Help with leakdown and compression #'s
 

I was looking at an '88 911 today with 81,000.

All cylinders except #3 came in at 165 compression and 5% leakdown. The tests were run on a hot engine.

Cylinder #3 came in at 125 comp. and 90% leakdown. Although the #3 plug looked good, the mechanic suggested running the engine for a minute in case a little carbon was under the valve. He repeated the leakdown and got 85%.

The mechanic didn't detect air from the oil tank, or breather, or exhaust. The mechanic didn't have a lift so it was never
pinpointed if it was escaping through the head gasket.

Would a bad gasket cause the numbers to be this out of whack? Would a bad valve adjustement on #3 cause this?

The owner just had the valves adjusted with his last service. He indicated he wouldn't return to that shop as they were not good. (The PPI guy noticed all the spark plugs were loose).

Yeah, it's a blown head gasket. . . on an '88 911.

Sounds like it's time to go to a different shop for your PPI.

Was the PPI done in MD? If so, curious what shop it was.

Yes, I agree there is possibly an issue with that cylinder. I wouldn’t dismiss anything until I had done some spirited driving and re-testing.

Can you hear any leak at the head under power?

Best,
Grady

3.2 Carrera engines don't use any gasket between cylinder and head! If there is a leak there ... it is because of a broken Dilivar head stud! Did the 'mechanic' check for broken head studs, or even mention the subject???

<b>Definitely time to find a different shop!!!</b> Or, start doing your own work ...

Those compression numbers on the five 'presumably good' cylinders are very low for a 9.5:1 compression engine ... by at least 15 psi!

Suppose you had five engines in your garage:

1. A 1966 2.0;
2. An 1988 3.2;
3. An 1976 930;
4. A 1991 C2 that had suffered from cylinder leakage and been repaired as part of the factory recall; and
5. A 935.

How many head gaskets would you have?

Plymouthcolt never stated that his PPI guy ever used the words "head gasket." He didn't even infer that. The way you two of you guys are treating him, I wouldn't blame him if he went and got a new BBS.

I was not aware of the lack of gaskets, this would be my first 911 and I am still learning.

As far as the compression numbers, that's what appeared on the dial. My eyes saw 165 and that's what the mechanic read aloud. Either the engine has major issues or the compression tester was faulty.

The PPI guy said it was either a broken stud or it could be carbon build up on the vaalve as the car is driven maybe once a month.

$3K or $4k? to fix is not in my budget, and I can't take that chance so I passed on this one.

Grady-he couldn't hear any leak under power.

Thanks Zeke.

Uhh, thanks for coming to our new member's defense, Zeke, however, the original point that I was trying to make is a simple one: A mechanic who does not know that the only 911's to use head gaskets were the repaired C2s and certain turbocharged cars should NOT be the one selected for the PPI.

If his client comes away from the inspection thinking that the car has a leaking head gasket, the mechanic either lacks the requisite knowledge or failed to explain to his client what the problem is. Either way, he's setting up our friend from Maryland for a potentially expensive and unpleasant 911 ownership experience, which nobody here wants.

Please consider my style for the spirit in which it was intended, which was to warn our new friend, not to make fun. There are folks on this board who have forgotten more than I'll ever know about the 911 and you don't see them hassling the new guys, nor was I.

Can I recommend, if you haven't already read it, a copy of 101 Projects for your Porsche 911, written by and available from our host Wayne Dempsey? It is probably the best single volume ever written about Porsche cars. Armed with it and the collective knowledge of this board, you can find yourself the right car and be confident in your decision.

I'd only add to JohnC's post that you might also want to pick up a copy of "How to Rebuild Your 911 Engine." Not that you will, but it does cover when and why you should rebuild. Good reading to determine years of engines and their specific problems/strengths.

John

Actually I just got the book and I'm going through the engine section-I love this book.

I am so confused. I checked with a local Porsche "guru" here in Maryland and he said I should have bought the car. He says "carreras do not break head studs--it was most certainly carbon buildup".

So I don't know if I passed up a great car with a correctable problem or a money pit.

oh well, I'll just keep looking.

Nothing wrong with passing if you are not sure. Many guys look for six months to find the right car.

I did a leakdown test on the engine of my race car and came up with 80% leakdown on cylinder #4. Initially, I was concerned that I had over-revved the engine and bent a valve. So following the advice of others here, I took the car for a high-speed test drive which included a few miles of highway driving at wide-open throttle. After that, I poured some B-12 chemtool down the #4 intake stack and revved the engine in an attempt to blow out the carbon. Other guys have had luck pouring water down the intake, check the archives for this procedure.

I repeated the leakdown test and it showed 5%, no problem.

So it's entirely possible that the car you looked at was problem-free. Then again, it's entirely possible that a complete top overhaul was warranted. The next step would have been to look inside the affected cylinder with a borescope to see if a valve had burned.

Well, you sound like you are on the right track: educate yourself as fully as possible and don't hesitate to post details of potential new acquisitions here: these guys can point out trouble spots just from looking at the pictures. Good luck!

I walked away from 2 cars - 85 in Houston & 88 in Pensacola that failed compression & leakdown with similar figures.

You made the right choice.

If you already own the car, then John's 'blowout' solution makes sense. But if you're just shopping, it is not worth the risk. Walk & keep looking.

The one I bought had <5% & 180 +/- 2 on all cylinders. They are out there.

Ian

So would 6% leakdown on 1-4 and 6, and 5% on 5 be decent? Does having the numbers consistant across the board matter?