Clinician
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tomos nitro 50
Posts: 9
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Joined: Aug 19, 2011 19:48:09 GMT -6
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Post by bababoom18 on Aug 19, 2011 20:29:03 GMT -6
i just bought a big bore kit for a gy6/qmb139 50cc engine. my question is can i use the stock valve head with a 72cc cylinder without causing damage to the piston or head.?
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Post by jhbietz on Aug 19, 2011 21:51:04 GMT -6
In my experience you won't have any problems. If you want to be absolutely sure you can use modeling clay on top of the piston to be sure. Just put a small amount of the clay on top of the piston, install the gasket and head then rotate the engine one full revolution by hand. Disassemble the head and check the clay to see how much clearance you have. Not really necessary in your case. The only time I have went that far is when I milled the head and didn't use a gasket between the cylinder and the crankcase.
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Post by Bashan on Aug 20, 2011 5:21:01 GMT -6
Listen to JH Bababoom18, he does this for a living and knows exactly what he's talking about. Actually, everybody around here knows that and I wouldn't have had to say it but I've never had a chance to type "bababoom18" before. Rich
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Clinician
Currently Offline
tomos nitro 50
Posts: 9
Likes: 0
Joined: Aug 19, 2011 19:48:09 GMT -6
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Post by bababoom18 on Aug 20, 2011 9:14:27 GMT -6
thank you that helps alot- one more question- the big bore kit came with a standered 72cc head but no egr-can i use it and eliminate the egr tubing without modifing the carb.?
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Post by Alleyoop on Aug 20, 2011 9:59:22 GMT -6
Yes, actually those EGRs are a pain if they don't work right and you can get rid of all the extra hoses and canisters.
Alleyoop
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..BAD TO THE BONE..