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SN95 Cobras
Valve Stem (heads) Issue?
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<blockquote data-quote="Tabres" data-source="post: 15858458" data-attributes="member: 8059"><p>No, they are two separate tests.</p><p></p><p>A compression test is done by hooking a gauge up to a cylinder through the spark plug hole, cranking the engine over and measuring how much pressure the engine builds in that cylinder. You want to do it for all cylinders. The reading can tell you several things. You're looking for consistent values across all cylinders. Low readings in one specific cylinder might indicate a bad valve. Low readings in two adjacent cylinders normally suggests a head gasket issue. Low compression in several cylinders would indicate worn piston rings.</p><p></p><p>A leak down test, instead of measuring how much pressure the engine makes like during a compression test, measures an engine's ability to hold pressure. With a special spark plug fitting, while the cylinder is at TDC, you introduce compressed air into the cylinder. Normally when there are issues you'll hear the air escaping somewhere. Out of the intake manifold/throttle body would indicate a bad intake valve. Air out of the exhaust pipe/manifold is obviously a bad exhaust valve. Out of the PCV or areas like the oil filler cap is normally piston rings. Air bubbles in the coolant typically is a bad head gasket or cracked cylinder head.</p></blockquote><p></p>
[QUOTE="Tabres, post: 15858458, member: 8059"] No, they are two separate tests. A compression test is done by hooking a gauge up to a cylinder through the spark plug hole, cranking the engine over and measuring how much pressure the engine builds in that cylinder. You want to do it for all cylinders. The reading can tell you several things. You're looking for consistent values across all cylinders. Low readings in one specific cylinder might indicate a bad valve. Low readings in two adjacent cylinders normally suggests a head gasket issue. Low compression in several cylinders would indicate worn piston rings. A leak down test, instead of measuring how much pressure the engine makes like during a compression test, measures an engine's ability to hold pressure. With a special spark plug fitting, while the cylinder is at TDC, you introduce compressed air into the cylinder. Normally when there are issues you'll hear the air escaping somewhere. Out of the intake manifold/throttle body would indicate a bad intake valve. Air out of the exhaust pipe/manifold is obviously a bad exhaust valve. Out of the PCV or areas like the oil filler cap is normally piston rings. Air bubbles in the coolant typically is a bad head gasket or cracked cylinder head. [/QUOTE]
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Valve Stem (heads) Issue?
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