Camchain and tensioner seen up close in a cutaway bike engine

Home Repair And Restoration

State Of The Engine Address

Job Date 15 to 31 August 2020

By Ren Withnell

I needed to investigate the rattle. 

I know, remove the rocker cover and see if the camchain is done for. Rocker cover off and pull on the camchain as it goes over the cam sprocket. The chain does lift but only the merest amount suggesting there's life in it yet. The tensioner and guides look in order too. Hmmmm. This does NOT preclude my suspicions of the tensioner being the cause of my woes but otherwise everything seems as I'd expect.

To coin a phrase made popular by a swords and dragons show, "Winter is coming..." This winter I plan to do the shims on the CB500 and I really could do with the 125 being "right" in case I require transport. Presently the 500 seems good so now is the time to do some real investigations into the state of the 125's internals.

I could just make a manual camchain tensioner, ride the bike and see what's what but no, no, I am going to be brave and strip down the top end. Oh lordy, oh sheez, my goodness, what kind of tomfoolery is this? Brace yourselves gentlefolk, I'm going in all spanners blazing. What fool am I?

Seat off, panels off, tank off and I'm ready. While I'm bigging this up the CBF125 engine is in fact very simple at the top end. Exhaust off, loosen the inlet rubber, 4 bolts and the valve train is off. 2 more and the head is off.

The camshaft, rockers and adjusters all in one unit
Self contained tappets. Perfect. Roller bearings too. 

What do I find? Dirt, as you might expect. After a great deal of cleaning beneath the dirt is the cylinder head. It all appears in order. While I'm here I compress out the valves.

Cleaning years of dirt off the aged cylinder head
Diesel and toothbrush. 

The valve stem seals are - n't. They are present but they're as hard as the steel they sit on. I replace them from the full gasket set I have purchased. The valves get a good clean. The valve seats look tired, pitted even. If this were a newer bike I'd take it to the engineer's and get new seats and valves put in but it's not. Instead I spend an hour lapping them then replace them. That'll do, "good enough for me".

The valve seats are dirty, worn and grimy
"Sub-optimal" would be my description.
The valve has a step in it where it meets the seat
Is the valve supposed to have a "step" in the seat face?
The seals look intact but they are as hard as metal
Hard as nails them seals, aka useless.

Next I remove the barrel. I have wondered if my rattle was piston slap, small end, big end or even mains. There's the merest smidgen of movement from the mains, the big end feels OK and the small end seems acceptable too. Nothing is what you might call "tight" but there's no discernible movement up or down. Maybe I'm not doing it right. Surely after this many miles *something* must be shot? I double check and while my fingers are not micrometers for this motor everything seems "good enough for me". 

I remove the piston. The top 2 compression rings come off easily but aha! The oil control ring(s) are gummed into place. This would explain the excessive oil usage, that and the valve stem seals. The correct route is to replace the oil control ring(s) and while I'm at it as they come as a set, replace the compression rings too. Don't be silly! This is me. Another hour or so of fiddling, spraying, prying and then cleaning the rings are "good enough for me".

The piston has some carbon on it and the oil control rings are gummed
I've seen worse. I've seen better too but still.

There's incredibly minor scoring on the piston sides, front and back, but again nothing of concern. The barrel, well, that's perfect. No lip at the top or bottom, I can *just JUST* make out the original cross hatching if I squint and stare really hard. Meh, sod it, it's all going back together. 

Inside the barrel there's no step in the wall
Not crosshatcing, just a light 1200 grit sanding. No lip though.

The worst part is removing the old gaskets. The worst part of removing the old gaskets is removing the old gasket from the base of the cylinder. Scrape. Brush. Bathe in diesel. Bathe in petrol. Scrape. Try burning it off with a blowtorch. Try burning it off in the oven. Worry about changing metallurgical properties due to excess use of heat. Scrape. Go to bed smelling of solvents. Scrape.

Scaping bits of very stuck on gasket from the base of the barrel
I HATE this job!
The base of the barrel is now perfectly clean and shiny
The fruit of my labour.

I rebuild the motor. Did you know the full gasket set for the CBF, either aftermarket or genuine Honda, does not include the gasket between the cylinder head and the inlet "rubber into metal" section? No? Neither did I. I shall now ask the masses - is Aldi Bran Flakes box cardboard or Aldi Red Label Tea Bags box cardboard better for a gasket? I have gone with the Tea Bags box cardboard. 

The gasket is sanwiched between the inlet tract and the cylinder head
Red Label gaskets.

Before I attempt to start it I convert the camchain tensioner to manual. 

The tensioner has been converted with a threaded M6 screw
Let's see how this works then.

It runs!!! In fact on first startup it is so very quiet it is surreal, after 10 minutes of smoky tickover a few rattles return as everything settles in once more. Smoky tickover? I greased the barrel once cleaned to prevent rust. I greased the piston rings to ensure they slide in properly. I even greased the cams to ensure lubrication until the oil gets all around. 

While the tank is off I notice the pipe from the tank to the fuel pump is baggy and loose. I purchase and fit a new 6mm bore pipe along with clamps to ensure I don't have a leak. 

The new fuel pipe is held in place with clamps
Better than new.

