Thank you for all your advice, you’ve taught me how to check injectors already.
I have posted the question on another cbf125 forum but I’m not getting replies.
23/05/2020 11:51:06 UTC
Ren - The Ed¹ said :-
Upt' and Jon C. From the tank a "low pressure" gravity fed pipe goes to the fuel pump located above the rear sprocket cover. Of course the pump can pump way more fuel than required particularly at low engine loads. As such there is a single high pressure pipe to the injector and a pipe that returns the excess fuel back to the tank. Therefore there is only one fuel pipe to the injector, the return being from the pump.

Now... I'm still curious regarding the various pipes being routed wrongly. If the excess fuel return was located to the airbox or breather not the tank - but that much fuel would be patently obvious I would have thought. Jon C you have a Haynes for the CBF125 if I recall? If you need any pics from my bike just ask.
24/05/2020 11:10:55 UTC
Jon C said :-
Alright. Just about to go out to the back garden and start the work. Cup of tea first. What I’ll do is put a YouTube video up and send you the link so you can have a gander at my workmanship! I’ll try to show the routing of my pipes to and from the fuel tank and fuel pump. I’ll also take the rocker cover off and show you my timing and valve gaps with feeler gauges. Best way to show you the lot. If all looks good, forget it. I’ll just ride and put it through it’s MOT which is due in the next month!!!
24/05/2020 01:07:01 UTC
Upt'North said :-
Check that return pipe is clear Jon.
Upt'North.
24/05/2020 01:39:18 UTC
Jon C said :-
I presume this is the excess fuel pipe.
Looks correctly routed to me?
Posted Image
24/05/2020 02:30:38 UTC
Jon C said :-


Here it is. Hope it’s clear! Let me know any thought maybe please!
Thank you all again!
https://youtu.be/ZEZ4QPZur_8...
24/05/2020 02:57:05 UTC
Upt'North said :-
I'd have the return pipe off to check it's clear and no obvious obstructions at whatever it's connected to.
Upt'North.
24/05/2020 04:41:33 UTC
Jon C said :-
Disconnected and a tonne of fuel poured out.
I presume this is just the effect of gravity from the fuel in the tank?
No obvious instructions.
Posted Image
24/05/2020 05:29:36 UTC
Job C said :-
*obstructions

So I’m guessing this excess fuel pipe is supposed to always be full as you have indicated that it’s job is to return to fuel to the tank. Just caught me out a bit because in the Haynes manual they call this a vapour return hose.
24/05/2020 05:43:10 UTC
Ren - The Ed¹ said :-
Well the tappets look OK. Just checking... you're at TDC between compression and power rather than exhaust and induction.

I'll add a link to a diagram with the various pipes. I'm sort of 98% sure it is NOT bad pipe routing but it can't do any harm to check. Click on "view large image" for a closer look.
https://www.cmsnl.com/honda-cbf125m-2010-a-england_model32261/partslist/F__1300....
24/05/2020 05:49:57 UTC
Upt'North said :-
Yes it looks like it would be full of fuel looking at No. 15. But that confuses me. Not hard.
I suppose there's no reason why it should be clear of fuel as the excess fuel under pressure would push this fuel back to the tank. I think.
Aren't these 125's complicated.
Upt'North.
24/05/2020 06:06:30 UTC
Jon C said :-
Thanks for pipe diagram Ren. Everything looks spot on.
I have just pushed them all in all the way and secured clips where required.
My last question I guess is the one hose that I have not checked. Crank case breather hose. Any chance that could cause these problems?

Timing looks good and tappetts too.

Upt’North is makes sense that this return hose is full of fuel. Thank God I caught it before getting completely soaked.

24/05/2020 06:29:19 UTC
Ren - The Ed¹ said :-
Item number 13. Goes from the crankcase behind the barrel under the throttle body to the lower part of the airbox. I once had gotten water, presumably condensation, in the bottom of the airbox that leaked into the crankcases via this pipe. If there were any way the airbox got fuel in it this would allow fuel into the crankcase. Correspondingly if this were connected to anything fuel wise.

It's a short pipe so easy to follow.
https://www.lingshondaparts.com/partscatalog/catalog/listing/catalog/hondamc/cat...
24/05/2020 07:05:14 UTC
Ren - The Ed¹ said :-
Have you checked the 2 breathers on the tank items 8 and 23 on the first link, the tank diagram? If memory serves these should both come out under the rear footrest to "air". One is from the top of the tank, the filler cap. This catches rainwater and any overspilled fuel. You'll note a hole next to the cap when it's open. The other I think is the tank breather - allowing air in as the fuel drains and pressure out on hot days.
24/05/2020 07:10:50 UTC
Jon C said :-
Ren. I’ve put all the hoses back together, Rocker cover, And spark plug. Refuelled and did a cold start . Started first time. Have no effing clue what is going on. I saw the 2 hoses from the right hand side of the tank And followed them . They are just open to the air at the end. Tomorrow I’ll look at the crank case breather hose so see if it’s got any liquid in it. It is going to the bottom of the air box.

I was wondering what it was doing but yeah. If any fuel has made it backwards from the throttle body it could theoretically make it into the bottom of the engine that way??? Still remains that injector is perfect and not leaking though.
Meh.

Ren, you asked about TDC. The way to know if it’s at compression and power Stroke is that the piston is at its highest position ? Is this correct?
24/05/2020 08:48:13 UTC
Ren - The Ed¹ said :-
Induction, compression, power, exhaust - suck, squash, bang, blow. The 4 stroke cycle.

Induction, piston goes down to Bottom Dead Centre BDC
Compression, piston goes up to Top Dead Centre TDC
Power, piston goes down to BDC
Exhaust, piston goes up to TDC

There are 2 TDCs in the 4 stroke cycle. Tappets are set when the engine is at TDC after compression before exhaust and not after exhaust before induction.

Yay! GREAT! How the chuffing heck do you know WHICH TDC are you at? As you turn the motor (the motor turns in the same direction as the wheels on the CBF125) you need to look at the exhaust valve. If the exhaust valve has just closed when you get to TDC then the piston has come up on the exhaust stroke. If you keep on turning the motor the inlet valve will open. This is the *wrong* TDC between exhaust and power.

Keep on turning, as the piston rises again you might feel the compression of the compression stroke, get to TDC, this is the correct TDC between compression and power.

OR... at TDC look at the lobes on the camshaft. Both the lobes should be down into the head rather than up towards the tank.
25/05/2020 07:53:22 UTC
Ren - The Ed¹ said :-
To be honest if you'd set the tappets at the wrong TDC I think the tappets would be way out so I think you've done it correctly.
25/05/2020 07:57:06 UTC
Ren - The Ed¹ said :-
I've scanned a few YouTube vids and these chaps suggest rattling the valves, if they rattle your at the right TDC, if not then you're at the wrong TDC. Erm. Yes 99% of the time but it would be possible to set the valves totally wrong at the wrong TDC.
25/05/2020 08:00:33 UTC
Ian Soady said :-
If you set them at the wrong TDC (where the valves are usually "rocking" ie one is just closing the other is about to open) then when you get to the right one they will be *really* slack.......
25/05/2020 09:45:35 UTC
Jon C said :-
I can check again, thanks for the explanation. I’m confident that I’ve done it correctly . But out of paranoia I’ll check them out. Not being funny, if I had set them on the wrong stroke would the engine run? The cam shaft sprocket indicator line is horizontal on two occasions, during one, the tappets do not move at all, they are right, during the second, they have a tiny amount of wiggle room. It’s literally something I watched on YouTube. I noticed that on my bike, as on many other cbf125s the indicator circle on the sprocket is under the line and not on top. When I put this engine back together again, I was tempted to put the sprocket in the same position to match the Haynes manual. But I didn’t really mind as it’s an oddity that as long as I know, I won’t make the mistake. First time I checked my bike 2 years ago, both the intake and exhaust gaps were at 0.12 and I also found a spark plug that did not match any suggested by Haynes manual. Speedo cable was broken and rocker holder was damaged. I got the rocker holder replaced by a mechanic because at the time I thought that those jobs were impossible for me. After being hit for £230 I started to formulate different ideas.
25/05/2020 11:42:06 UTC
Ian C said :-
Hi Ren,
Great articles by the wy.
I'm having problems with the bike on tickover just as you discussed earlier in the thread.
What can I use to clean the IACV before I but a new one?
TYIA
Ian C
25/05/2020 02:33:34 UTC
Ren - The Ed¹ said :-
Jon C - I'm now 99.99% sure you got it right I really am. But for those reading this the point remains it is possible to get the wrong TDC. As Ian states if you set it using the wrong TDC the valves would be WAY slack.

Ian - Hmmmm, not 100% sure. I don't think you could clean the inside of the IACV itself as it'll be a sealed unit but you could blow out the passageway the IACV goes into? If there's anything in there making it stick it would hopefully blow out. Either an air line or a tin of compressed air, you can get that from computer shops, they use them to blow the dust out of PCs. I'm loath to recommend solvents simply because I don't know enough to state that they wouldn't damage the plastic of the injector or the IACV.
25/05/2020 04:21:17 UTC
Ian C said :-
Ok Ren. Thank you. Think I'll just buy a new one for the sake of £30.
25/05/2020 05:28:02 UTC
Jon C said :-
Ren et al.
I disconnected the Crank case breather Hose and it’s wet. The liquid does smell of fuel. Would you take out the air box and investigate? Or is this normal ?

https://youtu.be/Kco3hLaTRWA...
25/05/2020 07:59:00 UTC
Jon C said :-
Another update. Took the air filter out and it reeks of fuel.


