Ugly compression/leakdown numbers- what do I do?
 

Well gang- it looks like its time to tear into my 85 3.2. 112,000 mi, uses 1 qt-250 miles between outright burning and a rear main seal leak. I have been chasing a miss/rough idle for a while and decided to get serious this afternoon. Performed a leakdown test as follows:

Luke warm engine, loosened plugs, ran for about 30 sec and removed. Leakdown and compression as follows:

1. 4%, 140psi
2. 4%, 140psi
3. 6%, 145psi
4. 40% 120psi
5. 10% 120psi
6. 40% 120psi

Looked ugly. Put new plugs in, drove until warmed up (oil cooler thermostat was open)

Looked at #4 and #6 again.

#4 remained the same- 40%, 120psi.
#6 got better- 12%, 140psi.

Removed leakdown tester, ran 50psi shop air into the adapter for the tester, inserted plugs into the two cylinders that had air pressure coming out. Leak is to the exhaust.

After the test run (10 miles or so) plugs 1,2,3,4,6 looked normal. Number 5 was already black with soot. I believe this to be from the DME compensating due to the dead #4.

Do you think top end will cure my mess or am I in complete deep *****?

Thanks for looking!

Dave

3.2 heads are famous for wiped out valve seats. the guide gets worn, the valve wobbles around and beats the hell out of the seat. the seat is no longer round and that's why your readings are high. some of the 3.2 heads i've done are on their last valve grind, (probably just the first one for most of these) due to not enough seat remaining after they clean up. the stone assembly rides on a pilot in the new guide bore. a quick (2 seconds) buzz on the stone usually shows about 1/3 to 1/2 of the seat showing contact with the stone. shows you how much they are out of wack.

A top end should be all you need at your milage but you need to evaluate the engine yourself. Is the oil pressure good? How dirty does the inside of the case look when you remove the cylinders? etc. You need to also plan to replace the lower row of headstuds as they will probably break sooner or later.

-Andy

John, Eagle thanks for the replies. I guess the only remaining question is the low compression numbers all around. Will squirting a little oil in the cylinders to test the rings work in a 911 engine? It seems the oil may just sink to the lowest point and not affect sealing ver much to do another compression test.

Thanks

Dave

cranking speed, the gauge itself and rings not oiled up all affect compression readings. a hot engine with well oiled rings is the best time to do the test.