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General Minitrail Talk
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88cc Engine Rebuild Question
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<blockquote data-quote="69ST" data-source="post: 185575" data-attributes="member: 5"><p>Lapping, without cutting...or at least verifying condition...of the valve seats, bad idea IMHO. It can work out for the short term, too often it doesn't even last that long. If there's any pitting in the valve seats, compression will bleed-off. If there's any size/angle mismatch between seat and valve, then either sealing will be a problem from the get-go...or will become one far sooner than normal. The contact band, on the valve face, doesn't have to be perfectly centered and the perfect width but, achieving that with a rebuild gives the best shot at a long service life.</p><p></p><p>You really should check compression. At the minimum, turn the engine over via the kickstarter, by hand. Full compression should stop you dead when the compression stroke is reached. If it's hard to figure out when the compression stroke has been reached, compression is way down.</p><p></p><p>It doesn't take much to foul points. In my experience it doesn't usually take much to clean them either...a few passes with 600-grit and cleaning solvent. There has been one constant, though...weak, yellowish, spark. If you're getting nice blue-white spark with audible snap to it, I seriously doubt the point contacts are fouled.</p></blockquote><p></p>
[QUOTE="69ST, post: 185575, member: 5"] Lapping, without cutting...or at least verifying condition...of the valve seats, bad idea IMHO. It can work out for the short term, too often it doesn't even last that long. If there's any pitting in the valve seats, compression will bleed-off. If there's any size/angle mismatch between seat and valve, then either sealing will be a problem from the get-go...or will become one far sooner than normal. The contact band, on the valve face, doesn't have to be perfectly centered and the perfect width but, achieving that with a rebuild gives the best shot at a long service life. You really should check compression. At the minimum, turn the engine over via the kickstarter, by hand. Full compression should stop you dead when the compression stroke is reached. If it's hard to figure out when the compression stroke has been reached, compression is way down. It doesn't take much to foul points. In my experience it doesn't usually take much to clean them either...a few passes with 600-grit and cleaning solvent. There has been one constant, though...weak, yellowish, spark. If you're getting nice blue-white spark with audible snap to it, I seriously doubt the point contacts are fouled. [/QUOTE]
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88cc Engine Rebuild Question
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