Posted Image
25/05/2020 08:10:02 UTC
Bogger said :-
Is this not just a residual fuel smell from the 'crankcase breather' system?
From when the fuel was in the engine.

Bogger
25/05/2020 08:53:04 UTC
Jon C said :-
Bogger, yeah. Chicken egg situation. Maybe I should ask the question this way. Is it normal for the crank case breather hose to carry liquid and for that liquid to smell of fuel? Is it possible that during my last breakdown , the vapours got so concentrated In the crank case breather hose that there was a build up and this is the fuel smell I am getting in my oil now? So I suppose it’s worth taking out the air box and cleaning it out?
25/05/2020 09:11:40 UTC
Ren - The Ed¹ said :-
Ian C - I'd still check to see if there's anything in the tube that the IACV goes into. Also be sure to check your tappets! This can have an adverse effect on the idle.

Jon C - there's no point removing the airbox and it'll be the devil's own task. I'd leave the filter out and the airbox open to allow it to breathe. I suspect the smell is residual.

FYI when an engine is running it is inevitable that some, even if it is just a tiny amount, but some of the combustion pressure gets past the piston rings into the crankcase. With the engine creating say 4,000 combustion processes per minute this pressure would build up in the crankcase. The breather allows this excess pressure out. With the oil being hot as well as the nasty fumes from the combustion these oil vapours and combustion gasses are sucked into the airbox and go through the piston to reduce emissions.

The wetness is likely caused by condensation and oil mist.
26/05/2020 08:00:32 UTC
Jon C said :-
Ok Ren . Thank you. I’ll take filter out and let residual fumes evaporate as best I can.
I’m booking the bike in for it’s MOT. And I’ve got to renew my cbt within the next 2 months. Seems like a case of watch this space .
Bike has fresh oil, 10W-40, and I am going to start taking progressively longer rides.
Thank you for all your advice everyone, it’s much appreciated. Fingers crossed this was a residual smell and not a resurfacing of the problem. Time will tell I suppose.
26/05/2020 10:36:07 UTC
Upt'North. said :-
What was wrong with carburettors and external breathers.
Well, obviously the environment and upsetting the odd tree hugger. And climate change supposedly.
But what else?
Upt'North.
26/05/2020 01:07:30 UTC
Ren - The Ed¹ said :-
Carburettors? External breathers??!! Good grief man, are you trying to get us all killed?

Jon C under the air filter is the shiny metal gauze, have you looked underneath that? It ought to be nothing more than an empty plastic chamber with the inlet tract and a few odd shapes, that's all.
26/05/2020 04:08:38 UTC
Jon C said :-
Ren. My God getting to see into the air box is a pain. Yeah. Completely empty. Just a tiny bit of some wetness on the floor of the box but not a hugely strong smell of fuel in there. And nothing else.
26/05/2020 07:58:41 UTC
Ren - The Ed¹ said :-
Yeah the wetness will, or at least should be, oil vapours that have settled. Basically oil.
27/05/2020 07:52:50 UTC
nab301 said :-
That's a curious one, what does the spark plug colour look like or rather what did it look like after the loss of power? What about contaminated petrol? if you've only done 11 miles since rebuild are you still on the same tankful of petrol. Not related but did you check the oil filter screen after the seizure ? I'd be afraid of metal swarf in the engine.
If the injector isn't leaking which you checked I'd check the resistance of the engine oil temp sensor and the IAT (intake air temp sensor) sensor on the air box. It's feasible the bike could be running at max richness because of a problem with either sensor, simulating cold engine /low air temperature ( similar to running on full choke with a carbureted engine).
Nigel
27/05/2020 08:09:42 UTC
Jon C said :-
Nab301. Thanks for your assistance.
I cleaned the centrifugal oil filter and the oil filter mesh. No large pieces of metal. What I did find was a pasty grey deposit at the bottom of my oil reservoir. The spark plug looks relatively clean right now. When I first bought the bike, it had a spark plug in it not recommended by Honda. And when I took it out, it had some serious white deposits in it. I can post pictures if you want to see?
Fuel wise, yes. I was on a new tank , I had refuelled that morning. I remember this clearly. When I did the piston replacement, I drained the fuel and now it has about 3L in there. Also whilst I had the top end off I poured engine oil into the crank case several times to see if I could flush out any chunks of metal. Nothing. I suspect that my piston was on its way out. One of the reasons I say this is that during my last MOT in 2019, the mechanic mentioned that there was an abnormal sound from the engine but he could not put in finger on what it was. His words were, ‘it’s likely that at some point your engine is going to go. But it’s cheaper to buy a second hand engine than for me to investigate’. 6,000 miles later it let go. Now that I have done a piston/barrel change, I can say that the motorbike is vibrating less than I’d becomes used to.
I can check the sensors you have indicated for sure. What readings are my looking for? Maybe this is in a section of my Haynes manual that I have not yet checked.

28/05/2020 05:21:20 UTC
Ren - The Ed¹ said :-
The readings, if there are any, will be in the Haynes.

"abnormal sound from the engine" and "it’s likely that at some point your engine is going to go". My CBF125 has been making abnormal noises since 6,000 miles when I got it. It still makes them now, admittedly they're a bit louder.
28/05/2020 08:10:04 UTC
Bob said :-
Have you checked the fuel pressure to the injector?
Cheap fuel pressure guage sets are on the Evilbay for under £25.
My car had me going round in circles with a running fault until I checked the fuel pressure - apparently fuel pumps can fail by going over pressure.
Try running the engine with a DVM connected across the O2 sensor, it will tell you if it's running very rich.
28/05/2020 09:41:46 UTC
Jon C said :-
Ren, I think Every cbf125 makes abnormal noises. I’m just recollecting what my mechanic told me when he did my MOT last time. Also once it broke down I had the bike towed to his shop, he turned oN the ignition and said , yup engine gone. I was looking back at the pictures I had taken after opening the top of the engine. From my pictures it’s crystal clear that the top ring on the piston had snapped as it had the expected gap on 1 side and a second smaller gap at the side where all the scoring was visible. If you compare the picture I attach now to the piston picture I posted earlier, you’ll see that the top ring actually has 2 gaps. From my understanding the top ring is responsible for much of the compression. Explaining why exhaust gases would have been able to travel through the piston and why I felt a sudden loss of power. The top ring does explain the sudden loss of power. The question remains, why could I smell fuel in my oil at the oil change prior to the breakdown. Was this a gradual failure in the piston ring (does it happen that way) or something else that I have not managed to stop. All of my tests and suggestions provided, indicate that the bike should be working fine now. And that the fuel smell I have is probably residual, possibly from crank case breather hose and air filter stinking of fuel since the breakdown. Does your air filter also smell of fuel? Just out of interest. Maybe it’s normal?
Posted Image
28/05/2020 09:55:17 UTC
Jon C said :-
Bob thanks for your suggestion. I’ve got a DVM but not a Fuel pressure gauge. I’ll look into this.
28/05/2020 10:30:42 UTC
nab301 said :-
Sensor resistances from the Haynes manual . Oil temp sensor 2.4 to 2.9 k ohms @20 deg c
IAT sensor resistance 1 to 4 k ohms @20 deg c
Also from the fault codes page (code 7) Engine oil temp sensor (engine hard to start from cold) default value when fault detected is 75deg c.
IAT sensor code 9 . Engine will run Temperature signal is fixed @ 35deg c
I find the IAT sensor default interesting because in my part of the world the air temp rarely / never reaches 35 deg c and I found in very cold weather the petrol consumption ( on my CB125F) increased a lot, suggesting to me anyway that The FI system was richening the mixture excessively in vary cold weather?
Disconnecting the sensor obviously triggers the engine management light but i have yet to pluck up the courage to run the bike for an extended period without the sensor connected and in any case the FI system may compensate in other areas.. However, I have been using the bike for commuting to work purposes recently albeit a tankful of petrol lasted 2 months, but petrol consumption has measurably improved and the main difference from the winter commute has been higher air temperatures. Maybe I'll have more mileage covered by the end of the year and more data...
On fuel pressure ..... on specific model bike forums over the years "tuning suggestions" ( after fitting free flowing exhausts / removing cat converters) were often to fit the fuel pressure regulator off another model in the range which ran at a higher pressure , therefore acting as a very blunt enrichment device through out the whole rev range. The higher pressure meant more fuel delivered per each opening of the injector.
@ BOB will the DVM switch quickly enough across the Lambda sensor ? I thought you'd need an Oscilloscope?


https://secure.lambdapower.co.uk/diagnosis/diagnostic_index.asp...
31/05/2020 11:14:41 UTC
Bob said :-
The Lambda sensor O/P oscillates fairly slowly, it should typically be 1/2Hz or less. You'll get enough of a reading from a DVM to see what's going on. I did think about using an old moving coil analogue meter but it wouldn't work because of the lower input impedance.
I did this trick on my KLX250, I was playing around with various tuning options from the forums. You know how it is - various genius people suggest super tuning mode. I thought I'd try them out but apply some actual science!
I have seen the increased fuel pressure touted as a tuning aid too. The thing is, these people are messing but they have no understanding of what's going on.
On the failed piston ring YES ABSOLUTELY that ring would explain the smell of petrol coming from your oil. It probably failed when you first noticed the smell but it took all the intervening time to get bad enough to actually kill the bike. I had a Honda 400/4 that did something similar 25 years ago, it was still running despite the rings on two pistons being in pieces.
01/06/2020 07:56:15 UTC
Ren - The Ed¹ said :-
That - that Bob is a very insightful possibility. The rings were partially failed allowing unburned fuel into the crankcase. When the rings fully fail the fuel smell is still lingering. Hmmmmmmm, a wise suggestion.

