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Small engine mechanical help
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<blockquote data-quote="greybeard" data-source="post: 1415047" data-attributes="member: 18945"><p>Because an engine in good mechanical shape only produces slight changes in crankcase pressure + or - when running. A worn out engine (rings and cylinder wall) allows combustion pressure to leak by the rings and into the crankcase--combustion pressure is a lot higher than just the cranking pressure you get when doing a compression test due to the expanding gasses of combustion. Good rings, no scored cyl wall, good valve guides hold the combustion pressure on top of the piston where it is supposed to be so it can do it's work. Worn crap allows some of that pressure into the crankcase, and does it at a time when the piston is on it's way down, which shrinks the total volume of the crankcase.</p></blockquote><p></p>
[QUOTE="greybeard, post: 1415047, member: 18945"] Because an engine in good mechanical shape only produces slight changes in crankcase pressure + or - when running. A worn out engine (rings and cylinder wall) allows combustion pressure to leak by the rings and into the crankcase--combustion pressure is a lot higher than just the cranking pressure you get when doing a compression test due to the expanding gasses of combustion. Good rings, no scored cyl wall, good valve guides hold the combustion pressure on top of the piston where it is supposed to be so it can do it's work. Worn crap allows some of that pressure into the crankcase, and does it at a time when the piston is on it's way down, which shrinks the total volume of the crankcase. [/QUOTE]
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