What piston kit to get?

[TravEX]

This winter I plan on rebuilding my 250R. The motor is a ATC 85. I wanna do all that I can myself.

So, let's say the bore diameter is 67mm, do I order a 67mm piston kit? What if it's a little over or a little under XXmm, do you round up or down when ordering or have it bored up to the next mm?

Thanks

Travis

[Aceman]

I was under the impression you have the bore measured at it's present size, order the next size up piston and have them bore it to match the piston.

[TravEX]

K, thanks.

[QuadRacer18]

your better off simply taking the cylinder to get bored and having that company order the piston because they need to use it to get the best measurement with the rings and such when boring?honing cylinder.

[YFZRob]

Quad racer is correct. If you KNOW that your bore is well under 67mm, and you don't have any massive scaring damage to your sleeve, you can probably buy a 67mm piston, but make sure you provide the piston to the machine shop and let them size it to the bore. The final honing after the bore (if they even bore it) has to be done to your piston since you have to be within 1-2 thousandths of an inch to the piston spec (like .004" clearance).