250r Piston Size

[spliffy]

I Have This 86 250r & I Am Going To Rebuild The Top End This Winter & I Am Wondering If I can Tell By Looking At The Top Of The Piston What Size It Is, The Guy I Bought It From Said It Was Rebuilt Once But Didn't Know What Size Piston Was Put In It. I Would Hate To Go All The Way Up to Like A .040 Or Higher To Be Sure That I can Bore It Out If It Has Only Been Bored Once So Far. Thanks

[airheadedduner]

It sould say on top piston size in mm. You should have the bore measured before you order a piston anyway. Sometimes the piston will wear the bore into an oval shape requireing you to bore it further, and somethimes it will be within tolerences and you can go ahead and put the same size piston back in. I always have the clyinder bored to the piston when I do a rebuild to make sure everything is perfect.

[spliffy]

Thanks! :)

[beerock]

have the cylinder size measures with a micrometer, or a dial bore gauge...

measure the piston with a mcrometer....

if the bore is more then .04 mm larger then the piston its time for a bore job..

BUT FIRST!

go the next size up on the piston and order the piston before you bore it. Most shops will ask for the piston.(if they do good bore jobs)

pistons vary slightly in size so its good to have the piston on hand so the bore size is made to fit the piston to exact specs.

[spliffy]

Thanks Beerock.... Would You Recommend Pro X Or Wiseco? I Mostly Do Woods Riding.

[beerock]

well, I am a fan of pro-x. because there cast and the expansion contraction rates are better then the forged weisco.

I only use pro-x

by the way pro-x is made by ART

ART makes genuine honda pistons and yamaha pistons....
the only difference is that pro-x makes pistons in large sizes.
I think honda only makes pistons up to the 4th bore....so getting a pro-x is like a honda :rolleyes:

[spliffy]

ProX it Is Then :macho