quote:Originally posted by Art Stephens:
...How do I do a leak down test and what will it tell me? ...
A leak down test fills a cylinder with pressurized air via the spark plug hole, with the piston/crank set initially at TDC on the compression stroke (when the valves are closed). The air flows through a small orifice to control the flow rate, and the amount of back pressure is read on a gage, which indicates the amount of leakage in that cylinder. Excessive air leakage can be heard hissing, either in the crankcase, the exhaust or the intake, giving a mechanic an idea what the source of the leak is. The crank can be slowly rotated to find bad spots along cylinder walls, oil can be pumped into the cylinder to determine if the leak is mostly past the rings. It is a very informative diagnostic tool for a mechanic. It goes way beyond a compression check in the amount of information it can provide.
below are some links to read:
http://www.xs11.com/tips/misc/misc3.shtml
http://www.racerpartswholesale.com/long29.htm
http://www.longacreracing.com/instructions/text/73010_PI_p.pdf#search='leak%20down%20tester'
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