I can't say I've ever noticed a petrol smell from any filters before Jon C, I'd be concerned if I did.
01/06/2020 10:04:36 UTC
Ian Soady said :-
Re looking at Lambda output - I have an Android oscilloscope app on my tablet. It only needs a cable making up to plug into the microphone socket and you become my uncle.....

This is the ignition trigger output from a Honda 4 I was struggling with a couple of years ago (the fault turned out to be an intermittent open circuit on a plug cap).

As I'm even more of a cheapskate than Ren I thought a free bit of software and a cable I could knock up from odd bits lying about well worth the effort.
Posted Image
01/06/2020 10:19:33 UTC
Jon C said :-
Hello everyone,
Bob thank you for giving that explanation. Hence it makes sense that fuel got into my crank case. I went for a 10 mile ride today. When I came back , I took out the dip stick. There was a faint smell of fuel that dissipated within seconds. I put the dip stick back in and the fuel odour was gone. I think that the fuel smell now is remnant from the previous breakdown. I think from now on, I’ve got to take rides and continues checking. Frequent oil changes will probably do good too.
Fingers crossed. Thank you one and all!
01/06/2020 09:59:47 UTC
Ren - The Ed¹ said :-
Keep us in the loop Jon C, it's been an interesting and educational quandary.

Ian - can you provide more details? Either here or even better a simple post? Bear in mind at least one person (me) doesn't really understand electronics and silly scopes.
02/06/2020 08:27:43 UTC
Jon C said :-
Ren, I will do sir.
Thanks again.

02/06/2020 11:04:30 UTC
Ian Soady said :-
Hi Ren. I just followed the instructions in the link. I'm no electronics wizard either although I do know one end of a soldering iron from the other (hint: don't get hold of the hot end).

Like most people I have various earphone / microphones lying about and I merely cannibalised one of those for the hookup lead. It's a bit fragile but did the job. I don't think the values of the resistors mentioned in the link are critical. The app I used is just called oscilloscope although there are loads around.

With respect to the trace, what you're seeing is the pulses from the ignition trigger. As it's a 4 cylinder with idle spark, you get a negative spike followed by a positive one - at least that's my interpretation.
https://retronics.wordpress.com/2012/07/14/the-0-android-oscilloscope/...
02/06/2020 12:19:23 UTC
Ian Soady said :-
Actually, this may have been the link I used.


http://www.ledametrix.com/oscope/index.html...
02/06/2020 12:23:45 UTC
Ren - The Ed¹ said :-
If I can make sense of these links by re-reading them time and time again it could be an interesting experiment Ian. I can certainly see the advantage of having a scope when it comes to diagnosing electronics. I can use a soldering iron, I have the scars to prove it. It's things like "resistors" and "capacitors" that scare me, fear of the unknown.
03/06/2020 09:02:11 UTC
Ian Soady said :-
There are only 2 resistors involved and the values aren't critical as long as they're in the right ratio. They perform 2 functions: one is to prevent high (well 12 volt or so) voltages hitting the soundcard which is only rated for a few millivolts; the other is to form a voltage divider to give a decent range.

I have to confess that I made it and then hardly used it afterwards. I did try it on the ignition generator on the Guzzi but couldn't work out what I was eeing....
03/06/2020 04:55:06 UTC
Bob said :-
Interesting use of an Android tablet.
I would recommend getting a proper scope though, they're not expensive these days.
I use on of these: https://www.velleman.eu/products/view/?id=384090&country=us&lang=en
It's only single channel but it's actually quite a decent thing.
The thing to look for with oscilloscopes is the sample rate.
There are cheap android based scopes on Ebay and Amazon but the sample rate is often only 200KHz or lower.
Basically if you are trying to get a good view of the shape of a wave you need to look at it very frequently, the rate of "looking at" is the sample rate.
On the example Ian posted, if his sample rate had been too low you might not have been able to see those postive and negative spikes.
So the higher the better, that Velleman scope is 40MHz which is actually not bad and despite what you might think nothing in vehicle electronics happens very quickly. 10000 RPM is only 100 micro seconds per revolution. In my field of industrial electronics we're routinely working the GHz or 1 nano second region (100000 times faster).
The advantages of a "proper" oscilloscope are manyfold and unlike the software Android versions offer selectable input ranges (no resistors needed), high imput impedance (just trust me this is important), higher sample rates, multiple trigger modes etc. etc.
I picked up the Velleman for £65 on the Evilbay, I can thoroughly recommend adding one to your toolbox.
04/06/2020 09:58:52 UTC
Ian Soady said :-
£65 is still quite a lot (and £65 more than I paid) for something I would only use very occasionally. In fact since our house move I can't even remember where I put the lead I made up.....

The main disadvantage of the android bodge apart from what you mention is that (apparently) the sound card will effectively remove any DC offset but it's fine for AC. But my knowledge of oscilloscopes is minimal.
04/06/2020 11:22:56 UTC
Bob said :-
Ahaa! Yes, I forgot that - Oscillosopes have switchable AC or DC coupling, which can be invaluable. For example looking at the slowy changing output from a Lambda sensor on an AC coupled scope may well show nothing at all and if it did you certainly wouldn't be able to tell if it was moving between the magic 0.1V and 0.9V
And also I can measure up to 300V with that little Velleman - I'm not sure I'd want to stick 300V up my Android phone!
04/06/2020 11:47:54 UTC
Ian Soady said :-
Hopefully the resistor network will be enough to cater for the kinds of voltages we find on our bikes - if I saw 300 volts I'd be a bit worried....

Would a standard digital voltmeter cope with the lambda voltages? I also have a somewhat antique analogue multimeter which is useful for checking capacitors. But more recently I got one of these (see link)
https://www.ebay.co.uk/itm/All-in1-LCR-Component-Tester-Transistor-Diode-Capacit...
04/06/2020 12:11:46 UTC
Bob said :-
Yes a standard DVM will work on lambda sensors. I did this with my KLX - went for a ride with a DVM strapped to the tank when I was testing the effect of tuning mods.
The key to it is that lambda sensors have a very high output impedance, which means whilst they generate the signal voltage there isn't much shove behind it so if you connect it to an instrument with a low input impedance it will pull down the voltage of the signal.
For this reason moving coil meters (analogue) are unlikely to work because the meter needs the signal that is being measured to cause current flow in the coil to make the needle move.
DVMs, even cheap ones will typically have an input impedance greater than 200K Ohms and the better ones are over 1M Ohm.
The higher the input impedance of the meter the less effect the connection of the meter will have on the signal you are trying to measure. You can never eliminate it though.

That component tester looks interesting, cheap enough too!
Be mindful that it will be probably be taking it's readings at one particular frequency, so depending on what component type you test the results might vary from the component's stated value.
04/06/2020 12:59:01 UTC
Ian Soady said :-
I've remembered why I actually bought it and it was to try out as a timing tool for magnetos (as you will know, the difference in resistance between points closed and open on a rotating coil mag is very small). But it wasn't any use for that as it had a long dwell period once things were attached. It is however useful for checking out odd components - as I say, capacitors but also diodes etc.

I always go for the cheap option - preferably something I can knock up from the scrap boxes for nowt!
04/06/2020 02:48:53 UTC
Upt'North said :-
Ian, it's just struck me, I'm not as quick as I used to be. Wasn't that quick then.
Whilst I enjoy a little tinkering and even some monotonous maintenance the thought of checking electrical items in the manner described is above my pay grade, or I can't be arsed, probably the latter.
Then I thought, light bulb moment, I realise it's because I am fortunate enough to have good folk at hand who charge little for such work and know much more than I.
This of course will change going forward, Little Ritchie will retire and Big Michael will realise he can make more money just changing out bits than bothering with the likes of me.
Damn and blast, best get some reading in and swot up.
Upt'North.

04/06/2020 03:03:08 UTC
Ian Soady said :-
I suppose this all stems from having very little cash to pay anybody else to do anything for many years. So needs must.

Added to which it is rarely the case that anyone else takes the same care of your vehicles as you do. A case in point. I used to take my Discovery to a chap who was Land Rover trained, had worked on them for decades and was highly regarded. One day I asked him to do a job that required removing the viscous fan Now I had changed this fan myself a few months earlier and had made a point of buying the correct enormous spanner and locking device to avoid damaging the securing nut. When I picked my Disco up from him I noticed that a cold chisel had been used to remove said nut - witnessed by the gouges.

Now of course that did the job but left nasty marks on the nut. If I'm paying (as I was) £80 an hour I expect the right tools to be used.

