This question is just a general question that I need another mechanic to help me answer. I pulled apart a 99 KX80 because it had no compression, and not only was the cylinder scored and the piston shot, but i noticed some excessive wiggle on the bottom end of the connecting rod (over the bearing). I can actually get some vertical play out of it as well. How much, if any, is acceptable? Thanks in advance -Randy

 

The rule of thumb is that if you feel any movement, the crank needs to be replaced. However, on your KX, the radial clearance on the big end of the con rod should not exceed 0.09 mm which is quite common spec on most 2-st engines. On my 1990 2-stroke jetski, the max limit is 0.10 mm. That should be measued using a dial gauge and placing the crank/con-rod assy on a V block. If you keep riding with that, you will experience more damage such as requiring cyl, case, etc. replacement later. Check it out.

 

Thanks. That "if you can feel it, replace it" is what I have always been told too. I've already got the motor out and I guess I'll start looking into the price of new bearing assemblies, as well as another cylinder or at least new sleeve. I appreciate your response.