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What size piston for a yz125

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I picked up a nice cylinder that has crosshatching and doesn't have much wear and it doesn't have a stamp on it so I was wondering if I could put a 54 mm piston in it

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Just now, Ian Arnold said:

I picked up a nice cylinder that has crosshatching and doesn't have much wear and it doesn't have a stamp on it so I was wondering if I could put a 54 mm piston in it

Measure the bore, then you will know. 

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11 minutes ago, P84ONE said:

Measure the bore, then you will know. 

I don't have a guage and it's a 2005 so could I run anything between 53.95-54 and be ok?

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5 minutes ago, Ian Arnold said:

I don't have a guage and it's a 2005 so could I run anything between 53.95-54 and be ok?

Best get a gauge, mic bore. You can rent from an auto parts house. 

Best to have a manual, and tools to perform any work. You will need a torque wrench also to put it back together.

You will need to measure ring gap and need a feeler gauge also. 

So, to simply say, I could run anything between XXX-XXX and be ok, I can't answer. 

Maybe someone else on here will give you an answer. So hang loose, and wait. 

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48 minutes ago, P84ONE said:

Best get a gauge, mic bore. You can rent from an auto parts house. 

Best to have a manual, and tools to perform any work. You will need a torque wrench also to put it back together.

You will need to measure ring gap and need a feeler gauge also. 

So, to simply say, I could run anything between XXX-XXX and be ok, I can't answer. 

Maybe someone else on here will give you an answer. So hang loose, and wait. 

He said stock bore so I'm guessing a 54 will work

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Buddy, you are missing the point. "Stock bore" is 4 sizes. If the engine has an A size piston coming out, and you put in a D size piston you might be 2 big and as it expands it will lock. On the other hand, if it is a D size piston coming out, and you put a A piston in, you will possibly have piston slap and wear the skirts prematurely. 

An answer to get you a piston today: Vertex piston size B would/could/"B" a size that would work for you.

Pull out the piston, take it to an auto house parts store, and ask them to mic it. 

But I would measure before you buy.

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14 hours ago, P84ONE said:

Buddy, you are missing the point. "Stock bore" is 4 sizes. If the engine has an A size piston coming out, and you put in a D size piston you might be 2 big and as it expands it will lock. On the other hand, if it is a D size piston coming out, and you put a A piston in, you will possibly have piston slap and wear the skirts prematurely. 

An answer to get you a piston today: Vertex piston size B would/could/"B" a size that would work for you.

Pull out the piston, take it to an auto house parts store, and ask them to mic it. 

But I would measure before you buy.

I agree - except, to be clear, measure the cylinder.  

There was a recent thread about this. Without open that can of worms again, the Engineers who designed the engine and wrote the manual say measure the cylinder and use the matching piston. 

I take my cylinder into the shop to get it measured. Then I order the piston from the shop so he makes some money and hopefully is still around next time i need something like that done.

You can do it yourself with the correct equipment and skills, but the average person with borrowed tools wont get it right.

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38 minutes ago, Woodzi said:

I agree - except, to be clear, measure the cylinder.  

There was a recent thread about this. Without open that can of worms again, the Engineers who designed the engine and wrote the manual say measure the cylinder and use the matching piston. 

I take my cylinder into the shop to get it measured. Then I order the piston from the shop so he makes some money and hopefully is still around next time i need something like that done.

You can do it yourself with the correct equipment and skills, but the average person with borrowed tools wont get it right.

Yah, I ment to say "Cylinder" as his first post had said he got a new one with cross hatching and needed a size. 

Thanks for the catch!

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