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Compression test, plugs in or out 700 1986

posted by  v diddy on  Sun Feb 17 07:50 CST 2002
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I have read on several posts the correct method of doing the compression test ie: remove coil wire, prop open throttle plate, remove fuel pump relay, test for four strokes, but should I leave the spark plugs in the block when turning over the engine or out?
I only ask this because my readings done with plugs removed was higher than in.

thanks in advance.

1986 740 b230ft 330k kms








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Compression test, plugs in or out 700 1986

posted by  dylant on  Sun Feb 17 08:24 CST 2002
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last visit: Tue Oct 16 15:08 CST 2001
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While I'm new at this both the Haynes manual and the instructions that came with the tester instructed to remove all spark plugs. Dunno why. Out of curiousity, what readings did you get with plugs removed vs. plugs installed?

-dylan








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Compression test, plugs in or out 700 1986

posted by  Don Foster on  Sun Feb 17 08:23 CST 2002
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last visit: Sun Oct 5 11:53 CST 2014
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"...should I leave the spark plugs in the block when turning over the engine..."

No. All plugs out.

If you find one cylinder noticeably lower than the other three, squirt some oil in that hole, crank for ~10 seconds (to distribute the oil) and re-measure the compression. If it comes up then it means the compression rings are worn. If it stays low, then it means a valve is bad -- it's usually the exhaust valve, though not always.

"...readings done with plugs removed was higher than in..."

The engine cranks faster.
--
Don Foster (near Cape Cod, MA)







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