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| 1800vw
Leakdown Tester
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Leak down testers have been used by the aircraft industry for
years. The compression tester had it's place, but that was 20 years
ago. It told you the peak pressure generated in the combustion chamber on
the compression stroke. These reading are unreliable, as they depend on
cranking speed. If the cranking speed is not exactly the same, then the
reading are off. A fresh engine is tight and hard to turn over. The worn
out motor with loose mains & rods will spin faster. Have some valves
leaking on one of the cylinders not being checked and the
motor spins faster. The other thing with the compression tester is you
will have no idea why the reading is low.So how do you evaluate the motors physical condition after you pitched the old compression tester. Buy or build a leak down tester. The one above we made from an old regulator from a gas welder, one extra gage, short length of hose, two air chuck connectors, one old broken spark plug and an internal plug with a .060" hole drilled in it. Now you can buy one that's much prettier or make one with a cheap regulator ( ) but being thrifty, I use what I have laying around. First will explain on how to use the leak down tester and later we will explain how to make one. First thing you need is a supply of air, 100 lbs pressure or more. With the Piston at Top Dead Center and both valves closed, screw the spark plug connector into the spark plug hole and your ready to began. Adjust the air pressure to read 100 lbs on regulators gage. Now with the restrictor Plug (the one with the .060" hole in it) in the regulator outlet just before the second air gage we can read the second gage to see how well the cylinder is holding the 100 lbs pressure. If every thing is sealed 100% the second gage will read 100 lbs. In practice, there will always be some leakage past the rings. When checking a motor in perfect condition with the rings seated in you will loose about 3 to 4 lbs of pressure. The great thing about the leak down test is you can tell where the leakage is coming from. All you have to do is listen at the carburetor, exhaust and the crankcase vent. A leaking valve or a scored cylinder will be very easy to detect. If you don't have an old pressure regulator laying around you can purchase one at most hardware stores, or any place selling welding supplies. How to Check Lower end-> ck How to check if P&C need replacing-> ck Go Back
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