Compression Test Mystery

JIMS88

MEMBER
1989 VOLVO 240
100,000 MILES

Here is a problem I don't understand. My 4 cylinder volvo penta AQ151C engine quit running the other day. (It's the same basic engine that was used in countless Older Volvo Cars over many years) I thought the problem was the head so I got a rebuilt one and put it back together. It seems to be doing the same thing:
The motor won't start. I did a compression test and When I turn it over it it makes compression for about 5 or 6 revolutions, then for about another 6 revolutions it makes zero compression. This make no sense to me whatsoever but I suspect the problem is in the lower end due to the head rebuild.

Anyone have any ideas what is wrong?

Thanks,

Jim

2 Replies

ASEMASTER6371

MECHANIC
52,797 POSTS

Inject air in the cylinder to see where the leakage is coming from.

Valves seating ok?

Roy

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Tuesday, July 17th, 2012 AT 10:28 PM

CJ MEDEVAC

MECHANIC
11,004 POSTS

MAYBE I THINK INTO THINGS TOO MUCH

ARE YOU SAYING IT BUILDS COMPRESSION 1ST FEW REVOLUTIONS----THEN IT STOPS BUILDING PRESSURE (IT IS TOPPED/MAXED OUT) THE NEXT FEW REVS DOES NOT IMPROVE YOUR READING?

IN OTHER WORDS. DO YOU THINK IT IS SUPPOSED TO KEEP PUMPING UP MORE AND MORE AND MORE ON EACH REVOLUTION?

I DID READ THE QUESTION SEVERAL TIMES.I'M NOT QUITE "RAINMAN" MATERIAL YET!

THE MEDIC