Leak-down readings of up to 20% are usually acceptable. The meaning of the readings is only relative to other tests done with the same tester design. Leakage is given in wholly arbitrary percentages but these “percentages” do not relate to any actual quantity or real dimension. This can be as simple as a breaker bar on a crankshaft bolt in an automatic transmission vehicle, or leaving a manual transmission vehicle in a high gear with the parking brake locked. Leak-down tests tend to rotate the engine, and often require some method of holding the crankshaft in the proper position for each tested cylinder. Pressure is fed into a cylinder via the spark plug hole and the flow, which represents any leakage from the cylinder, is measured. Testing is done on an engine which is not running, and normally with the tested cylinder at top dead center on compression, although testing can be done at other points in the compression and power stroke. Any test should include both compression and leak-down. Leak-down will not show valve timing and movement problems, or piston movement related sealing problems. Leak-down primarily tests pistons and rings, seated valve sealing, and the head gasket. Cranking compression is a dynamic test of the actual low-speed pumping action, where peak cylinder pressure is measured and stored. Compression tests should normally be done with all spark plugs removed to maximize cranking speed. JSTOR ( February 2015) ( Learn how and when to remove this template message)Ī leak-down tester is a measuring instrument used to determine the condition of internal combustion engines by introducing compressed air into the cylinder and measuring the rate at which it leaks out.Ĭompression testing is a crude form of leak-down testing which also includes effects due to compression ratio, valve timing, cranking speed, and other factors.Unsourced material may be challenged and removed. Please help improve this article by adding citations to reliable sources. This article needs additional citations for verification.
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