Home
Repair And Restoration
CBF 125 Alternator-Stator Problem
By Ren Withnell
In short - No lights on the CBF 125 will typically indicate a problem with the stator which is part of the alternator. Also consider the regulator rectifier.
Details.
With no sign of anything amiss I rode the bike to work that morning. When I came back to the bike in the evening I started it up and I noticed a strange noise immediately. It is a hard noise to describe, the best I can do is to is image a man making that spooky ghostly "ooooooooo" noise but monotone. The pitch rises and falls with the revs and is quiet, background to the everyday engine noises. Then I noticed the lights were not working.
I considered the starter motor was stuck. I considered the flywheel was loose on the crank. I considered a failing bearing. I negated the starter motor by removing the whole starter mechanism but the lights did not light and the noise remained. The flywheel was secure on the crank, it must be as the flywheel also feeds the crank position sensor without which the engine would not start. I knew because of the lights the problem was at least in part electrical which pointed to the alternator.
By removing the stator from the system I started the bike and the noise had gone. It HAD to be something to do with the stator. While all the electrical tests showed no problems the lack of lights and the noise from the stator meant it HAD to be the stator. I was sure. Sort of. Sure enough to spend £116 for a new stator from Honda. And while I was at it I also got a new regulator rectifier as the pair work hand-in-hand and if one breaks it often breaks the other.
I fitted these items and the bike works fine now, it feels great.
Explanation - Alternator, Stator, Rotor
An alternator creates electricity by passing magnets around coils. In the case of most motorcycles the magnets are attached to the end of the crank in a "bowl", known as the alternator rotor. The coils are fixed to the engine case, they stay still, but sit inside the spinning "bowl".
An alternator rotor. The magnets actually run all the way around the inner face of the "bowl"
The stator. This sits inside the spinning rotor and stays still.
So the magnets are spinning around the wires that are wound up into coils on the stator. Due to some weird electromagnet stuff when magnets pass coils of wire electricity is "induced" into the coils. This electricity is used to charge the battery, light the lights and power anything like fuel pumps and engine control units which are actually small computers.
Explanation - Regulator Rectifier
The alternator makes electricity. Unfortunately not quite the sort of electricity your motorcycle needs. Firstly when the motor is running slowly it makes a bit of electricity. When the motor is revved up it makes a lot of electricity. To run your lights, computer, fuel pump and digital clocks it might take 150 watts. At tickover the alternator might only make 100 watts so the battery has to provide the rest. But at 8,000 revs it might make 300 watts and that's too much! The regulator esentially "dumps" the excess power as heat.
The electricity from the alternator is AC, alternating current. It's far too complex to explain on this simple page the whys and wherefores but your bike uses DC, direct current. The job of the rectifier is to convert the AC from the alternator into DC that the battery and the rest of the components use.
This is a VERY simple explanation of the regulator rectifier. It's actually a simple device doing a very complex task. If you need more details you'll find them online.
A typical "Reggy Reccy". Notice the fins to cool it when it "dumps" the spare electricity.
Why Replace Both?
Why did I replace both the regulator rectifier AND the stator? Because I'm not an electrical genius that's why. If the stator breaks due to a broken wire or a short, the reggy reccy might receive far too much electricity and get fried. If the reggy reccy breaks it might ask the stator for too much electricity and overheat the coils. I'm making guesses here but what I do know is that when one breaks it can cause the other one to break as well.
Far smarter people than me with clever equipment will know exactly how the alternator and the reggy reccy work. They may also have the equipment to test each item, find the exact fault and make sure everything else is working. I however don't have access to that knowledge or equipment. I didn't want to spend £116 on a new stator only for the old reggy reccy to burn it out in a few weeks.
Reader's Comments
Harry said :-
hi there, just had the very same problem with my bike. not replaced the stator yet, but the new regulator is in there, i just like you said. im no genius, and its better i started at the cheaper part and then go to more expensive part (the stator) becuase its worth replacing both parts.
