300D Very Low Compression
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1976 Mercedes 300D
300D Very Low Compression
Okay this is my first car and I am slightly frustrated with her. I own a 1976 Mercedes 300D with the W115 chassis and OM 617.910 engine. We bought it with a blown head gasket. I replaced the gasket and now I am still having issues. I fear injector timing could be slightly off because I reset it to TDC on the crank and lined up the marks on the cam but there is also a gear that controls the injection timing right? Also, out of curiosity I just checked the compression and got a reading of about 75 PSI, extremely low. I am fairly sure the valves should be closed because the timing is correct. Any help is welcomed.
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Joined: Jan 2010
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1997 E300D
In this situation a compression test says something is wrong, but a leak down test can be used to determine where the air is leaking to. The general principle is to pressurize the cylinder at TDC on the compression stroke, and listen for the air leak. If it is into the crankcase you have a ring problem. If you hear it in the intake it is an intake valve problem. If you hear it in the exhaust it is an exhaust valve problem. If it is leaking into the engine bay it is a head gasket. Any good mechanic can do this test for you.
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