1974 CB125 engine noise | GTAMotorcycle.com

1974 CB125 engine noise

eng2007

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best heard as clicking/clacking around 0:45 on the left side of the motor.

Bike has sat since 1976 until this year when I finished cleaning up the rest of it.

[video=youtube;hgYNP2kLdgs]https://www.youtube.com/watch?v=hgYNP2kLdgs[/video]
 
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I thought it was the cam chain as well due to the irregular 'slapping' sounds but Ive got the tensioner tightened past maximum in this vid (to the point where I wouldnt be able to lock it down with the locknut) but it still makes the same sound.

Ive had the rotor off to get to the tensioner mechanism and inspect it and it seems fine. Apparently on these bikes the tensioner is prone to failure but mine still seems to operate fine. These old actually deflect the guides themselves to take slack out of the chain.
 
it may still be cam chain, you could be maximum tight and still getting slop because its just worn out. The fact you can go past max makes me think that.
 
You tried to check if the thudding noise lessens when the clutch is engaged. The high pitch noise is your valve adjustment.
 
I purchased chain on the assumption that since the bike has only 4600miles it was just the 38years in storage that stretched the chain, especially since its a small, single-link type so hopefully the guide is not worn.

In this particular model, the chain tension is adjusted by deflecting the guide itself with an adjuster screw which is pivots on.

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I purchased chain on the assumption that since the bike has only 4600miles it was just the 38years in storage that stretched the chain, especially since its a small, single-link type so hopefully the guide is not worn.

In this particular model, the chain tension is adjusted by deflecting the guide itself with an adjuster screw which is pivots on.

View attachment 37144

And parts 4 and 8 will likely be grooved or so brittle from age that when you reassemble it the noise will persist. For a few bucks more, do it all.
 
My engine is a 74cb550. I did a top end overhaul and those things are solid. Are you 100% sure its the chain tensioner and not the clutch plates?
 
I will try replacing the cam chain first since I dont have to remove the head for that.

Why would the clutch plates make slapping noises?
 
at 4600 miles you shouldn't see loose clutch plates, but stranger things have happened.

Any idea why it was parked up 38yrs ago? just abandoned or had a strange rattle?
 
I suppose its different to access the clutch plates for you as the bigger cc bikes are on the side. The reason im saying this is because its also a common noise heard in then 550 fours. And by engaging the clutch at neutral, the noise dissipates. Of course the best way about it is the timing and the plate replacement.

Its been mentioned how aftermarket timing chains are not as good as oem and they fail and snap
 
Chains dont just stretch from sitting, theyre made of metal. Its likely either the cam chain tensioner is worn out or more likely, seized up and not actually tensioning. You'd have to open the engine to have a look at whats going on.

Either that or its a normal noise, its really hard to diagnose problems from a cell phone video because the sound is garbage. I dont really hear anything wrong from your video tbh, maybe it sounds like a problem in real life. Old honda small displacement engines are just noisy though, and have lots of ringing and metal on metal and hollow clanking noises, thats just how they are, especially if youre used to listening to newer bikes which are almost silent comparatively.

Im going to just assume you checked valve clearances, the valves chatter a lot when theyre even slightly out of spec.
 
The good thing is that you've got valve inspection covers on top of the head. Makes checking the valve clearances easy.
 
I thought it was the cam chain as well due to the irregular 'slapping' sounds but Ive got the tensioner tightened past maximum in this vid (to the point where I wouldnt be able to lock it down with the locknut) but it still makes the same sound.

Ive had the rotor off to get to the tensioner mechanism and inspect it and it seems fine. Apparently on these bikes the tensioner is prone to failure but mine still seems to operate fine. These old actually deflect the guides themselves to take slack out of the chain.

while engine idles (do not rev up) are you are loosening the lock nut and BACKING OFF the the tensioner bolt until cam chain sound goes away - usually less than one full turn or so, while the engine is idling? then turn in tensioner bolt, and as soon as you feel any resistance stop, and tighten the locknut. check to make sure your not doing it *ss backwards!

cause it sounds to me like you are - (as you described above). do you have a manual? please tell me you haven't started taking the motor apart, because the way you adjusted the cam chain was incorrect. it is highly unlikely that your low mileage engine would need the chain or sliders replaced. i hope you haven' done any damage to the tensioner mechanism while cranking in the tensioner bolt.

ps when you back off the tensioner bolt do not back it out so far that the bolt comes out and the tensioner parts fall off inside the engine. idle the bike , back off that tensioner bolt until it can turn without resistance, and you will HEAR THE ENGINE quiet. then turn in the tensioner bolt until you feel resistance -stop immediately there and tighten the lock nut. done.
 
