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All you have to do is take the head off and fill the port with brake cleaner.(either intake or exhaust) Then look at your valves in the combustion chamber for any leaks. If so take a drill and grab the top of the with the chuck and spin the valve until it feels smooth and spin in both ways.(A small cordless drill works the best)Finally refill with brake clean and test for leaks. This worked prefect on my gy6 83cc with a ported 50cc head. Lots of compression now the valve seats are good.
 

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on mine i grabbed a second set of valve spring shim fro ma donor yx150 type engine and double shimmed my valve springs.
 

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All you have to do is take the head off and fill the port with brake cleaner.(either intake or exhaust) Then look at your valves in the combustion chamber for any leaks. If so take a drill and grab the top of the with the chuck and spin the valve until it feels smooth and spin in both ways.(A small cordless drill works the best)Finally refill with brake clean and test for leaks. This worked prefect on my gy6 83cc with a ported 50cc head. Lots of compression now the valve seats are good.
Hmm.....That's not a valve job.....hell that's not even lapping if your not using lapping compound. Also using a drill and chucking directly to the tip of the valve is a HORRIBLE practice.

A valve job is when angle(s) or radii are cut or ground into the seat via machine

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Or can be done with neway hand cutters
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What you are attempting to do is called lapping. When lapping compound (which comes in a variety of grits) is placed on the valves seating face as seen here
Floor
The valve is inserted back into the head and spun on the seat. The more common route to perform this action is with a lapping cup
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There are mechanical power lappers out there but they are pricey and not practical for the backyard dyi guy. For the dyi guy that wants to lap mechanically a drill can be used but.... As stated before chucking directly to the tip of the valve is a horrible practice and there's a laundry list of potential things the cam go on. The safe and easy on ur head/valve way to do it. Would be find a piece of tubing that fits really snuggly over tip of valve then chuck drill onto tubing (not valve stem) then give her hell
 

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what's the difference between spinning it with a wooden handle and a drill? it's still going round and round. EDIT: i suppose with a cup one might spin it back forth.
 

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what's the difference between spinning it with a wooden handle and a drill? it's still going round and round. EDIT: i suppose with a cup one might spin it back forth.
Your grabbing the stem of the valve with the drill which is not good practice
When using the proper tool your not harming the valve at all.. Just touching the "combustion chamber" part of the valve
 

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When I replaced valves on my crf 50's "race head", I used a drill, but from a guide I found online, I used a small piece of tubing that held the valve tightly, like 2 inches long, then the other piece of the tube went over a screw that was chucked in my drill. I used lapping compound however.

/old post I know, but looking up gy6 info and found this thread
 
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