30/08/2016 13:14:20 UTC
Ren - The Ed said :-
Hi Harry. I hope you get it sorted out. I've seen quite a few posts on forums and across the internet similar to mine so it seems a common issue.
02/09/2016 06:03:21 UTC
said :-
04/10/2017 17:11:28 UTC
Rocky said :-
My side,head,main and tail light stopped working and took out the alternator and it had 3 points which had burnt out could this be the reason the main lights won't work.
12/11/2017 22:43:15 UTC
Ren - The Ed said :-
Hi Rocky. It sounds to me that the alternator is your issue. It's also worth checking your regulator rectifier too and the wiring.
I do not have a specific method of being 100% sure it is the alternator, you'll need the help of a professional for that. Thing is they're not too cheap so it's certainly worth exploring all angles before you make your purchase.
13/11/2017 14:02:52 UTC
Ben said :-
Today morning I tried to turn the bike on and it was dying all the time. I pushed it down the road, putted on second gear and finally managed to turn it on. Then I've heard a lot of explosions coming off my custom exhaust; at first I kinda liked it, but soon the bike died again, leaving me walking all the way back home.
Changed the battery and spark plugs, didn't make a difference. Then a friend told me it should be the alternator. Unfortunately he was right. The coils were all burned.
Do any of you know why they got burned?
17/04/2018 21:49:39 UTC
Ren - The Ed said :-
Hi Ben. Welcome to the world of the dark arts.
If you look on any forum regarding this subject there are as many opinions as there are people. Some say "too much load" others "old engine oil" others "failing battery" others "excessive heat" others "crap build quality" others "general wear and tear" others "failing regulator/rectifier" and so on and so on.
So no, I don't know why your coils burned but I do know mine have burned out twice so far, once at around 30,000 and again at around 59,000. If you manage to find the everlasting coil please be kind enough to share them with us!
18/04/2018 07:43:05 UTC
kieran vernon said :-
got a cbf125cc when i do 55ish i get a loud groaning noise that stays till i drop below 3k revs so when i hold the clutch in and no revs at speed noice goes away it seams to be 7k+ revs it kicks in sounds like chewbacca but its not the engine im thinking eletrical i dont get it at any other speed only 55+ still have lights ect ect what could this be ive tryed revving the bike for a min ro see if i ca get the noice but i carnt irs really annoying lol shouting at me
18/03/2019 12:42:37 UTC
Ren - The Ed said :-
That's a new one on me Kieran. My alternator made a spooky "oooooo" noise, quite quiet. That said I didn't get chance to ride it at pace.
I don't have an answer for you. As a matter of safety though check your tyres, wheels, chain and sprockets.
19/03/2019 08:41:54 UTC
Upt'North said :-
+1 Ed, are you sure this is rpm related and not road spedd related. If road speed you need to be looking elsewhere. Perhaps post more details.
Can it be replicated in other gears.
Can it be replicated at standstill.
Is the chain correctly adjusted and lubed.
Is the vehicle serviced.
Upt'North.
19/03/2019 09:59:05 UTC
Ren - The Ed said :-
Yeah we'd need more details. I am tempted to suspect the alternator but there's quite a few other more important safety items I'd go through first.
19/03/2019 11:14:17 UTC
McBert said :-
Cbf 125 not running unless connected to power supply/jump leads, drained new battery, felt heat coming from regulator rectifyer is this normal, but bike not starting no ignition lights nothing even getting to fuel pump
Please help need advice??...
12/01/2020 14:10:49 UTC
Ren - The Ed¹ said :-
Fit a new battery. When fitted does the bike start? If yes then check how much charge is getting to the new battery. If there is little to no charge coming to the battery stop using the bike because you'll kill the new battery. Find out why it's not charging.
Broken wires? Regulator/Rectifier dead? Alternator stator dead?
