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XR200 Prox 66mm XR200 piston

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Do you know if this is a cast or forged piston ? I'm going to get my cylinder bored to fit this one and it'll make a difference depending whether it's cast or forged.The Prox piston instruction sheet says to set the clearance to factory specs,but if specs are unknown,set it to .0025" clearance.The OEM XR200 clearance is less than that(from what I can find .0006-.0018")and I want to go about .001" clearance.

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Edited by grcamna5

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You can go with .001" no problem....

The vertex pistons are well made and have their metallurgy down pat for piston heat expansion..

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Cast usually have a lower expansion rate than forged which is why forged run at larger clearances. The only advantage I can see with forged is stronger and harder for less wear but stock cast seem to last forever in the little Rs. The the wear items are the rings which is another subject but dependent on; bore material, bore finish, lube oil, and of course operating conditions.  I've run XRs on OEM pistons for many years wo smoke or oil use, I bought a used 84 XR250R in 88 and sold it in 08.  In 82 I installed a Wiseco piston in a XR200R and ran that bike for a full decade of competition, some years logging more than a 1000-1500 trail miles. That engine still has good compression but hasn't had much run time this past decade. 

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1 hour ago, Chuck. said:

Cast usually have a lower expansion rate than forged which is why forged run at larger clearances. The only advantage I can see with forged is stronger and harder for less wear but stock cast seem to last forever in the little Rs. The the wear items are the rings which is another subject but dependent on; bore material, bore finish, lube oil, and of course operating conditions.  I've run XRs on OEM pistons for many years wo smoke or oil use, I bought a used 84 XR250R in 88 and sold it in 08.  In 82 I installed a Wiseco piston in a XR200R and ran that bike for a full decade of competition, some years logging more than a 1000-1500 trail miles. That engine still has good compression but hasn't had much run time this past decade. 

Chuck,Does this Prox piston look like cast to you ?

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