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Another piston size thread. 1989 YZ250WR

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I recently bought a 1989 YZ250WR which has had the cylinder sleeved and bored to 68.50mm. I am not very familiar with sizing a piston to the cylinder. In the past I have always took it to the shop and had them order one for me, but I want to do all of it myself this time. I have searched the threads and found several conflicting stories. Also, when I look at factory pistons on a site like bikebandit, it does not show dimensions, it shows .25, .50. 75, and I am not certain on what size it would be. Thanks for any input.

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If stock is 68, you would use the 68.5. The question is sort of confusing, though. Most often shops bore to the specific piston, not the other way around.

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Nah, don't have the old piston, it was a basket case when I bought. Had already been sleeved and bored.

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+1

Give Wiesco a call and see what they recommend. You may need to send the jug and new piston for a fresh bore also. That way you know that the piston and cylinder will match up and you will also know what to order in the future.

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