This is a new L.A. Sleeve Forged piston kit for the original Honda and PRO-X ATC-250R 85-86, TRX-250R 87-89 BIG BORE to 310cc, 2-Stroke. The kit is supplied with the big bore 73.50mm size piston, rings, wrist pin, clips. This would be the +.060" oversize from the original standard bore. 

The standard bore size for the ATC-295R to TRX-310R is 72.00mm. This piston kit is the 6TH oversize, +.060"  big bore size  to fit a 73.50mm bore.  CHECK YOUR BORE SIZE BEFORE ORDERING!!

Your Honda cylinder must already have the big bore kit already installed to use this piston kit. (Year model 87-89 uses a .190" base plate with this piston.) The PRO-X Big Bore also starts at 72mm. A qualified mechanic should inspect your cylinder and measure your bore size before you purchase. 

A qualified machine shop is required to bore your cylinder to fit the piston. Hint: If an oversize piston is required buying 2 sizes larger than your bore is best to clean up the bore.

 

Note: Picture is the exact model, you will receive when ordering the following:

1 each piston kit part# W845P6

 

******Identification reference: This piston is for the PRO-X big bore cylinder or the original Honda cylinder that has already been big bored to the 310. Some call it the 300 or 295 . This piston fits 73.50mm bore.