I'm doing a top end rebuild. Previous history is pretty much unknown. The piston is stamped " 38A "
At this point I'm not sure sure if that's s standard or over bore. In the past with other machines I have always known what bore size was at and would always order the next piston size up, drop the piston and cylinder off at my machine shop and they take it from there.

 

38A is a stock piston. Plus if oversize it would say .25 or.50 if oem.

 

83.00 mm is a standard bore if you wondering

 

Thanks for the info...I'm currently looking for a service manual so without it, even general specs is unknown.