I'm now in the fortunate position to pay people to do things I don't want to do like building work, decorating etc. But let some "expert" touch my Norton or Guzzi? No way.
04/06/2020 04:50:39 UTC
craigyboy said :-
I have a question will a k&n rc-1060 air filter damage my engine or fuel injection system
09/06/2020 09:50:07 UTC
Bogger said :-
No. But it may affect the performance and not in a good way. Try it and see what the outcome is.

Bogger
09/06/2020 10:14:54 UTC
Ren - The Ed¹ said :-
craigyboy - I could not say for sure whether or not the K&N air filter would harm the engine. If you want my opinion I'd say probably not BUT for the sake of maybe a tiny increase in power why would you risk damaging your motorcycle?

Airboxes aren't just randomly thrown in the bike to make them slower or achieve emission controls. There's all kinds of pressure waves, pulses, echos and flow considerations going on that are far far beyond my understanding. I realised this when looking at my own CBF125. From the airbox to the throttle boy is a rubber pipe. On that rubber pipe is a curious plastic item, a simple chamber, a dead end box about the size of a Kazoo. It's called a resonator. It's purpose? Something to do with controlling pressure waves, dampening them and controlling them. The point is it ain't simple.

If it's an old knackered field bike then fit the filter, see if it makes any difference. If it's your daily driver that gets you to work and back, keep it standard.
Posted Image
10/06/2020 08:15:35 UTC
Upt'North said :-
A new clean OEM filter will be all you need. The K and N will give you about 0% of sod all extra performance.
Upt'North.
10/06/2020 09:30:46 UTC
Jon C said :-
Update. I’ve been taking short daily rides. Today I pushed it to doing a few miles at 50 mph. I have a rocker cover gasket Oil leak. That’s easy to resolve. I have a spare gasket and gasket sealant so I’ll do that. 2 things however concern me. 1. The bike has that distinct smell of overheating.
2. The only other issue is that after I take a ride and let the engine cool for an hour. When I take out the oil dip stick, I can still smell fuel.
There isn’t anything that any of you can think of that would link these two issue as a problem you’ve seen before?

14/06/2020 07:32:52 UTC
Ren - The Ed¹ said :-
The smell of overheating *might* be the stuff just burning off the engine after all the work? I mean mine whiffs somewhat after it's had my greasy paws all over it. That said after 50 miles that should have all burned off. The only way to know for sure is to get one of them digital thermometer thingies and get an actual number.

As for fuel in the oil. Sheeez mate, I haven't got a clue after all the checking and double checking you've done. The only thing I'm coming up with is to get the oil tested and see if there is fuel in there.

'Snot the wife is it? Maybe she doesn't like you riding, maybe she's trying to drive you insane.
15/06/2020 09:00:37 UTC
Jon C said :-
Hello Ren,
It’s starting to feel like someone is trying to sabotage me! I agree with you, with all the work I’ve been doing on the bike, it is possible that it’s the oil and fuel residue burning off.
I do know a certain someone who does testing of engine oil. Or at least, says he does, will see what he says.
I don’t know if I’ve asked this before, after going for a ride and letting the engine cool, when you take the dip stick out, can you smell fuel? Tried this on my car and the answer was no. But obviously completely different vehicle.
15/06/2020 10:54:08 UTC
Ren - The Ed¹ said :-
I shall endeavour to check after my next ride Jon C.

I did notice the other day after parking the 500 it was HOT! I had to stop and have a think. I suspect it is merely the weather in this instance. The 500 is water cooled so scientifically, numerically it would only have been the same temperature as usual, maybe a couple of degrees warmer at most. Yet with the warm air *and* the heat radiating from the motor it *felt* hotter than I'd expect.
15/06/2020 05:02:37 UTC
Borsuk said :-
I think the design for motorbike air systems is complicated not so much because of the science behind it but because the engineering comes last in the design process.
Let me explain.

Marketing director goes to head of Motorbike company and says “ Large capacity adventure bikes are the in thing.” Big boss says, okay we will make one.
Marketing manager then says to “Stylist” we want a 1200 cc adventure bike with the following power, torque and bling specs and a 400 mile tank range, and most important make it lightish and sexy and cheaper than the oppositions.
“Stylist” then designs a work of art with appropriate sexiness, bling and size and hands this design to the engineers and says, “Here is my labour of love” All you have to do is fit 1200 cc engine, suspension, cooling system and drive train in the 1201 cc space I have left you that is not covered in plastic.

Engineer then goes away swearing and cursing as he tries to shoe horn all this into the limited space available hence the convoluted breathing systems.
But we cannot pity the engineer too much as he has already sold his soul to the devil as the words maintenance access does not even cross his mind during this.
Who cares if the bike has to be taken apart completely to change an oil filter, keeps the dealers in business with labour charges.

Ships are designed in a similar manner but everyone apart from the engineer is replaced by the word accountant.

16/06/2020 08:16:58 UTC
Ren - The Ed¹ said :-
You're very cynical Borsuk, but to a great extent quite correct. Honda, Kawasaki and the rest of the marques are NOT in the business of selling well engineered items suitable for a lifetime of DIY home mechanicing. They sell new bikes to new bike buyers. And new owners (mostly) are not interested in getting the tools out. New bike buyers want "...est", fastest, sleekest, sexiest, most powerful, you get the idea.

We the plebs, we either but used bikes which doesn't actually help Honda et al, or if we buy new we will attempt to service them ourselves, which doesn't help the dealers.

Imagine a world where a marque makes a motorcycle designed to be easily serviced, easily diagnosed (ECU computers with USB connections and readily available software) and easily take-apartable. The bike wouldn't be as sleek or stylish as the competition so it wouldn't sell as well. Dealers wouldn't like to sell them as there's nothing in it for them.

Shame, real shame, but tinkerers like we are in the minority.
16/06/2020 11:58:16 UTC
Jon C said :-
Something is still wrong with the bike. Took it out for a spin. About 3 miles. Reached 50 mph. When I stopped I could smell hot metal and melting plastic . The smell was not coming from either side of the engine nor the exhaust. It was definitely coming up from the front of the fuel tank. Rising from somewhere underneath. Also the bike took several attempts to re start. I’ll check the engine temperature sensor and wiring tomorrow to see if it’s working. I’m wondering if it’s not working, if it could be causing the engine to overheat? Would a failed temperature sensor not cause an engine warning light to come in?
I’m starting to get fed up with this cbf125 and am seriously tempted to part exchange it for something else! If I can convince my wife, I’d like a little Aprilia RS125
19/06/2020 08:04:52 UTC
nab301 said :-
The oil temp sensor is just used by the ecu in conjunction with the air intake sensor to control fueling , It can't really cause the engine to overheat unless it runs extremely lean I guess because afaik if it goes out of spec the ecu ignores the readings from the sensor ( throws a fault code) defaults the signal and sets the fuelling to suit an assumed oil temperature of 75deg which will be ok once the engine is hot. . (mentioned earlier in this thread. If you remove the connector from the sensor and check the resistance value of the sensor you'll know if it's faulty.
Also , if you loosen the bolt at the right rear of the valve cover and turn over the engine just to ensure you have oil getting to the valve gear . Or failing that , remove the valve cover to check that there is plenty of oil there . With the damage that your engine incurred it's possible that without a full strip down there are blocked oil ways within the engine . It's an air/oil cooled engine if oil isn't circulating properly it'll overheat / seize. Also the piston barrel may require running in if the tolerances are tight and maybe 50mph is a little fast at the moment?
As for the Aprilia RS 125 if it's the 2 stroke one , well , lets say if you think you have problems now....
Nigel
19/06/2020 09:08:54 UTC
Jon C said :-
Thanks Nigel,
I’ll check the resistance level of the oil temp sensor tomorrow. I took the rocker cover off recently as I had a gasket leak. What’s your advice on running in a new piston? How many miles do you reckon at lower speeds?

And no. No way Id ride that 2 stroke mini monster. I meant the newer 4 stroke version. I’m looking at the ktm rc125 as well at the moment.

Cheers,

Jon
19/06/2020 10:12:35 UTC
Ren - The Ed¹ said :-
You are having the worst CBF125 experience ain't ya Jon C! Holy cow this reads like a horror story. I know that feeling, enough is enough and you just want out. I got to that stage with my CBF250 then when I finally cracked the problem I still had lost that feeling.

Hmmmm... used CBF125 with some issues for sale... where do you live Jon? No, no I can't, I don't have anywhere to store another bike. Sad.
20/06/2020 09:18:29 UTC
Jon C said :-
Ren... hahahahaha!
Very good! Do you want me to do a walk around video of the bike !
Nah, listen. It’s been good to me. I just wish I could get a handle on what is wrong. I’m Seriously wondering If it’s me being paranoid. There is a reason I own this bike. Because I knew that I could replace every part cheaply. So I still want this to work out because it’s a hell of a lot better than trying to sort out a finance deal to pay for those other bikes for the rest of my life.
In all seriousness, how many miles should one do at low revs when a new piston and bore is fitted?
20/06/2020 10:36:36 UTC
nab301 said :-
My newer model CB125F handbook suggests 500kms (300miles ) avoiding full throttle starts and rapid acceleration along with riding conservatively.
Nigel
20/06/2020 07:58:24 UTC
Ren - The Ed¹ said :-
Whereabouts do you live Jon C? I'm near Bolton and I'd come and have a look but if you're in Kuala Lumpur that might be a tad too far.
20/06/2020 10:06:50 UTC
Jon C said :-
Ren. If you’re in Bolton. We are not close. Might as well be Kuala Lumpur mate. I’m in south Cambridgeshire !

