'06 RM250 Piston Size

[Yamahauler]

Does anyone happen to know how to identify which piston is supposed to be used when replacing a top end in an '06 RM250? The parts catalog has two pistons listed. Part numbers are...12110-37F20-0F0 & 12110-37F30-0F0. I know Yamaha's have A,B,C & D size cylinders which have the letter stamped on the cylinder. I can't find any such reference on the RM.

 

[j32]

is it stock?
have the cylinder deglased/honed-to remove the crapp
then have it mic'ed and find out the bore size --- buy a wiseco piston,and rings
or by the book--- use a flatt feeler gage and place it in the cylinder between the piston and the cylinder,and see how much clearance there is
wiseco use a- 3 thousands between them,and relieve the exhaust bridge by wiseco's specs

 

[yellow725]

for 05 and 06 use 12110-37f30-0f0 the other # is for 03-04

 

[Yamahauler]

J32, yes the bike is stock. This is the first top end for this bike. I've always run OEM pistons and I don't have any experience with the WISECO kits. Do you have good results with WISECO pistons? I race hare scrambles and never had a failure with OEM parts (knock on wood).

Yellow, that's what I needed to know, thanks! Just looking in the parts fiche, you can't tell. I assume the rings are 12141-37F00 for 05-06 and 12141-37E02 for the 02-04 as well...correct?