She's ready to ride folks. Wish me luck.

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Reader's Comments

Bogger said :-
All gummed up. You obviously didn't try the stuff I gave you. Harumph.

01/09/2020 02:22:39 UTC
Ren - The Ed¹ said :-
Once the motor's running again I was gunna give it a flush and synth oil as supplied. Thing is now I'm gunna need reminding what is in which bottle...
01/09/2020 02:57:09 UTC
Marv said :-
Nice work Ren! Hopefully what you've done will resolve the issue.
01/09/2020 03:17:27 UTC
Snod said :-
My money is still on the exhaust for the rattle :D
01/09/2020 03:55:52 UTC
Bogger said :-
Flush is in the flush bottle. Panel wipe in the small clear bottle. Oil in the oblong clear bottles.

01/09/2020 05:31:16 UTC
Jim said :-
Should be good for another 90k now Ren!
01/09/2020 05:33:34 UTC
Pocketpete said :-
omg ren, could you really not get a new set of rings.... poor engine no wonder its shouting at you on the overrun
01/09/2020 06:15:32 UTC
Bogger said :-
To be fair. For 90k it ain't too bad.

01/09/2020 08:14:10 UTC
Bob said :-
Did you inspect the rocker shafts and the roller cam followers?
They can cause a rattle.
Interesting that Honda use the roller cam follower design. I looked into cam follower types after one of my Vigors ate its camshaft.
As I understand it, when catalytic convertors and Lambda sensors came along ZDDP was removed from engine oil because the byproducts of burning it can foul these components.
ZDDP was added to oil to generate a protective coating on the surface of hard metal parts, specifically cam lobes and followers. With the ZDDP removed the old type of finger cam follower can suffer accelerated wear, because the load is always applied to the same place on every valve actuation.
Shim valve trains don't suffer because the bucket rotates in operation so there is distribution of the loading effect over time.
I ended up running ZDDP additive in my Vigors and SLR, the engines were noticably quieter on the top end.
The roller follower in the CBF addresses the problem too.
02/09/2020 09:58:36 UTC
Upt'North said :-
For what it's worth young Ed me lad, I agree with your rebuild methodology, it's an old tired engine, why go NUTS! I would think it as at least cured some of those oil burning woes, but them valves, what a mess they were in. I think other than a broken valve I've never seen worse.

02/09/2020 04:00:18 UTC
Ren - The Ed¹ said :-
Bob - I gave the cam bearings and rocker rollers (ha!) a wiggle - nothing smacked me in the face as being untoward. Interesting re the ZDDP. My old CB250T (1978) used to wear out the follower face where it meets the cam and not the cam lobes. I guess if a bucket wears out they'll be cheap enough to replace.

Calm down Upt'! An oil thread is always a source of endless fun (and fallouts and arguments). I'm glad to read that you approve of my methods, it helps me feel all warm and fuzzy inside. I did wonder if I should go the extra mile with the head but then I remembered I am tighter than a truck's lug nuts. Hmmmm, thinking on there, maybe that was the issue in the first place? I'm so tight I squeak on the overrun which I've misheard as a rattle from the motor?

Well I'm NOT spending any money to cure THAT problem! Pffffft.
02/09/2020 05:32:42 UTC
Bob said :-
Right, since this now officially and oil thread....

One of my KLX250s had started to use oil, over the course of 6 months, 6000 miles and 6 oil changes it would lose about 150ml between oil changes. So that's 150ml per 1000 miles.
According to the wisdom of the internet 150ml per 1000 miles is perfectly fine, but not for an engine that didn't use any previously and since the oil capacity is only 1300ml the level drop was annoyingly noticable.

So I started getting down about how the engine was obviously now wearing out. Then I remembered that I had bought two 4 litre jugs of 10W40 semi-synth JASO MA oil from Newark autojumble and I had been feeding the bike on that. I dropped the oil out and switched to lovely 10W40 full-synth JASO MA2 and now 3000 miles and 3 oil changes later it hasn't used any oil since I switched over.

So there you go - not all oils are created equal.
03/09/2020 09:19:44 UTC
Upt'North said :-
Oh gawd, pass the pop corn.
03/09/2020 09:35:44 UTC
nab301 said :-
Quote "Is the valve supposed to have a "step" in the seat face?"
NO !! other than that though it's in remarkable condition!

I've been using fully synthetic oil in all my bikes in recent years with zero oil consumption ( Enfield excluded!) and have found that if I revert to semi synthetic they tend to start using oil.
06/09/2020 06:01:16 UTC
Ren - The Ed¹ said :-
Well nab301 you will be pleased to hear - a certain Bogger from not too far from here passed some synthetic oil my way that seems to have fallen off the back of a truck. Alongside this was a bottle of engine flush. Since the rebuild I have flushed said engine as per the instructions on the bottle and the motor is now running on "fully synth".

I shall be monitoring my oil consumption. Unfortunately this may not be an entirely accurate comparison as we'll never know how much of the usage was down to bad/good oil or the once stuck now unstuck oil control rings and valve stem seals. Never-the-less I am fascinated to see how this pans out.
07/09/2020 08:13:17 UTC

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