Nab, I’ll take it easy. Although, I must say that I consider 50 mph taking it easy. Where I live all the roads are 40-50 mph Pretty much. To stick to 30 mph I have to find the back roads. Can’t even get to my local train station without reaching 50 mph.

Put fresh fuel in the bike today and it started like a charm. Meh.
I seriously need to get a full license. Easier said than done at the moment. Test centres are telling me to wait as long as possible before contacting them as they’re hoping rules will be relaxed.
20/06/2020 11:08:47 UTC
Upt'North said :-
Jon, don't know if it's near you or not but we stayed at a fine establishment at Elton on the way back from Italy on the BeaST. I think it was The Crown Inn. Very friendly Northumbrian landlord and all the locals had biking stories to share over a pint or two.
Good parking and food too.
Upt'North.
21/06/2020 09:17:44 UTC
Jon C said :-
Upt’North good to know! I’m only 45 minutes drive from the Crown Inn. Never been , but once we are back to some kind of normality, I’ll ride in my cbf125 up there if it’s still with me by then.

Jon

21/06/2020 02:48:34 UTC
Ren - The Ed¹ said :-
South Cambridgeshire? That's that "south" thing innit? There's rumours about that south place, I hear them a lot around here. Apparently there's a disorganised bunch of plebs in an old building what think they run the country, some old lady with a posh voice and a golden carriage and some people in flash cars who make money out of nothing by buying and selling things they've never seen or touched. If we had any of that kind of nonsense up here they'd confiscate your cloth cap and remove the ferret from down ya pants.

I'm also told they have "sunshine" down south. Is it true, does the rain actually stop there from time to time?
22/06/2020 07:37:08 UTC
Jon C said :-
We have sunshine, a golden palace and a big yellow haired guy who tells the whole country what to do.
We have an old lady married to an old guy who has issues with driving.
We have trains that help us reach the capital in 45 minutes , loaded with people who don’t care to wear any PPE. I need a motorbike licence , it may well be that relaxation announce by the yellow haired fella will allow me to do that soon.
23/06/2020 10:54:40 UTC
Ren - The Ed¹ said :-
It sounds awful Jon C, funny though.

If and when you feel the urge we'd invite you to ride ooop norf. You'll need your thermals, your waterproofs, many layers of clothing and of course a cloth cap. Make sure the cap isn't too clean otherwise people will know you're a "southerner". Mind you the moment you speak we'll know. I'd suggest you find a good translator for each area, particularly Wigan, Northumberland and Scotland (I can help with Wigan). Even once Covid-19 has entirely passed I'd still recommend PPE as most of us a riddled with various contagions and infections.

Another thing to note is we do have "hills" ooop norf. No not this little bumps you call "The Chilterns" or "The South Downs", I mean proper hills where you have to drop a gear or two to get up them.
24/06/2020 08:09:35 UTC
Jon C said :-
Ok update.
Went out for a ride and no issues. I think the smell coming from under the tank is a small amount of oil Escaping from the rocker cover. I’ll keep running the bike at no more than 40 mph and see how it behaves. The oil level is not increasing although the smell of fuel in the dip stick is still there. It dissipates and on second dip it’s gone. So I’m going to guess that this is normal? Still would like to know if other cbf owners find the same.

25/06/2020 08:47:40 UTC
Ren - The Ed¹ said :-
It was very hot yesterday evening. After 2 hours and some overheating issues (more on this soon) I smelled my bike. Yes hot plastic around the headstock. Perhaps a hint of petrol from the dipstick, more like hot oil really as I'd expect.

Keep checking the levels and let it settle in.
25/06/2020 11:18:56 UTC
Max said :-
Hi.. Bought a 2009 cbf 125 and it won't fire up. I've replaced the plug, fuel pump and battery and still nothing. I've checked the injector and it's misting when hitting the button so seems to be okay. I opened up the air box and sprayed a little easy start in and it fired up and and could rev but it died maybe 10 secs later. Any help would be appreciated
01/07/2020 03:01:30 UTC
Ren - The Ed¹ said :-
Check for a spark at the plug tip. Worth noting I've had trouble with the plug cap.

Compression. Check and set the tappets first.
01/07/2020 07:10:53 UTC
Max said :-
Hi thanks for response.. Its sparking okay.. The bike fires up okay with easy start sprayed into air box but quickly dies down once the easy start has passed through so compression must be okay. Am I correct in saying if the tappets arent right or the valves are bent then it wouldn't fire up at all? When I first changed the plug it fired up straight away and stayed running for a few minutes and died. I did notice the bike got pretty hot real quick. I've ordered a new throttle body.
01/07/2020 01:16:10 UTC
Ren - The Ed¹ said :-
Hi Max. If the valves are bent it wouldn't start, but tappets that are a bit incorrect can cause tickover issues. For the sake of an hour's work it really is worth checking the tappets, eliminate that potential problem.

However the easy start and fresh plugs does steer me away from tappets. Air leak? An air leak between the throttle body and engine in particular would cause the bike to run lean which would heat it up rapidly. Check for air being sucked in around the throttle body and don't ignore the airbox side either.

Still, check the tappets as well as a matter of good servicing.
02/07/2020 09:00:13 UTC
Jon C said :-
Hello everyone,
After much deliberation and concern on job retention , I have decided to save my money and keep my cbf125. I might just put a new set of valves to put the bike in the best shape possible after having done a piston replacement. When I took the top end apart, I remember seeing a lot of black carbon deposits in the valves and thinking that I may need to de coke or replace. At the time , I opted to just put new valve seals in place. Quick question, I’ve heard of valve lapping. How difficult is this to do ?

Thank you!
03/07/2020 10:26:38 UTC
Upt'North said :-
Valve lapping isn't difficult or expensive, hand lapping kits are cheap (check out ebay/amazon) and other than sore palms there's little pain. I don't know the specifics of how much work it'll take to get to your valves but you'll need a valve compressor tool as well to get the collets out.
There's nothing to fear in the lapping process and I'm sure youtube will have a few thousand videos to follow. Depending how bad they are it shouldn't take too long to do.
Hope it helps.
Upt'North.
03/07/2020 11:55:20 UTC
Jon C said :-
Thank you Upt'North! Right, I’ve got a valve compressing tool. Used It to change the valve seals. I’ll check out the lapping kits and order. I presume that to do this , all I need is to remove the Fuel tank. I did the piston and barrel change with the whole engine out. But regretted it when it was time to put the engine back into the frame on my todd.

Thanks again,
04/07/2020 01:34:44 UTC
Upt'North said :-
I don't know if you can get the head off without engine removal but someone here will.
Upt'North.
04/07/2020 09:49:37 UTC
Ren - The Ed¹ said :-
Hi Jon C. The head will come off without having to drop the motor. If you've done the valve stem seals then you're already way ahead of the curve. Lapping is easy it just takes a while to do it properly. As Upt' says there'll be countless youtube videos that'll get you going. Personally... I wouldn't bother but if you've got the time and enjoy tinkering then crack on squire.

Get the head on a box or similar in the living room with your favourite film on and just lapp away, slowly but surely. The thing to watch out for is to ensure there is zero, none, nada, zip grinding paste left on the head before you rebuild it. The grinding paste is very, erm, grinding and wouldn't do the engine any good at all if it got into the oil.

I, erm, err, I washed my 250 head in the sink with thinners then washing up liquid and anything else lying around in the kitchen and shed. After a thorough rinsing to ensure nothing flammable remained, to get it totally dry I put it in the oven at gas mark 3 for an hour. This is not recommended mechanically, more importantly it is not recommended if you have a live-in partner.

Just be sure to remove all the grinding paste.


04/07/2020 10:13:06 UTC
Jon C said :-
Thanks Ren. Cool. I will definitely get this done. I have been watching videos Overnight to see how it’s done. Rough and then fine grit . Completely understand your point about removing any traces of grit. One last thing. Lapping is something that has to be done on any new valve right? Even if I was to buy a whole new top end (As shown, by the way, would you buy this? Seems cheap to me. Is it garbage?). I would like to ensure this engine stays solid for another 10,000 miles at least, as I’ve been using use it on dual carriageways for sitting at 60 mph riding from south cambs to central London. Annual train ticket prices are £4.5k and the bike has been a huge money saver (wish I knew where that money saved went though).

As always, thank you for your advice
Posted Image
04/07/2020 11:21:40 UTC
Ren - The Ed¹ said :-
If you look closely at several of the Chinese motorcycles they are direct copies of the CBF125 engine - hence the cheap parts available. I struggle to form an opinion on the quality of these parts. I've seen some godawful Chinese parts and equally I've seen some very high quality stuff. The engine on Sharon's Keeway is a work of art, beautiful castings.

