Topic: strange noise, what is it?

[Jeremy]

ok, I'm a newbie and i'm not sure what this strange noise is coming from the bike(77 cb550). When it warms up after 15 mins of riding I can hear what sounds like a rattle, it seems to increase with rpm and goes away around 4000rpm. I only hear this noise under heavy load and at low rpm. Is this just a valve adjustment or am I into something more serious. Don't see any smoke.

[Harry]

Sounds like knocking (ignition too far advanced).

[Jeremy]

Ok, retarded the timing about 5 degrees and went out for a spin. Noise sounds like a diesel engine starting up, i think it must be valve noise. Could this be? I really only hear it when i have a passenger on the back and when I accelerate hard. 3 or 4 taps and it goes away. Seems  to get worse with load.

[kghost]

Sounds like you filled it with bad gas and its now detonating.

Recommend you drain the tank and refill with 92-93 octane and the see if it makes the noise.

Some people will undoubtably post that 87 octane works fine but, thats if it has not been contaninated or degraded.

[scondon]

Hey Jeremy,

       I'm guessing it's your cam chain, or your primary drive chain. Try adjusting your cam chain tension as per the manual( sorry, I ride a 750 so procedure may be different ). When you get on a bycicle and start pedaling from a stop(load) the top of the chain gets very tight and the bottom becomes loose and floppy. Same thing happens inside your engine and even on your drive chain. I've chased what I thought was "engine" noise just to find that my improperly adjusted chain was slapping the center stand. Hope this helps.

[Raul CB750K1]

scondon, same thing happened to me. Specially on bumpy roads, the loose low side of the drive chain was hitting the centerstand.

BTW, I also hear a strange noise on bumpy roads from the front end. It's kind of a metallic clack, like if the mudguard was loose, but it isnt. I put the blame on the brake caliper hitting the disk, but I can't know for sure. Have any of you noticed something similar?

Regards

Raul

[Jonesy]

If the final drive chain is really loose, it can smack the chainguard. I used to have an aftermarket chainguard on mine and even when the chain was a t the proper tension it would slap the gaurd when I let off the throttle.

[Gordon]

Raul,

I've experienced the same front end noise.  I think I traced it down to the caliper hinge that allows sideways movement.  Mine is just slightly loose, so when I hit a bump it moves up and down making that noise.  I could be wrong, but that's the only thing I found loose anywhere on the front end.

[Raul CB750K1]

Gordon, I did the same investigation and it was the only moving part that I found on the front end capable of making that clonking noise. I'm not worried about it anymore, but who knows...