Maintenance & Technical > KX250 / KX125

crank noise

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mustangfury:
When the engine on my bike is running, there is a tapping noise that comes from the crank area.  It could be from the clutch or the transmission.  I am not sure what it is.  It does it when the bike is in neutral and in gear. The tapping increases with engine speed.  It is a very light sounding tap but it is still there.  Sometimes it is louder than others.  The best way i could describe it would be to take and run the plastic handle of your toothbrush across the rollers on your chain fairly quickly.  The noise is not coming from the cylinder. I don't know if this is normal transmission noise or if there is a problem. 

There is no slipping in the clutch. I had the clutch apart about a year ago and everything in there looked like it was just out of the shop.  The gears do not grind when shifting and the bike shifts very smoothly. there is no performance issues, i just want to be proactive on a possible future problem.  I don't know if some bearing is wearing out or something. 

Any ideas?

thanks,
Stang

dirtjunkie85:
It may be your crankshaft bearings starting to go out. i cant think of anything else that it could be really. Maybe something in the tranny? what does the oil look like when you change it??

mustangfury:
the oil is just dirty looking.  I didn't see any metal in it.

BDI:
It is my experience that the kx500 has a noisy crank at idle and just off idle. The noise goes away if you pick the rpms up. It is also my experience that the noise the crank makes gets louder when you crank up the compression on the engine. The power valves also make noise on these bikes, especially when the power valves have just been cleaned. It is not uncommon for people to rebuild their top end and then have your complaint. I have also seen alot of people that don't ride their bike for an extended period of time trip out on the noise their kx500 makes just because they forgot how there bike sounds. I wouldn't worry about it unless it is a new noise the bike just started making.

mustangfury:
how do you check if the crank bearings are worn?  Can you check it when you rebuild the top end? also, if the crank bearings are worn, will that cause bigger problems if you continue to run the bike, say, till the next top end rebuild?

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