Now there is a thing I've heard of but know nothing about properly. Hopefully someone else can guide (ha!) me here. Don't simply assume all you need to do is lap the valves. I think something has to be done with the valve guides, the tubes in which the valve slides up and down. I don't know the what's why's and wherefore's but before you get carried away, do some research on new valves in old guides. I could be way off I just think it's worth checking.
04/07/2020 11:31:38 UTC
Ian Soady said :-
You never (well hardly ever) use coarse grit. I still have the double ended tin of grinding paste I bought decades ago and have probably used it a dozen times - but the coarse end is virtually untouched. Coarse paste is used for some specialised tasks eg grinding in cylinder head joints with spigots on some older bikes like my Norton but never for valve grinding. If you do use the coarse grade you're likely to pocket the valves (ie over-grind them) which will reduce performance apart from anything else.

With respect to valve guides. I think Ren is confused by the fact that when new guides are fitted sometimes they're not directly aligned with the valve seat so that needs to be cut. You should however check the side play but (a) figures are probably not available for your bike and (b) what would you do if they were "wrong"?

In fact if I was you I'd probably go for that new head if it was of decent quality.

If you decide to grind the valves, one of these: (see link) is a handy gadget and saves wear and tear on the hands. But at half the price of a new head when you may only use it once?
https://www.amazon.co.uk/Gunson-G4095-Eezilap-Valve-Lapper/dp/B0012MCW06...
Posted Image
04/07/2020 12:22:24 UTC
Ian Soady said :-
ps the other thing is that the valve seats may be very thin and not have enough meat for enthusiastic grinding....
04/07/2020 12:23:14 UTC
Upt'North said :-
Ed, I feel deflated, I've only got a stick with a rubber bung. Although I suspect the rubber would disappear to dust if I used it, it must be thirty years old at least.
Jon, be careful buying cheap sh.....parts, I'd fix what you've got first. And yes Ian is right go easy, keep checking the lap on the valves, when it's nice and even it's done. A rubber and stick is cheap and not overly difficult to use. If your palms are delicate wear gloves.
Pete, I thought it was just me here scratching my head.
Upt'North.
04/07/2020 01:34:36 UTC
Ren - The Ed¹ said :-
Yeah I have a stick with a rubber sucker on each end (big, small) and rough manly hands (I'm a programmer by trade, hard graft see). Thank you for putting me on the right track re valve guides Ian, I still have much to learn.
04/07/2020 01:54:49 UTC
Ian Soady said :-
Valves are properly ground in when the surface of both valve and seat are an even matt grey. To check, assemble the valves with springs, put the head upside down and fill the combustion chamber with paraffin (if you can find any). There should be no leakage into the inlet or exhaust ports after a couple of hours.
04/07/2020 02:43:56 UTC
nab301 said :-
@ Max , strange , if it runs on easy start and the injector appears to be spraying ok is the fuel in the tank fresh ? Normally if an engine starts on easy start even if the fuel is ancient it'll keep running but if you haven't already done so I'd drain the tank completely and add fresh petrol .
Nigel
04/07/2020 08:31:47 UTC
nab301 said :-
@ Jon C , the specs for all the cylinder head components are in the Haynes Manual , valve stem diameter, Valve guide bore diameter, valve seat width ( narrow @ 1mm) but the tools to measure the clearances would probably cost more than a new cylinder head ... although you may need to measure the clearances on a new head. If Google is correct your journey is possibly 50 miles each way ? That's asking a lot of a 125 at 60mph Imho . I have a 2019 CB125F , it might do a genuine 60mph on the way down if I rode it off the edge of the cliffs of Moher here in Ireland , otherwise it needs downhill on a road with a tail wind but while I did touch those speeds briefly as part of the running in process I tend to limit my throttle position to half for longer journeys . There's no engine designed to run absolutely flat out and last any length of time even if it only produces less than 10 bhp @ the back wheel.
Nigel
https://www.cliffsofmoher.ie/about-the-cliffs/the-cliffs-at-a-glance/...
04/07/2020 08:49:24 UTC
Bogger said :-
Just a quick tip reference lapping in the valves on small capacity machines. I've found that the suckers on the valve lapping tools can either too big to contact the valve head properly and or, not flexible/supple enough to get good contact on the flat valve surface. So they also have a habit of dropping off

A cheap and effective way to lap them in is to insert the valve with the grinding paste already in place into the head. Now push a piece of rubber or plastic pipe over the protruding valve stem and whittle away to your hearts content. The pipe never comes off, until you want it to.

Bogger
05/07/2020 07:20:36 UTC
Jon C said :-
Hello everyone,
Thank you for your huge amount of wisdom.
I understand 100% that my journey is brutal for this bike. I did 10,000 miles on this journey up until it let go . Funnily enough, my bike could hold 60 mph as indicated on the Speedo without the throttle being fully opened or red lining. It involved 30 miles at higher speed before reaching the north circular when it came into its own at lower speeds. I bought the bike for just a grand knowing that it needed a bit of work. But working on the bike has so far been so easy that I’ve grown fond of it. I 100% also understand that I have to move to a higher cc bike ASAP. My mechanic did tell me that for my journey, the very smallest engine should be a 500cc. But until then, I simply have to get the engine into the best condition possible. At the very least , so that when selling, I can have peace of mind that I’ve done the best I can to ensure the bike is going to be reliable for the next user. Nab, I have also owned the cb125f. And I can say that it is down on power compared to the older cbf125. It red lines quite a bit sooner. I was quite shocked at that and you may not be surprised to hear that I obliterated the engine on that bike very quickly. Thankfully, someone came along to buy it off me pretty quickly .

I’m going to open the Cbf125 engine up next week and look at the valves and the top of the engine properly.
I want to first clean up (what would you recommend to de coke?) and then do some kind of leak test. I’ve got a few litres of paraffin , so I’ll do the test that Ian suggested to see. If there is any leakage, then new valves and valve lapping will be done. No coarse grit and gently. And using tricks that you’ve all suggested (Such as what bogger indicates).


Thanks again everyone! You’ve become my go to place to avoid silly mistakes!
05/07/2020 09:42:09 UTC
nab301 said :-
I'd check for leakage when you remove the cylinder head but before you dismantle it so you'll get an idea of the condition of the valve seats currently. For decoking the back of valves I'd use something like a brass wire brush of the type that fits into a drill chuck. Also i'm sure it's mentioned in Haynes manuals but when you go to remove the valves you may find the collet groove is burred and will prevent it being pulled out through the valve guide in which case you'll need to deburr it with a small file . Given the sustained high revs I'd check the free length of the valve springs and compare with the specs in the manual and also check that the valve collets and retainers are in good condition, I've no experience on the little Honda but on other high revving engines I've worked on in the past the valve collet retainers can wear allowing a dropped valve with catastrophic ( for the engine !) results.
Checking with online parts suppliers , wemoto , Fowlers etc indicates that they don't carry any of these items ex stock which if you're a glass half full type of person suggests that there's no demand for them .... so maybe that's good news , they do stock tappet adjusting screws and cylinders and pistons though .....
On the CB125F , like you I found it to be very undergeared which in an urban situation allows 5th gear to be used all the time , I did raise the gearing by one tooth on the front sprocket which helps slightly.
Nigel
06/07/2020 01:27:46 UTC
said :-
Hi guys.. Thanks for the help.ive checked the valves and timing and no problems there. So far I've replaced the fuel pump, spark plug, throttle body, battery, and air filter. Didn't replace the injector as it was working as should so just gave it a good clean. After all parts replaced it starts but dies within a second or two. I've also checked compression and that's fine. Will run for a good 5-10 seconds on easy start but dies once it's burned of. Valves are are also in correct position when the piston is at top. I'm out of idea's now.

Maybe needs someone else looking at it.


08/07/2020 03:20:51 UTC
Ren - The Ed¹ said :-
I must admit I'm befuddled now. If it starts on easy start then mechanically it can't be far off right. Sensor issue? Computer fuels rich for startup then reads the say temperature sensor and decides it is warm and reduces fuel? I'm guessing here.
08/07/2020 09:24:45 UTC
Jon C said :-
Said where are you located?
I’m no expert like many of these old boys. But it sounds like a fuel issue.
You’ve got spark, injector is working, but is it delivering the right amount of fuel? Seems like you could do with a few spares from working bikes to try and diagnose.
The crappy weather has prevented me from working on my bike. Back garden is turning into a pool!
09/07/2020 01:34:46 UTC
Jon C said :-
I should correct. I’m no expert , UNLIKE many of these young (!?!) boys.
09/07/2020 08:25:09 UTC
Max said :-
Hi.. I'm from Fife in Scotland. The bike is really pissing me off now lol. Replaced a few parts and the f****r is getting no further forward. I did forget to mention that I noticed it's had a 150 kit put on it and dunno if that's maybe part of the problem.

Thanks again everyone for the replies
09/07/2020 08:53:38 UTC
Jon C said :-
Max, I’ll have to defer to others’ greater knowledge. But this is an important detail. if you’ve ruled out everything else then I think the big bore is the issue. I thought that on a cbf to achieve the conversion properly, you need to also make sure you have a larger connecting rod? I wonder if You’d have to take the engine apart and check that this might be part of the problem.
I also don’t know if you need to adjust air/fuel mixture for a larger bore?
Anyone done a big bore conversion on their cbf 125s?



10/07/2020 11:26:12 UTC
Bogger said :-
A big bore kit is just that. A larger diameter barrel and piston.Not a longer stroke. So the conrod/crankshaft does not come into play.

Usually what you get with a big bore kit and a standard carb and or fuel injection set up, is more torque and hardly, if any greater power. So better uphill/headwinds but not any faster.

