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Over sized Piston?

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Over sized Piston?

PostAuthor: BryanM362 » Mon Aug 12, 2019 10:59 am

I am rebuilding a 1981 XV 920. I have the rear head and cylinder off. The piston is marked "25" (not .25). Does this mean it is bored 1 over? I think it does, but just want to verify before buying new rings. Thanks!

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Re: Over sized Piston?

PostAuthor: bstig60 » Mon Aug 12, 2019 3:30 pm

I would think it would be .25 mm oversize, or first oversize. Perhaps this will help.
https://www.cmsnl.com/help/faq/95_yamaha/#f391
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Re: Over sized Piston?

PostAuthor: Jake » Tue Aug 13, 2019 11:37 am

I deleted your duplicate post in “Tech”. You only need to post one topic per issue/problem. Multiple threads on the same topic will not get you faster or better answers, most likely just duplicate answers. If different solutions should be offered, it's better to have them on one thread.

If you don't get an answer in a reasonable time, reply to your own thread with "bump".
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Re: Over sized Piston?

PostAuthor: BryanM362 » Tue Aug 27, 2019 3:36 pm

BryanM362 wrote:I am rebuilding a 1981 XV 920. I have the rear head and cylinder off. The piston is marked "25" (not .25). Does this mean it is bored 1 over? I think it does, but just want to verify before buying new rings. Thanks!



This is solved. I had a machine shop measure the piston and it was .25mm over. So, a "25" stamped on top of piston does mean it is .25mm (1st over). 50 means .50mm (2 over), 75 means .75mm (3 over), and 1.00 means 1mm over (4 over).

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