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Engine Rebuild (low compression)

Old 07-04-2019, 07:06 PM
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G35 manual coupe
Angry Engine Rebuild (low compression)

So a few days ago I bought an 03 manual coupe with and engine that would crank but wouldn't start. Before I bought it I did a compression test only on the driver side 3 cylinders and got 30-40 psi in each cylinder. I brought the car back and started on an engine rebuild thinking it would be a head gasket issue. My coolant had a lot of chips of RTV and metal shavings in it, and once I pulled the heads off the head gasket looked perfect. The cylinder walls seem to be in good shape giving me no indication of bad rings. (however the car does have 190k on it) Valves also seem to be ok but I'm kinda new to this so I don't really know what I'm looking for. I probably should have done a leak down test before I tore the motor apart but it's a bit late now

I also feel like my compression tester could have been bad but I don't have another car to test it with and even if compression was fine I don't really know why the car wouldn't have started. I checked and the spark plugs were getting Sparks and injectors were flowing as well.

How would I go about checking if rings or valves are bad? Or could timing be an issue?

Any help would be greatly appreciated. Thanks
Old 07-04-2019, 07:55 PM
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Valves you have to bolt the engine down to a test deck which is basically a flat plate with the proper bolt holes, then you apply air pressure through the spark plug hole and monitor it for any leakage. Usually this will be done by the shop rebuilding the heads after they're done with valves, porting, and decking them.

That's SUPER SUPER low compression, are you sure you were doing it correctly? If you were doing 7 engine rotations and it never went above 40psi on that entire bank I'm thinking it was something like the timing chain skipped a tooth.
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