I'd start with broken wires - check for continuity from the alternator through the reggy reccy and thence to the battery. The Haynes manual offers several checks for the reggy reccy but from experience these results are often at best inconclusive. I've always just replaced them but if anyone reading has any advice I'd be all ears. The alternator windings, as shown above, have a habit of burning out and if this is the case then all you can do is replace them.
13/01/2020 09:31:24 UTC
Neftali said :-
Hi Can you help?How can i know how much wire a stator needs...what would happen if i put more uneven...i have a Honda Cbf 125.
Please help and thank you
22/04/2020 19:41:26 UTC
Ren - The Ed¹ said :-
Neftali - first let me explain I'm no expert! I have considered trying to rewind my old stator but while I don't like spending money a replacement stator isn't TOO expensive. However I don't know your circumstances, it might be worth your time.
I have no idea how much wire is used. You would have to unwind the old wire so I'd take a measurement from that. I don't know the science but I do know that if you have more or less windings this would effect the output voltage and current. I would therefore recommend you make a note of the number of windings around each coil and how each coil runs (is wired) into the next coil.
Rewinding a coil can be done by the DIY mechanic, but it is a task that requires careful planning and equally careful execution.
23/04/2020 08:23:29 UTC
Bob said :-
Be careful. I tried this years ago with a KE175 stator.
I carefully counted the number and direction of turns, used a micrometer to measure the wire diameter and bought the correct size replacement wire.
It took all weekend to rewind it by hand, applying the layers, fixing in place and then connecting the terminating wires.
I refitted it to the bike - the result was everything blew, my new stator was pushing over 100V at tickover.
No idea what I did wrong.
23/04/2020 09:09:14 UTC
Ren - The Ed¹ said :-
OH NO!
23/04/2020 09:58:50 UTC
Neftali said :-
Thank you very much!
12/06/2020 20:07:28 UTC
Jamie said :-
When replacing the stator is it necessary to drain the oil first?
12/05/2021 13:26:19 UTC
Ren - The Ed¹ said :-
Jamie - Not necessarily. IF...if you can get the bike leaned over to the right hand side then most if not all the oil will stay in. On the centre stand you'll lose some but not all. However - for the sake of a litre of fresh oil just drain it out.
12/05/2021 16:44:57 UTC
Marc said :-
Hi my CB125F / GLR125 has developed an issue the lights became dim, it started but when I stopped i didn't start again, changed the rectifier and charged the battery, but still have the same issue, can anyone help.
02/02/2022 07:01:56 UTC
Upt'North ¹ said :-
Marc,
You've done the obvious things but have you checked the voltage at the battery.
Standing.
Charging.
Starting.
I'm not going to type out what you might expect at the terminals because it'll be on YouTube, everything is. I suspect your battery is toast and or stator. By doing the voltage check it'll point you in the right direction. Another alternative is just to fit a new battery and see what happens. I'm guessing they're not expensive and readily available. Just because a battery will charge doesn't mean it's OK. It means nowt really.
Is the battery old.
Has it been discharged many times.
Has it run dry, if not sealed, but I guess it is, doesn't mean it isn't dry though.
Have you checked, cleaned and tightened battery terminals and other earth terminals if present.
Good luck.
Upt'North.
02/02/2022 09:29:16 UTC
Marc said :-
Hi
Thanks for the reply, I initially broke down and the recovery metered the battery once he started it and the battery had very little volts going back into it once started, he told me to start with the rectifier, I brought the bike in 2018 with the battery on the bike already, not sure how long the battery has been on the bike as its reg is 2015 and I haven't replaced it, terminals all cleaned and reconnected, may have to try a new battery trying to avoid the stator as the bike is not worth to much anyway.
02/02/2022 09:49:10 UTC
Upt'North ¹ said :-
Good luck Marc, it's got to be worth a try.
But.........it's beginning to look like the stator.
But....... bad batteries can do strange things. Electrickery.
Upt'North.
02/02/2022 10:47:48 UTC
Ren - The Ed¹ said :-
The battery at rest should be AT LEAST 12v, preferably 12.6v
With the bike running the battery should be receiving around 14v.