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Clutch will make a helluva racket when idling in neutral...
Simply pull in the (properly adjusted) clutch to temporarily remove all the thrashing/clattering.
Speaking of clutch, yours will be trashed!
35-year-old clutch plates will be SOAKED through with oil, completely sponged. Garbage.
Requires only about five years (not 35) heheh...
1974 CB125, wow, amazing! Looks pretty clean.
Sometimes I miss my 1973 CB750. Great old bikes.
Hey I'd be real surprised if camchain slippers etc. are still available for it...
Good luck bro.
 
Any idea why it was parked up 38yrs ago? just abandoned or had a strange rattle?

It was parked due to front end damage. The forks were bent when I got it and it had numerous other issues, but not engine related. The strange thing is this noise hasnt heard when I first starting riding the bike about 100 miles ago. I have been flogging the engine though (190lb rider on 10HP motor) so maybe that has something to do with it.

Jimsun said:
And by engaging the clutch at neutral, the noise dissipates. Of course the best way about it is the timing and the plate replacement.

Its been mentioned how aftermarket timing chains are not as good as oem and they fail and snap

Noise doesnt change in neutral with clutch in or out, unfortunately. Its safe to assume that after 4600 miles the original OEM chain is in there. The replacement I ordered is NOS Honda.

bobjohnson said:


Chains dont just stretch from sitting, theyre made of metal. Its likely either the cam chain tensioner is worn out or more likely, seized up and not actually tensioning. You'd have to open the engine to have a look at whats going on.


Either that or its a normal noise, its really hard to diagnose problems from a cell phone video because the sound is garbage. I dont really hear anything wrong from your video tbh, maybe it sounds like a problem in real life. Old honda small displacement engines are just noisy though, and have lots of ringing and metal on metal and hollow clanking noises, thats just how they are, especially if youre used to listening to newer bikes which are almost silent comparatively.

Im going to just assume you checked valve clearances, the valves chatter a lot when theyre even slightly out of spec.


I think youre incorrect about the metal stretching. Have a read on 'creep' on Wikipedia about long-term metal deformation. Lets not forget that this chain was under tension for 38 years.

Secondly, turn the quality up to 720p and you will distinctly hear an especially loud chain slapping noise on teh left side of the engine around 0:45 and at then 0:55 and 0:58 when I rev it. Its quieter in most of the video but always there. It's quite loud and simply doesnt sound natural, especially because of its random nature. Ive heard this motor runnign on other bikes and it didnt have this nose.

Yes, the valves are adjusted.


boyoboy said:


while engine idles (do not rev up) are you are loosening the lock nut and BACKING OFF the the tensioner bolt until cam chain sound goes away - usually less than one full turn or so, while the engine is idling? then turn in tensioner bolt, and as soon as you feel any resistance stop, and tighten the locknut. check to make sure your not doing it *ss backwards!

cause it sounds to me like you are - (as you described above). do you have a manual? please tell me you haven't started taking the motor apart, because the way you adjusted the cam chain was incorrect. it is highly unlikely that your low mileage engine would need the chain or sliders replaced. i hope you haven' done any damage to the tensioner mechanism while cranking in the tensioner bolt.

ps when you back off the tensioner bolt do not back it out so far that the bolt comes out and the tensioner parts fall off inside the engine. idle the bike , back off that tensioner bolt until it can turn without resistance, and you will HEAR THE ENGINE quiet. then turn in the tensioner bolt until you feel resistance -stop immediately there and tighten the lock nut. done.


I've gone through the procedure as per the manual and tried various positions of the tensioner. I've pulled the right engine case and alternator to expose the tensioner and made sure it was working properly as I've read that these have problems because there is only a small circlip deflecting the tensioner so its a lot of force coming down on that circlip but it was fine. I've only backed out the tensioner bolt further than maximum to see if it would help with the noise. I couldnt tell whether it made a difference or not.



Gryphon said:
35-year-old clutch plates will be SOAKED through with oil, completely sponged. Garbage.


Can you tell me more about this? Im not having any slipping issues just that the clutch engages a little suddenly when taking off in first gear while in the 'friction zone'.



Thanks everyone for help so far.
 
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