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Piston size question

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Hello all, looking to do a top end on my YZ250 sometime soon (stock bore). Looking around Rocky Mountain and Motosport, it appears that I cannot select what size piston...from my understanding there is a, b, c, and d correct? Is this something that just applies to OEM pistons? I was looking at Wiseco and Vertex on both sites, and they only offered one size. Thanks. 

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16 hours ago, Shooter88 said:

Hello all, looking to do a top end on my YZ250 sometime soon (stock bore). Looking around Rocky Mountain and Motosport, it appears that I cannot select what size piston...from my understanding there is a, b, c, and d correct? Is this something that just applies to OEM pistons? I was looking at Wiseco and Vertex on both sites, and they only offered one size. Thanks. 

Yes, only applies to the OEM pistons,  as long as your cylinder is within service limits, any quality replacement piston should be fine.

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What year is the bike? I ask because they are stamped on the back and you might still have that visible. So if it is stamped C or D, I would not put in an A:66.34 and would put in a C or D 66.36-66.37, they say standard bore is 66.40 

Vertex can be had for 100 bucks in all 4 sizes on eBay. 

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i have seen aftermarket pistons (pro-x) with A B C and D designations as well as +0.50 and +1.00 sizes. since wiseco is forged it needs more clearance, therefore 0.01mm is not as much of a big deal on a forged as a cast piston which rides very tightly in the bore.  

Edited by MCRIPPPer
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2 hours ago, 2 STROKE YZ DOC said:

What year is the bike? I ask because they are stamped on the back and you might still have that visible. So if it is stamped C or D, I would not put in an A:66.34 and would put in a C or D 66.36-66.37, they say standard bore is 66.40 

Vertex can be had for 100 bucks in all 4 sizes on eBay. 

The bike is a 2006 and the marking on the cylinder is long gone. I never thought of looking around ebay...I'll definitely do that. 

Thanks for the replies everyone. 

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