Chatter Noise

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Mreece

Mreece

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Jul 6, 2017
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Hello everyone,

I have a 1973 Norton Commando that I have rebuilt from front to rear. The only component I have not rebuilt is the transmission, besides the outer cover where the kick-start is. My problem is this- when I am in gears 1st-4th under light throttle load or just cruising along, I can hear a chatter noise. Under hard acceleration or load it goes away, or at least I cant hear it and it sounds fine. I replaced my chain and that helped significantly but I can still hear something. It doesn't do it when I am stopped and or rev it up, and it also doesn't do it when I am going along and pull in the clutch lever.

Can it be something within the transmission? Possibly a bearing that it starting to go bad in it?

HELP!!!

Thank You!

-Mark
 
Does the noise change note with engine revs ie whatever the gear does it sound the same at say 3000 revs, or does it change note with road speed and is the same at say 40 mph regardless of gear.

If its related to engine revs then its clutch and forward into engine, road speed related then it could still be clutch but then gearbox and also back wheel including rear chain.
 
Thanks for replying Kommando,

I can definitely hear the noise more going along at a slower constant speed. The note of the noise I would say stays the same no matter what gear at a constant speed. But as soon as I go to accelerate at all, it goes away.

Thank You!!

-Mark
 
Kommando,

What are symptoms of a bad transmission? It shifts great and doesn't make any sort of grinding noises, other than the chatter.
Could the chain from my clutch to the transmission be going bad, or possibly not lined up right or to tight?
What other things should I look for before taking the transmission out and sending it to Colorado Norton Works and spending a bunch of money I might not need to necessarily do.

Thanks again,

-Mark
 
it is very difficult to diagnose 'chatter' are you sure it is from the gear box or primary drive?
 
If it were a timing chain or primary chain it would occur regardless of whether the bike is stopped or not. If it was a wheel or drive chain it should change relative to road speed. So I think the clutch and main shaft become suspect if it stays the same relative to engine RPM regardless of gear selected. However, are you sure it is rotational and not some part trying to rattle off?

Russ
 
Rvich,

I am positive it is rotational. I can be stopped in neutral or in gear with the clutch pulled in and rev the engine and not get any chattering until I am going at a constant cruising speed.

When you say main shaft, are you talking main shaft in the transmission?

-Mark
 
Oldmikew,

I believe it is coming from the gearbox, but it could also very well not be that and be the primary drive.

Like I said it only does it under a light load and under hard load it goes away.

-Mark
 
sometimes a loose primary chain will slap against the primary case particularly when you are off throttle and the chain unloads between engine pulses and causes a bounce in the chain. Check the primary chain for slack
 
Mark,
I would pull the primary chaincase outer and make sure all is well ... can you for instance rock the clutch body on the gear box main shaft? you ight have missed out spacers, has the mainshaft nut come undone etc... many years ago when i was youngMW had a chatter issue with my BSA Super Rocket...
because it did not do it on overrun I assumed the bigends were fine.. on start up it was ok under acceleration chattering rather than knocking... and then
the con rod pokes itself through the cases at 80mph. Interesting experience... i think what had happened was that a big end nut had backed off. In the naivete of youth had not replaced the bolts... Not saying this is your problem but it fooled me ... try and use a stethascope if you can get hold of one, or a long screwdriver and put the handle to your ear.. may help you to pinpoint where exactly its coming from..
 
Mreece said:
Rvich,

I am positive it is rotational. I can be stopped in neutral or in gear with the clutch pulled in and rev the engine and not get any chattering until I am going at a constant cruising speed.

When you say main shaft, are you talking main shaft in the transmission?

-Mark
Click to expand...

Yes, I was referring to the main shaft of the transmission. The reasons being that it rotates at a constant speed relative to the engine RPM. The output of the transmission changes speed with gear selection, so I would think this would change the sound when you shifted gears.

As someone mentioned it could be the primary chain making noise, but that chain rotates regardless of whether the bike is moving or not and so would only be the culprit if it was only making noise when tensioned by the clutch being engaged. This is possible. I suppose the clutch basket might behave differently when the clutch is engaged but it also rotates constantly. It is coupled to the main shaft so this area I would concentrate my efforts.

And yes, I am making wide sweeping guesses based on your senses. If the above logic doesn't make sense that is probably my failing and not yours.

Russ
 
rvich said:
Mreece said:
Rvich,

I am positive it is rotational. I can be stopped in neutral or in gear with the clutch pulled in and rev the engine and not get any chattering until I am going at a constant cruising speed.

When you say main shaft, are you talking main shaft in the transmission?

-Mark
Click to expand...

Yes, I was referring to the main shaft of the transmission. The reasons being that it rotates at a constant speed relative to the engine RPM. The output of the transmission changes speed with gear selection, so I would think this would change the sound when you shifted gears.

As someone mentioned it could be the primary chain making noise, but that chain rotates regardless of whether the bike is moving or not and so would only be the culprit if it was only making noise when tensioned by the clutch being engaged. This is possible. I suppose the clutch basket might behave differently when the clutch is engaged but it also rotates constantly. It is coupled to the main shaft so this area I would concentrate my efforts.

And yes, I am making wide sweeping guesses based on your senses. If the above logic doesn't make sense that is probably my failing and not yours.

Russ
Click to expand...

Most specifically I would look at the clutch hub first. You will get a look at the primary chain when you are there. If there isn't something found on the clutch hub, then move to the inside of the transmission.
 
Remove the Primary outer cover. Start the bike and observe the primary chain for slappings. Next step drive the bike ( no clothings to get slurped in ) and if chatter is louder then the issue is in the primary works. Otherwise the final drive chain may be the culprit. Sloppy or worn out. :?
 
Mreece said:
I replaced my chain and that helped significantly but I can still hear something.

-Mark
Click to expand...

It may still be the drive chain. They do make noise all on their own. More when old & worn, but always some even when sprockets and chains are all brand new.
 
My wife is usually quiet unless I do something stupid , then she belts me. Cant be that. Good guess though.
Dereck
 
You say you have rebuilt the bike front to back, Have you replaced the gearbox top bolt spacer on the correct side? it needs to go on the transmission side (LHS) not the timing side. It is possible with a bit of force to get this wrong (don't ask me how I know) and your primary chain will be a mile out of alignment and could give the noise to which you refer.
 
Also you say that you have replaced the chain but what state are the sprockets in. The gearbox sprocket is buried and easily overlooked, could be totally shagged out, check out the rear sprocket as well. Two chains and time for new sprockets IMHO
 
Hi,
I have a little chatter noise from the primary at slow cruising speed when the engine nearly not pulling, eg. when it's going slightly downhill. But that don't worry me much. The primary components are new and the chain is correctly tigthened.

Ralf
 
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