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YZ125A cylinder

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Hi,

I have a 1990 Yamaha YZ125 that my grandson pulled off of a trash pile. It needed a lot of work, and now that we got it running, the water jacket in the cylinder has a crack. Cylinders are not available new. I found a few 1991 cylinders on eBay. Does anyone know if that will fit the 1990? The part numbers differ only in the prefix letters. I'm not sure what that means.

Edited by Gregory W Hillen

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It would fit just make sure the power valve matches the exhaust port. The magazines back in the day used to recommend putting the 90 top end on the 91. The 91 had some quality control issues with ports not matching to the power valve well. Same with the 92. 

Pretty sure 89 thru 93 would work with the 93 being the best. But you may need the cylinder head and power valve depending on the year. 

The 93 is the last year of the ypvs drum and the best setup. Yamaha moved the power valve to sit slightly closer to the exhaust port for better sealing. 

Also do yourself a favor and get a 91 - 93 aluminium clutch cover. It flexes less than the magnesium covers of the 89-90 and fixes the clutch drag issue. 

I do not remember if there's any issues with the exhaust pipe fitting i think the 89 is a one year only and 90 thru 93 should have the same exhaust flange.

Edited by SmokinJoe

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Thanks for that info. Very helpful. The search broadens. But worst case, one of the 91 cylinders looks pretty good. I'll look for a 93 for a few days though. On the clutch, I'm assuming you mean the internal cover over the basket. Not the external cover.

 

Thanks,

 

Greg

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Hello again,

 

I got a very nice 91 cylinder (56mm) and piston (56mm) only to discover that the power valve from the 90 won't work in the 91 cylinder. I found a few 93 power valves on eBay. Does anyone know what year power valves will fit in the 91 cylinder? I'm at a standstill until I find one.

 

Thanks,

 

Greg in  Colorado

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