So basically with a big bore kit, regardless of how the fuel gets into the combustion chamber, it will run and usually, for the most part run ok.

I don't know the complexities of the cbf125 fuel system, but I'm led to believe that a fuel injection system will, to a degree, re-learn itself to the parameters of the increase in displacement to make the engine run properly.

If it runs on easy start it sounds like a fueling issue to me. But ultimately could be anything.A compression test would be a useful thing to do. If it reads over 100 psi. It should run.

Bogger
10/07/2020 12:01:21 UTC
Ren - The Ed¹ said :-
Agree re compression test. If the bore kit is "off" or something else is off then maybe the super explosive easy start gets it going but it can't sustain itself?
10/07/2020 12:48:06 UTC
Jon C said :-
Ok. Good weather today, so I’ve take the top of the engine off.
Valve leak test with paraffin sitting outside. In the mean time I’d thought that I’d show this. My motorbike has only done 60 miles after the piston was installed.
Took the rocker cover and all looked good. Plenty of oil...
Posted Image
12/07/2020 01:04:34 UTC
Jon C said :-
This is what the valves look like. The larger valve (exhaust I think) is covered in carbon deposits . Is this normal?

Posted Image
12/07/2020 01:07:00 UTC
Jon C said :-
Top of the piston doesn’t look great. I wouldn’t expect this at 60 miles Post installation . But if valves are caked in carbon deposits then maybe I shouldn’t be surprised?
Whilst I wait for valve leak test, I am going to take the Barrel out to have a look if there is any Scoring/damage to the wall. This will also give me the chance to look and make sure the piston ring installation was good.

Any thought on any of the images? Anything raising red flags?

Posted Image
12/07/2020 01:12:12 UTC
Ian Soady said :-
That cylinder head face looks as though someone's been driving wedges in to separate it. It's a mess and may be one reason you're losing compression.
12/07/2020 01:52:15 UTC
Jon C said :-
Hello Ian,
This lifted clean off without any need to wedge anything into it? Do you mean the Metal gasket looks awful? I only put it in 60 miles ago...

One thing that I have just noticed is that the piston retaining clips were put in where the orientation of their opening is the same as the gap in the piston. I’m going to have to rotate them to the opposite side.
Posted Image
12/07/2020 02:04:10 UTC
Ian Soady said :-
No, it's the face of the head that looks all scratched. Have you had the bike from new or maybe someone has been in there before you.
12/07/2020 03:58:05 UTC
Jon C said :-
I installed a new barrel and piston just about 5 weeks ago. The rest of the engine including the head is from the previous owner. Do you reckon I should buy a new one and replace this one? With new valves etc?
12/07/2020 04:37:31 UTC
nab301 said :-
The larger valve is the inlet , the exhaust valve is cleaner because it runs hotter than the inlet . Even so the inlet valve does look like it has a lot of carbon on it , not sure if you cleaned it before you reassembled the last time. It's hard to tell whether there's a good seal between gasket and head and also hard to tell looking at the gasket.
There should be a clean sealing surface ring on the cylinder head and the gasket surface should have a similar sealing ring with no blow by.
I'd check the cylinder head with a straight edge ( steel rule ) and a thin feeler gauge for any signs of uneveness or indentations on all the diagonals and in between and while you're at it , maybe check the cylinder(barrel) sealing surface is straight too
I'd check also that there's no carbon build up on the back of the valves (on the inlet and exhaust port side . Also have you a photo of the spark plug? Also it could just be the photo but there's a mark ( it may just be oil) running vertically down the rear piston skirt.
The head gasket will need replacing too...
Nigel
12/07/2020 04:48:54 UTC
Jon C said :-
Spark plug as requested. I had not cleaned the valves prior to re assembly last time.
I inverted the cylinder head and poured paraffin in (and obviously an old spark plug to seal that hole). It really didn’t drain quickly and 2 hours later the level has dropped a little (I’m guessing this is evaporation).
I’m just about to go and take off the valve retainers and measure the springs. This will let me then look into the back of the valves. I will check surfaces for an even level.
Posted Image
12/07/2020 05:56:04 UTC
nab301 said :-
I may be wrong but generally I would put the paraffin in the ports and see if it's leaking out the valve seat , maybe look into the ports after draining the paraffin from the combustion chamber and see if there's any sign of leakage , (dampness)
I posted this before ,a photo of the plug from my CB125F , the base of the plug is slightly cleaner but yours matches the online plug diagnosis photos for an ok plug.
NGK version here
https://ngksparkplugs.com/en/resources/read-spark-plug

Nigel
https://www.denso.com/global/en/products-and-services/automotive-service-parts-a...
Posted Image
12/07/2020 08:49:26 UTC
Upt'North said :-
Jon.
That head mating surface is a mess. You can get them skimmed but check it first as already suggested. The head gasket seems to have deteriorated quickly too unless it was like that in the first place.
You might be onto something.
The spark plug, is it new'ish? The colour looks good but the metal body seems to have lots of surface corrosion on it for a new plug, if that's what it is.
Good luck.
Upt'North.

13/07/2020 12:24:06 UTC
Jon C said :-
Thanks everyone, again!
Have ordered new head gasket and will check to ensure the head is level the moment I get some spare time. I am very tempted to just go and buy another since I have found the whole lot for 66 euros. Mon to Friday I have to work in London so can’t do a huge amount The spark plug is not new. It’s at least a year old.

Will post an update ASAP,

Jon
13/07/2020 02:26:55 UTC
ROD said :-
Not sure how bad the head is from the pics, but if it is not deep damage, a smooth finish can be achived with a sheet of wet and dry on a sheet of glass.
13/07/2020 06:13:37 UTC
Jon C said :-
Update. Spent an hour taking out piston rings and checking end gaps and they were perfect.
I then got a metal ruler and checked the head. There are parts of the head where the ruler sits perfectly flat but there are sections , Specifically around the most blackened part of the head, where I can see clear light passing through gaps. I don’t know what is considered acceptable as I guess the gasket is supposed to help form a seal. But I would guess that the height of the gaps is not much more tan 1mm.
Ill de-coke the head, clean up and measure again. I’ll double check for valve leakage and gaps.
20/07/2020 01:51:08 UTC
Jim said :-
Hi Jon - if you’ve got a 1mm or more gap then you have your answer. Even a tenth of that is likely to be an issue.

Cheers

Jim
20/07/2020 07:47:37 UTC
Ren - The Ed¹ said :-
It's my understanding that gaskets are there to take up the microscopic gaps so a 1mm gap sounds like a vast canyon! Can you post up an image or 3 of these gaps and how you're measuring them Jon C?
20/07/2020 08:23:14 UTC
Upt'North said :-
+2 on the head surface, it may skim but if not it's scrap by the sound of it unless you're not able to measure it flat on the surface yet due to the mess on there.
Upt'North.

20/07/2020 09:24:38 UTC
Ian Soady said :-
+3. I think we did point this out earlier - where did the gouges come from? Was it you or the person who fitted the big bore kit?

Given the state of it you're probably better going for the replacement head. I am quite surprised that you're obviously fairly handy with the spanners or wouldn't have been able to do the valve seals, but didn't think there was something amiss with the state of the head joint.
20/07/2020 10:51:55 UTC
Jon C said :-
Apologies for the radio silence. Been too busy applying for stuff. My cbt has now expired. I need to contact local training school about full exam etc.
Ian, my bike does not have a big bore kit. The head is like it is not from me. One of the previous owners must have been a wally and used some implement to get the engine opened. I’ve never had a problem in opening it.
So, regarding me not spotting the issue with the head. It’s about experience. I can follow instruction and carry out work, but if I’ve never seen what things are supposed to look like in the first place, I won’t be able to spot things like this without knowing that it’s not normal. I 100% thought that the previous owner had never opened the bike as it only had 6,000 miles, a clean hpi check and mot history. Now that you guys have indicated to me that the head is a disaster, I’ll know what to look for. It just happens that I got some arrears due to me paid this month. So I’ll buy the new head I showed you earlier. However, tonight, I’ll try to clean the current head surface a bit with and post pictures for your opinion.

Thank you again for lending your experience!
25/07/2020 08:36:14 UTC
Ren - The Ed¹ said :-
We are all here to learn. If you'd seen the mistakes I made as a younger mechanic you'd cry. And I'm still making mistakes.

Before you shell out on a new head it might be worth finding a local engineering shop who could give you a price to skim the head - and advise whether or not the head can be skimmed. I have absolutely zero idea of the cost as I've never had a head skimmed, perhaps the other readers can advise?
25/07/2020 10:12:39 UTC
Ian Soady said :-
You normally only skim a few thou to get rid of very minor warping / damage. If you go too far you will change the compression ratio and possibly upset the cam drive geometry. Those gouges and nicks look quite deep to me.

