engine noise CR250 96

[michaeltaz]

Hi. I need advice/help please! I have a 96 CR250RT. I had the cylinder of and could feel no play when I pulled and pushed on the conrod. I only had the side thrust play of conrod on the big end bearing. Main bearings also no play. Piston like new. When I accelerate under load, I hear rattling, like a piston slap or like a car being in to high gear (like noise of the valves when engine is labouring). When there is no load on motor it doesn't make that noise. Only under heavy load and feels like it is loader in the mid range and fades when the revs are very high or very low. Can it be the crankshaft (big end)? How can I test it? Since I cannot feel any play? Must I replace the complete crankshaft/conrod assembly?

 

[IndyMX]

perhaps you should measure the piston skirt to cylinder wall clearance, and see if your over limit. Also I'd look into having the cylinder measured for size and roundness.

Could be that your piston and cylinder are done.

 

[2strokerfun]

Might be detonation.

 

[jsantapau]

Might be detonation.

that's what I am thinking

 

[michaeltaz]

Thanks guys. I changed my chain and exhaust springs and no improvement. I always used 93 leaded with a 32:1 TTS mixture and suddelny this. Now I used 95 unleaded with same same ratio and mix ..... and it worked. So it must have been detonation. Now I still hear it sometimes, but not near as much as before. I was so sure its the crank.
Thanks alot guys.