With regards it being the Stator - I can not comment on the CB125F but my earlier CBF125 has been fitted with a pattern alternator. This has run since 2016 and covered around 35,000 miles. I'll add a link for more details.
https://bikesandtravels.com/biker.aspx?ride=954...
02/02/2022 14:38:43 UTC
Marc said :-
HI
Can does anyone know the torque setting for the stator bolts on 2015 cb125f and the torque settings for the stator engine case, don't want to over tighten
14/02/2022 18:56:50 UTC
Ren - The Ed¹ said :-
Hi Marc. My Haynes manual says "Crankcase bolts - 12Nm" - this is for 09 to 12 models. I cannot find a specific torque for the stator bolts but being the same M6 thread into the same ally material I'd suggest 12Nm would be a fair guess. 12Nm is around 9 foot pounds or pounds feet...
14/02/2022 19:55:24 UTC
nab301 said :-
The '09 to '17 Haynes manual suggests 12Nm for the alternator stator bolts .
14/02/2022 20:35:35 UTC
marc said :-
Thanks all for the help much appreciated.
14/02/2022 20:48:56 UTC
Michael said :-
Hello, I have a 2018 Honda CB125F that hasn't been used for about a year, and hasn't been used over it's lifetime very much (< 500 miles!). I went to turn it on a couple of days ago and wouldn't start, no lights or anything.
Purchased a smart battery charger from Halfords which complained about the battery being unrecoverable, so I checked the voltage and it was around 3.5V. So rather than buying a new battery I picked up a jump starter which allowed me to start the bike, however it shuts off as soon as the jump leads are disconnected. I left the leads on for 10 mins and check the voltage of the battery and it went to 6V so I'm thinking the battery's not dead?
I'm wondering if my issue is the alternator-stator or just a very undercharged battery? Anyone have any ideas for me to try before I attempt to swap the alternator-stator?
Thanks
12/10/2022 11:52:03 UTC
Ian Soady¹ said :-
I'd suggest the battery has had it. If it's been left discharged for any length of time - which it sounds as though it has - then it's unlikely to recover.
12/10/2022 13:36:34 UTC
Upt'North ¹ said :-
Like Ian says, change the battery, and DO NOTHING ELSE for now.
Once a battery becomes severely depleted you'll struggle or never recover it.
Upt'North.
12/10/2022 13:38:54 UTC
Ren - The Ed¹ said :-
Anything below about 11.5v is unrecoverable so 3v - you've no chance! As previously stated - get a new battery!
Once the bike is started and running you should see the battery charging at around 13v or more - you might need a few revs on to see this voltage.
Once the bike is running and you are happy with it - CHANGE THE OIL! At 500 miles it'll still have the running in oil in it so get that changed with fresh good quality 10w40 motorcycle oil. Then within the next 2000 miles be sure to check the tappets. Repeat the oil change and tappet check every 2,500 miles.
12/10/2022 19:59:36 UTC
Michael said :-
Thanks for the suggestions guys, I'll pick up a new battery tomorrow and let you know how it goes!
And thank you for the oil change suggestion, sorry this is a bit of a noob/silly question, can you just use any engine oil or is there a specific one more suited for bikes?
14/10/2022 15:56:31 UTC
Michael said :-
Sorry just re-read the above and saw your 10w40 recommendation, I'm going to pick up some Castrol 10w40 oil, thanks!
14/10/2022 16:37:44 UTC
Upt'North ¹ said :-
Use motorcycle oil of the right SAE.
Do NOT put car oil in a bike, unless you like a slipping clutch.
Upt'North.
14/10/2022 16:38:09 UTC
Ren - The Ed¹ said :-
The right and proper advice to a novice rider is to recommend a motorcycle specific oil for a motorcycle and the Castrol 10w40 is just the ticket.
You will learn Michael that motorcyclists can and will argue the merits and pitfalls of countless brands, viscosities and additives till the cows come home. I believe some of them would even go to war to defend their beliefs that brand X and viscosity y is right for YOU and YOUR bike.
