The piston should have a .25 on it if it's 1st. over or a .50 if it's 2nd over ... HPO identifies it as a TRX500FE/FM/TM piston ..On the TRX500 you measure the piston 15mm from the bottom of the skirt..
If you have a motor and it needs to be bored you must get the piston (whatever size you need) then take the piston & cylinder with the clearances you want to the engine or machine shop , that's the only way to be 100% sure the clearance will be right .. Honda also recommends that once it is bored the final hone should be done with nothing courser than #600 stones for max engine life..
If you want the 2005-06 piston/cylinder section from the Honda PDF shop manual just PM or post your email address ...
Here is a picture of a 1st (.25) piston for a TRX450 you can see the .25 etched into the piston top .. On this piston HNO means TRX450 model
If you have a motor and it needs to be bored you must get the piston (whatever size you need) then take the piston & cylinder with the clearances you want to the engine or machine shop , that's the only way to be 100% sure the clearance will be right .. Honda also recommends that once it is bored the final hone should be done with nothing courser than #600 stones for max engine life..
If you want the 2005-06 piston/cylinder section from the Honda PDF shop manual just PM or post your email address ...
Here is a picture of a 1st (.25) piston for a TRX450 you can see the .25 etched into the piston top .. On this piston HNO means TRX450 model
