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What size piston do I need?

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I pulled apart my 250 and want to drop a piston kit in it. The diameter of my cylinder is 67.3 mm. Do I want the exact same size replacement or do you adjust the size for movement? Thanks all.

Someone correct me if I am wrong but I think it would be a good idea to measure the piston too. It sounds standard bore. The smallest bore it states in the service manual is ~67.80.

 

Are you using a bore gauge?

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A bore gauge would be more accurate. You should measure in at least 3 different places down in the cylinder. Service manual will tell you the tolerances you need to have. Good luck

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Rust on crank JB weld holding case together. Is this a time bomb I need to let go of? My piston and gaskets shipped! DOH!!! Would it be cheaper to find a new motor or part it out? I bought the whole bike for 350. Thoughts?

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It would be cheaper to split the cases and check everything out. A new crank and bearings may be all that you need.

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Rust on crank JB weld holding case together. Is this a time bomb I need to let go of? My piston and gaskets shipped! DOH!!! Would it be cheaper to find a new motor or part it out? I bought the whole bike for 350. Thoughts?

 

What year is the bike? What is the condition of the rest of the bike (suspension, brakes, tires, plastics)? How many hours have you put on it? What is the history of the bike? Why are you doing the top end? That would determine letting it go.

 

Most likely it is gasket maker/yamabond sealing the cases as no gasket goes between.

 

The rust in the crank case would scare me. Might be okay if the rust never got to the bearings but rust means that water got in. I would split the case, send out the crank to be rebuilt for piece of mind.

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Are you capable of rebuilding this yourself? If so, go for it. I love working on bikes. If you have the time and the skill then jump in. Of course if the rest of the bike is roached then maybe reconsider and get a different bike.

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Yep the frames a 98 is this worth the trouble? These sell running for about 800 bucks around here.

 

Answer me first:

 

What year is the bike? What is the condition of the rest of the bike (suspension, brakes, tires, plastics)? How many hours have you put on it? What is the history of the bike? Why are you doing the top end? That would determine letting it go.

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