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I just replaced the head gasket in my 1992 Civic. Started it up before putting everything back together (just a second since it had no coolant, exhaust wasn't connected, etc.) and it ran fine. But now after putting everything back together and filling the cooling system, it won't start. Turning the key, the starter motor runs, and the engine turns with virtually no resistance - so smooth that at first I thought the starter motor was just spinning without turning the engine.

What's the best way to go about diagnosing the problem? I don't see anything obviously wrong - no visible leaks, etc.

R.. GitHub STOP HELPING ICE
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The other answers and my suspicion based on them were right: the problem was lack of compression due to the timing belt having slipped. I took out the #1 spark plug and brought it to TDC, and found that the cam sprocket was off by 90 degrees from where it should be. After centering all 4 pistons to avoid interference with the valves, adjusting the cam sprocket to the "UP" position, and then moving #1 back to TDC, the engine runs again. I can't confirm yet that it's not damaged; it lacks power, but that could be from exhaust fumes in the engine compartment (2 of the studs that hold the exhaust pipe to the manifold broke taking it off) and/or old, dirty/corroded spark plugs.

R.. GitHub STOP HELPING ICE
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If it is spinning with no resistance, you don't have any compression. You should be able to test this pretty easily as you'll probably be able to spin it over quite happily with a spanner on the crank pulley. I can't see why that would suddenly happen when refilling the coolant system though, unless there was a problem with the new gasket installation.

What caused you to need to replace it in the first place? That might give some clues.

Nick C
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If the timing belt did slip due to lack of tension with accessories on it, the lack of compression may well be due to some smashed valves... I believe the Civics are all interference motors. See if you can confirm or deny that before you start pulling the head. Anyone know of an easier way to check the valves? Are there any strong indications of damage from just pulling the valve cover?

Brian Knoblauch
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