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Tech Talk Technical Discussion About The Nissan 240SX and Nissan Z Cars |
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#11 | |
GM2 (SW/AW)
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you have to understand what gives the motor compression before you can try to do all this work yourself.
seriously look over this website and school yourself, not trying to come off like a douche. How To Do A Compression Test on Car Engine Leak Down How To Do A Compression Test on Car Engine Leak Down Q. What if the compression is too low or too high? A. If the compression results are too high or too low, you might consider consulting a professional technician. Modern vehicles are complicated to test and I have witnessed disastrous outcomes when a Do-It-Yourselfer has attempted this test. If however, you are fearless in your endeavor to diagnose the problem, then use the following techniques. Consecutive low compression in all cylinders could mean that the problem of fuel washed cylinders exists. This means that the engine has had too much fuel introduced into it and all of the oil has been washed off the cylinder walls. The oil creates a sealing effect between the piston and ring assemblies and the cylinder walls of the engine block. Without this thin layer of oil, the engine compression would be allowed to escape into the crankcase. This is common with an engine that has a 'flooding' problem. If the engine seems to run normally but is weak and puffs a small amount of bluish smoke, it could be an indicator of worn piston rings and cylinder walls. In either of these events, use a small oil can and squirt a little oil into each cylinder, then repeat the compression test. If the compression dramatically increases then you have found the problem(s). If the compression readings do not change, then it would indicate a timing problem between the camshaft(s) and the crankshaft of the engine. The timing chain or belt would need to be checked for proper timing. If you find the compression reading is very low or zero in one cylinder, it is highly probable that internal engine damage exists such as: * The piston could have a broken connecting rod or a hole in it. * A valve could be stuck or leaking. * There could be a broken valve spring or a bent push rod. * The camshaft has excessive wear and is not opening the valve(s). ******* If the compression is low or zero on two adjacent cylinders, it would indicate: ******* There is a 'blown' or weak sealing surface at the head to block mounting area, which basically means a bad head gasket. ******* The camshaft is broken in an area that operates valves for two adjacent cylinders. When the compression is found to be too high in one or more cylinders, this would be an indication of excessive carbon buildup in the engine. It can only be corrected by performing a chemical de-carbonizing process on the engine or by removing the cylinder head(s) and physically removing the carbon that is attached to the cylinder portion of the head(s) and the tops of the pistons. Now that being said, get your block machined to match the head... that was your first mistake, not doing.
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