[Doug997]

I recently rebuilt a 2001 Yamaha YZ125 and I continue to get a lack of compression and the bike will not start. I have replace the piston and ring with OEM parts. The bike had a different crankshaft and did not take the OEM top connecting rod bearing. I wonder if the connecting rod is too short and not allowing for a full stroke therefore giving me a lack of compression

Any suggestions would be helpful

 

[jaguar]

either that or a head gasket leak or the rings just not broke in enough yet to perfectly conform to the bore