Cylinder Question

[jski]

I recently melted the exhaust side of the piston on my CR-500 and at first thought I had a leaking crank seal and was ready to try to replace the seal but I just got off of the phone with the shop that is checking the bore on the cylinder and he informed me that the bore is egg shaped and is out .008 in general and is also out .020 at the exhaust port bridge. What could cause this a bad bore in the first place or thermal expansion and contraction of the materials at a different rate?

So now I have to go .040 over to clean it up and fix the cylinder. The cylinder has a thick sleeve installed and has been ported so I will fix it but I am wondering if the melted piston was caused by the out of roundness of the cylinder or if the crank seal is indeed bad? I think I will change the seal anyway because there was a few particles from the ring and piston in the bottom end and besides splitting the cases how would I get it out.

Thanks

 

[spanky250]

The excessive wear on the exhaust side of the cylinder can be caused by a loose rod bearing. I would bet on an air leak causing the melted piston.

 

[Freeride2002]

Another thing to check out is if the sleeve was improperly installed, there might be little air gaps between the sleeve and the cylinder surface. If this is the case the bore will develop hot spots and will cause the condition you mentioned.