I'd go for the new head.
25/07/2020 10:31:24 UTC
Bob said :-
I would have said that if you're seeing 1mm warpage on the head face and gouges like that then is means someone missed a head bolt and was trying to pry the head off whilst still bolted on.
1mm is a HUGE amount of warp, you'll not get that skimmed back to true without drastically altering the squish and compression and possibly risk valves hitting piston crown.
I'd fit a different head.
One other thing to check. The oil scraper ring expanders should force the scraper rings out quite forcibly. I have seen in the past where people have rebuilt an engine and unable to get the rings back into the bore they have cut down the oil scraper ring expander. I'm mentioning this because there has been talk of blow-by, petrol in the crankcases and those valves look very oily - all of which could be caused by inadequate pressure on the scraper rings. If you can just wiggle the piston back into the bore then I would investigate further.
25/07/2020 08:15:28 UTC
Jon C said :-
Please see below link. Took a short video. Tried to put lamp behind to show gaps. Cleaned the surface first with Gentle wet sanding 400 grit just to get rid of obvious surface crud. Seems to me that there are gaps but your opinion would be great.

https://youtu.be/Gkn_o7EVY_M

Bob, the piston and rings and bore are brand new. I threw old the old piston and bore as there was obvious damage to the top ring and one side of the Piston and barrel.

Thank you everyone!
25/07/2020 11:16:31 UTC
Jim said :-
Hi Jon - certainly seems to be letting the light through, but it’s hard to tell how big the gap is. If you’ve got a set of feeler gauges, try getting the .10mm gauge under the ruler.
25/07/2020 11:24:50 UTC
Jon C said :-
Hello Ian,
Thank you for your quick response.
I do indeed have feeler gauges. So my previous estimates of 1mm before cleaning with some gentle wet sanding were way off.
I checked various cross sections and In the worst cross section I can get a gauge of 0.08mm in the gap but no bigger.
I would say however that there are some deep Individual nicks in the surface That concern me. I wonder what the previous owner did to leave such deep marks ? No matter. I’m not sure if I can proceed with this head and these obvious dents???
Posted Image
26/07/2020 01:14:58 UTC
Upt'North said :-
Jon,
At a wild guess he either cleaned the surface off with an axe or prised the head off with a crowbar (both not recommended techniques).
Upt'North.
26/07/2020 01:22:05 UTC
Upt'North said :-
I have found these to be excellent gasket scrapers. Not expensive either but totally idiot proof. I should know....
Upt'North.

Posted Image
26/07/2020 01:26:37 UTC
Jon C said :-
Upt’North these look useful. I’ll buy myself one.
So what do you think? New head? No way this head can be used? Although feeler gauge indicates not more than 0.08mm gaps. The individual ‘chisel’ marks are just too severe. Does anyone think that this is potentially what caused the compression in my engine to be 120 psi despite having a new piston and barrel? And the smell of overheating coming from under the tank when I re assembled the engine and did a test run.
A new head helps me also ensure that I have new valves and springs. So takes care of multiple points of potential concern.

Jon
26/07/2020 02:52:18 UTC
nab301 said :-
If the gap is no more than .08mm I would suggest the head is probably ok . The really critical bit is the round bit that seals the combustion chamber to the barrel. The markings on the head look to be a bit uneven in this area . Do you still have the most recent head gasket you removed ? If you had an accurate method of measuring the gasket thickness In the " fire ring " area(at different points around this ring) a micrometer would be best, but using a cheap vernier may allow you to see if the gasket has been clamped unevenly .
Nigel
26/07/2020 04:16:47 UTC
Upt'North said :-
Jon,
If you want to put it all back together fingers crossed, then fit a new gasket and see how it goes.... BUT, will you end up taking it apart again. Fit another new gasket and the new head and so on.
It's your call but it looks OK'ish to me. But the proof will be in the pudding.
The symptoms you describe could have been caused by this fault, I think the gasket looked really strange too, probably because of the leaking gasses.
It's your decision John, for the price of a head gasket and your time, is it worth a try?
Upt'North.
26/07/2020 05:11:30 UTC
Jon C said :-
Ok. Enough messing about. Am ordering a new head today.
Thank you everyone once again for your opinions. I think I was trying to really cheap out when I knew that I was never going to be really sure with this repair.
Your responses to seeing the 60 mile old gasket and the head, as well as these latest conversations, have brought things to a head (Pun intended).

Jon




26/07/2020 07:52:14 UTC
Jon C said :-
Hello everyone,
After much searching and deliberating this is Second hand genuine Honda a top end that I can get for £55.
Would you buy it?
Posted Image
05/08/2020 07:43:16 UTC
Upt'North said :-
Difficult to say from the picture, but it looks ruff. I'm a No.
Upt'North.
05/08/2020 11:22:24 UTC
Jon C said :-
Man. Really? The choices that I can afford are as follows:
1. Current head , cleaned and new gasket
2. The one pictured
3. A Chinese clone but new


05/08/2020 12:14:57 UTC
Bogger said :-
Looks ok to me. I'd go with it.

Bogger
06/08/2020 10:07:15 UTC
Bogger said :-
Looks ok to me. I'd go with it.

Bogger
06/08/2020 10:07:17 UTC
Jon C said :-
Bought it. Guess this will either be an expensive mistake or a great deal.

Thank you everyone,

Jon
07/08/2020 01:34:43 UTC
Ren - The Ed¹ said :-
Have you got it yet Jon C?
10/08/2020 08:14:40 UTC
Jon C said :-
Yes Ren, received Saturday. To the eye, looks a tonne better than mine.
Just need to find the time to clean things up and put the engine back together.

Jon
10/08/2020 05:47:26 UTC
Ren - The Ed¹ said :-
Fun fun fun! You'll be a CBF125 expert by the end of all this.
11/08/2020 08:37:42 UTC
Jon C said :-
Hello ! I’m back.
I’ve taken the second hand top end that I received and my old top end.
I took out the Valves and valve springs and measured both springs for exhaust and inlet valves on both engines.
I have found a disparity between my old top end the one I just bought.
Look at Haynes manual, valve spring free length should be 37.78 mm for outer spring and 37.30 mm for the inner springs.
My outer springs were over 1 mm out in my old top end from what I can tell.
Another thing I noticed is that the exhaust valve on the newly arrived top end has a hell of a lot of carbon deposits compared to mine and this is reflected in the actual valve seat.
Any opinions on what you see or what I have described ?
I’m going to clean the carbon deposits off and then do a leak test on the newly received engine valves.
Posted Image
16/08/2020 09:09:45 UTC
Ren - The Ed¹ said :-
In my opinion I'd take the longest of each spring (mostly from the new head) and use these. As for the carbon deposits on the new head it'll be worth checking the seat thoroughly but it suggests the bike it came from was running rich or had piston ring issues. As long as the head is flat and cleaned up it ought to be as good as you can hope for.
17/08/2020 08:08:50 UTC
Bogger said :-
Don't get too hung up on inconsequential crap. Bung it back together and ride it.

Bogger
17/08/2020 12:14:13 UTC
Upt'North said :-
Well said Bogger.
17/08/2020 12:43:26 UTC
Jon C said :-
Hello everyone,
Thank you very much for your help.
I apologise for taking up your time and for making you read my posts on inconsequential things. Whoever administers this site, please feel free to delete my posts.
Thank you again, I’ll complete the repairs with my Haynes manual and get on with it.
Cheers

Jonathan
17/08/2020 02:48:16 UTC
Upt'North. said :-
What Ed said plus clean the new valves up being careful not to mark the valve guide or seat area.
Wouldn't hurt to lap them in either.
Upt'North.
17/08/2020 04:10:46 UTC
Ian Soady said :-
Nobody is forced to read anything on here (other than Ren but then that's what you get when you start something....)

Don't apologise - everyone had to start somewhere. When most of us did we didn't have handy websites like this. We were lucky to have a 3rd hand manual, a bent screwdriver and a hammer.
17/08/2020 04:25:09 UTC
Upt'North said :-
You had a BENT SCREWDRIVER! I used to dream of having a bent screwdriver.
Although I've got a garage full now.
Upt'North.
17/08/2020 05:06:17 UTC
Bogger said :-
Jon C. I've read your last message a couple of times and I may have this wrong.

I'm not saying your postings are inconsequential. No, far from it. What I am saying is, don't tie yourself in knots going to the N'th degree worrying about issues that will not have a bearing on the end result. i.e a functional working engine.

Bogger
17/08/2020 10:16:51 UTC
nab301 said :-
@ Jon C , don't stop posting or asking questions , I don't look in here every day but on any forums i do log in to I generally just look at the technical sections . I find the questions interesting and if I think I can help I reply.
At the end of the day all anyone can offer is advice , back in the 70's as a teenager all I had was Motorcycle Mechanics magazine once a month which over time as an archive answered many problems for me, and local bike shops which drew varying responses ! In particular I had a Honda S90 with a slight noise from the cam chain . A relative suggested , be careful , the cam chain drives the oil pump ... Local bike shops suggested , it's fine son , that's a quiet one , in the end i stripped the bike and couldn't understand what the fuss was about , there was the camchain and some sort of a smooth jockey wheel , no problem .... until on closer inspection I realised that the smooth jockey wheel was the oil pump sprocket with no teeth ... after that I never stopped asking questions or investigating problems until I was happy .
As Ren said , fit the longest valve springs , maybe use grinding paste and then do a leak test , reassemble and hopefully you can ride off into the sunset / sunrise!
Nigel
18/08/2020 03:14:33 UTC

Post Your Comment Posts/Links Rules

Name

Comment

Add a RELEVANT link (not required)

Upload an image (not required)

No uploaded image
Real Person Number
Please enter the above number below




Home Repair And Restoration

Admin -- -- Service Records