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Piston rings on a 50cc moped engine

This is a discussion on Piston rings on a 50cc moped engine within the Small Engines forums, part of the Tech Support Forum category. I am rebuilding a 50cc 2-stroke moped engine and i need to replace the piston rings. i measured one of


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Old 08-08-2008, 06:22 PM   #1
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I am rebuilding a 50cc 2-stroke moped engine and i need to replace the piston rings. i measured one of the existing rings and it reads about 41mm in diameter. I went to the website of the company and found all the technical information about the moped and it said the piston ring diameter was 32 x 2 as you can see in the first picture. I don't know what units they are using and I cannot order the exact parts online because the company went out of business. The company is called JAWA and is from Europe. I need the correct measurements of the ring so i can order a new one. 32 x 2 is the only information given and if that is in millimeters, then it argues with my 41mm reading of the ring diameter (it is most likely not exactly 41mm but i don't have the correct tools to measure accurately). Are they measuring it a different way? Please tell me what i should do when trying to order replacing piston rings. I was thinking of using rings used for chainsaws. The cylinder has not been re bored. Also, on the second picture i do not understand why there is "A,B,and C" measurements of the same piston? Please help me.

http://img354.imageshack.us/img354/838/123he8.png
http://img125.imageshack.us/img125/1053/1234vt8.png

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Old 08-09-2008, 07:55 AM   #2
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You more than likely measuring the rings with them being out of the cylinder. The munufacturer is probably giving the dimension of the ring in an installed or "compressed" condition. Squeeze the ring until the ends meet and remeasure.

Best of luck.
SABL

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Old 08-09-2008, 08:40 AM   #3
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Your measurement of +/- 41 seems to be correct. After looking at the pdf @ jawa I would think that the 32x2 is a typo.....and probably isn't the only one. As for the 3 different measurements, those could be tolerances for taper at differing locations.

That is one crude tech manual!
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