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Difference between revisions of "Poppet valve"
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Although better heat conductors, aluminum cylinder heads require steel [[valve seat]] inserts while cast iron cylinder heads often used integral valve seats in the past. | Although better heat conductors, aluminum cylinder heads require steel [[valve seat]] inserts while cast iron cylinder heads often used integral valve seats in the past. | ||
Because the valve stem extends into lubrication in the cam chamber it must be sealed against [[blow-by]] to prevent cylinder gases from escaping into the [[crankcase]]. A rubber lip-type seal ensures that excessive amounts of oil are not drawn in from the crankcase on the induction stroke and that exhaust gas does not enter the crankcase on the exhaust stroke. Worn valve seals are characterized by a puff of blue smoke from the exhaust when pressing back down on the accelerator pedal after allowing the engine to over-run, such as when changing gears. | Because the valve stem extends into lubrication in the cam chamber it must be sealed against [[blow-by]] to prevent cylinder gases from escaping into the [[crankcase]]. A rubber lip-type seal ensures that excessive amounts of oil are not drawn in from the crankcase on the [[induction]] stroke and that exhaust gas does not enter the crankcase on the exhaust stroke. Worn valve seals are characterized by a puff of blue smoke from the exhaust when pressing back down on the accelerator pedal after allowing the engine to over-run, such as when changing gears. | ||
===Valve position=== | ===Valve position=== | ||