Gives you a warm fuzzy feeling regarding the accuracy of this puppy. NOTICE how the tester never actually reads 100% leakage even when the leakage is at 100% through the blow tip. I connect a blow tip to the tester and set the adjustable dial so the first gauge reads 100psi.ĭepress blow tip for a second, readjust until the gauges always return to 100 after the little shots of air. I don't care if it is TDC compression or TDC exhaust. You DO NOT have to look at cam timing at all at this point. Use the timing mark on the balancer and set it to zero. How to easily find TDC and then find TDC for the other cylinders.Ĭold engine, Take all of the plugs out. You can watch the leakage "rate" increase as the feed pressure drops below 110 psi on the gauge on your compressor.Ī leak down tester will give erroneous readings if the feed pressure to it is too low I believe the leak down tester needs feed pressure at least 20% over 100 psi. If you have a standard single stage compressor they commonly cycle on at 90 and off at 125-150 psi. The tester works by applying 100 psi to the cylinder being tested. If you have a 2 stage compressor you can disregard the following: One important thing missing from most "how to" posts is feed pressure to the tester and constant re-zeroing of the tester because of the feed pressure is constantly changing. On Miatas the chamber size is approx 450cc and normal automotive testers work fine. ![]() The size of this restriction is directly related to the size of the cylinder being tested.Ī leak down tester sized for automotive engines (usually 600-700 cc cylinders) will NOT work properly for a much larger or much smaller cylinder sizes. The tester is simply two pressure gauges with a very specific restrictor between them. It is normally done at TDC (top dead center) on the compression stroke but as you will see it can be done at other crankshaft positions. ![]() This is simply pressurizing a cylinder to check both the amount of leakage and where it is leaking from. Here's my take on one of the most mis-understood engine health checks.
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