Personally I've been running my CBF125 on Halfords cheap 10w40 car oil for 90,000 miles. But the fellow readers and contributors hereabouts all agree I'm a tight miser and a mechanical assassin.
Stick with what the manual recommends - it's likely Honda probably know better than a million plonkers like me who think they know.
14/10/2022 23:18:33 UTC
Michael said :-
Haha thanks all - just wanted to pop back on and say thanks for the advice, bike is starting perfectly with a new battery! Currently doing an oil change!
Thanks for sharing your wisdom :)
15/10/2022 08:49:32 UTC
Ian Soady¹ said :-
The only problem with "car" oil as far as I know is when it contains friction modifiers. These are usually indicated by a special symbol (which I can't find). They also conform to JASO-MB specification. JASO-MA should be fine.
There's quite a nice explanation in the link.
https://www.motorcycle.com/products/best-motorcycle-oil...
15/10/2022 10:39:48 UTC
Ren - The Ed¹ said :-
As Upt' points out the friction modifiers (really slippery stuff) can cause motorcycles with wet clutches to suffer from clutch slip. However with the staggering power from the CBF125 this never was an issue for me. Either that or my cheap oil didn't actually have friction modifiers.
Good work Michael. I hope you and your velocipede enjoy many miles together.
15/10/2022 18:36:19 UTC
Upt'North ¹ said :-
You make an interesting point Ed, in that the cheapo supermarket oil probably hasn't got slippery stuff added and as long as it's not marked energy conserving then you'll probably (?) get away with it. There is a lot of folk that use good old fashioned diesel oil in bikes abd seem to get away with it too.
Upt'North.
16/10/2022 09:49:17 UTC
Ian Soady¹ said :-
Just because I accused you (well hinted anyway) of stopping in a passing place, no need to ascribe my wise comments to that bloke in Northumberland.
16/10/2022 16:48:09 UTC
Ren - The Ed¹ said :-
Upt' pointed out the clutch issue with friction modifiers but he didn't specifically note the problem is due to said friction modifiers. You are both wise but you know how to use proper words Ian, that Northumberland bloke has only just moved on from "ug".
I would suspect 10w40 is 10w40. The differences come from the countless additives. Slippery stuff for modern cars that are trying to achieve good fuel economy, detergents for dirty (mostly diesel) engines, various soft metals to hopefully fill in microscopic gaps in worn engines, and magic unicorn dust for marketing purposes.
As we already know there are a million keyboard geniuses out there like myself who know very little but have read 2 articles and seen a YouTube video and are now experts. Here's one tip I hope we can all agree on. While the correct oil for you vehicle is that which your engine manufacturer recommends - if your engine runs on 10w40 then any 10w40 is better than NO 10w40. And change your oil!
17/10/2022 19:52:20 UTC
Shane said :-
I have a cbf 125, I’m having a problem with the lights, when I turn the bike on I have no lights working but when I rev it light start to work, I have changed battery n regulator still the same I have tried to bypass it and rewire the lights but it kills the battery
27/07/2023 02:24:56 UTC
Ren - The Ed¹ said :-
Hi Shane - do the indicators works OK? I'm guessing so if the bike starts.
There are 2 circuits on the CBF125 - one for the lights fed from one half of the single phase output from the alternator and one for "everything else" (Computer, indicators, fuel pump, injectors, etc) that runs from the other phase. It is common for these bike for the lights to be a little bit dim at tickover, but the should still be working quite well even at tickover. If you've replaced the regulator/rectifier then I'd be looking at the alternator.
Before buying the expensive stator coils check the wires from the coils for breaks and chaffing causing a slight short. Follow these wires to the regulator/rectifier too checking them for damage. Also ensure there's a good earth on the bike - Honda uses green wires for earth.
27/07/2023 18:27:32 UTC
Name
Comment
Add a RELEVANT link (not required)
Upload an image (not required) -
Uploading...
Home
Repair And Restoration