compression v. leakdown?

[Arkman]

I'm in the process of purchasing my 2nd 911. This one is an '87 Targa, triple black. Seems to be mostly original. I've been reading this board for years and I know many of you will disapprove, but I'm buying this car sight unseen off eBay. I won the bid at the $15K reserve. It seemed to be a fair price for an ’87 with 91K miles. The current owner (a professional restorer of 356’s and TR6’s) is holding about $10K in recent receipts (last 5K miles) including a top end rebuild.

I bought it contingent on a PPI and I when I asked the seller if he would recommend a mechanic, he offered to do the compression test and leak down. I took him up on the offer.

I spoke with him today and compression sounds great – 125 across all 6. He said that his leak down machine was leaking itself so he wasn’t sure of the reading…but he was getting 30%...

Otherwise this seems like a really straight deal. Professional, answering every question, said he just had his guys go through the car and replace a couple of burnt out light bulbs, had the car on the lift and pulled the tires, cleaned calipers, etc…not pushing for payment, working with me over the mail and with DMV (I’m about 2.5 hours away and would like to only make one trip).

My question to the collective wisdom of the Pelicans is should the solid compression be an indicator to rely on, or should I insist on the leak down?

Thanks in advance!

[ljowdy]

Compression can be manipulated via oil. If the rings are bad and you squirt oil into the cylinders, that will temporarily seal up the rings and you'll get a decent compression reading.

A leak down test is unique. Once the cylinder is pumped up and if you can hear leaks through the intake, then you have a burned intake valve, if you hear air leaking through the exhaust you have a burned exhaust valve and if you hear air leaking through the case then you have bad rings or broken head studs???.

In my opinion, both tests are needed. Of course, the big problem is the seller is doing the test and if he's dishonest, he can tell you anything and unless you take it to another mechanic, that's all the information you have.

[ossiblue]

Any other indicators such as oil smoke or excessive consumption? Naturally, without the leakdown it is a gamble so you have to go by your instincts regarding the seller and it sounds like you are comfortable. He does have receipts for work done that should preclude problems indicated by poor leakdown numbers, so--if you believe him and the paperwork is in order--most likely the numbers are results of a poor test. I am certainly no expert, but most who know about these things will say one test does not make bona fide results. Personally, if I felt about the seller and documentation as you have described, I'd take the risk.

[Porsche-O-Phile]

It's an old 911. Assume it will need an engine rebuild during the time you own it and you won't be disappointed.

[Arkman]

Thanks...gut feels good on this one...brain says I'm an idiot for spending that kind of money sight unseen.

[rsrfan]

Compression should be more than 126. I get that on my 930 and the pistons are at 6:5:1...

[cashman]

I have a 1989 3.2 with 45,000 mi. I agreed to buy mine on a post ebay sale sight unseen pending the PPI results. I had a PPI done by a Porsche dealer in NY and here were the results for comparison.

Compression 160-165
Leakdown 2%

Hope this helps. Good luck.
Mark

[Paulporsche]

The technical aspects aside, are you able to verify the seller's claims? You know, anyone can "publish" a test result, claim his guys did some work, etc, including claiming title.

Perhaps if you post where this thing is located, a nearby Pelican can have a look for you.

There have been lots of stories about car and parts scams perpetrated over the Internet.

Not pointing fingers. Just trying to suggest how you might feel more at ease.

[JFairman]

I have an '87 930 with stock 7:1 compression ratio and I get 120-125 psi on a compression test. A 3.2 Carrera should be alot higher.

30% leakdown is alot. I think you will have to take it to someone else for a good leakdown test or do it yourself. You need a good leakdown tester that allows you to pressurize the cylinders with 100psi air or else the rings may not be seated fully and will leak.
An example of a bad leakdown tester is a harbor freight one that only allows you to pressurize the cylinders to around 15psi - unless you replace the right hand 15psi leakdown gauge with a 100psi gauge. The left gauge shows how much air you are putting in via the regulator adjustment on the unit.
Thats the very short version on that..

While the cylinder is at TDC and you have 125 psi air pressure going into the spark plug hole, take the cap off the oil tank and insert a piece of hose and listen in the other end for hissing of air. That would indicate rings leaking.

Then listen in the throttle body while holding it wide open. That would indicate intake valves leaking.

Lastly stick the hose in the exhaust pipe or even better remove the oxygen sensor and insert the hose there. Air hissing there would indicate exhaust valves leaking.

Good luck with it.
Just because someone says the top end was done doesn't mean it actually was, or that it was done right.

[BK911]

Originally Posted by cashman

I have a 1989 3.2 with 45,000 mi. I agreed to buy mine on a post ebay sale sight unseen pending the PPI results. I had a PPI done by a Porsche dealer in NY and here were the results for comparison.

Compression 160-165
Leakdown 2%

Hope this helps. Good luck.
Mark

These are really good numbers. IMHO 125psi compression is pretty low, but at least they are consistant. 30% leakdown is a deal breaker and engine rebuild time.

[2.70Racer]

Arkman,

After being high bidder and "winning" the auction, you agreed to having the seller to perform a compression test.
He has reported the results to you as 125 across the engine.
Since you agreed to have the seller perform the test for you, which he hs done, What's the problem?
A leakdown test is called for to identify any problem found with a compression test.
If you are not comfortable with the numbers reported, discuss this with the seller. 125 is on the low side.
Remember, you agreed to the seller performing the test.
If you want out, call the seller and say so.
Don't be a weasel and ask the seller to continue to perform additional tests.
Either follow through with the agreement or bail.
The price is a fair price. Go see the car and discuss any issues man to man.

[runfaster]

I don't know what is up with that last comment, but I would have him get some proper numbers on the leak down before you went ahead with the deal. Leak downs are kind of tricky for the novice. Those compression numbers are low, they should be 160 and above.

At 15 grand you are not going to get hurt too bad... a top end is going to cost you $5000, so you now have $20000 into a solid driver. They are all 20 thousand dollar cars anyway-so you are even, point blank.

But, for the love of doomsday and dragons;do whatever you think you need to do to get piece of mind out of this deal.

He has the car, but you have the money.

Later,
Willy Wonka

[dshepp806]

get a leakdown done,..period...and NOT by the seller.

Doyle

[imcarthur]

Originally Posted by dshepp806

get a leakdown done,..period...and NOT by the seller.

Agreed.

Here were my numbers as tested by an independent during the PPI on my car:

cyl 1 182 / 5% cyl 2 179 / 3% cyl 3 179 / 2% cyl 4 180 / 2% cyl 5 180 / 5% cyl 6 180 / 5%

Ian

[Arkman]

This advice is exactly what's going through my head…
Compression is a bit low, but consistent. (So the seller says.)
It’s an 87 (with G50 as I understand ALL 1987s originally had G50s) for $15K…even if I have to put $10 into this car I will probably get it out of it…eventually…but it’s still $15K and there are lots of cars out there.
I’m an idiot for not getting a proper PPI done by a 3rd party…but the seller is a professional restorer of 356’s…I can’t see someone risking their reputation on this deal.
I don’t like the combination of the low compression and the high leakdown, but he admitted the gauge was broken…if he was really trying to rip me off, wouldn’t he just have lied?
I asked on the marketplace board if anyone knows of a good mechanic for a PPI in North Jersey – Newark/South Amboy area…I just got a response this morning…I’ll comb through that list.
Thanks for the reference #’s – those are very helpful.
And FWIW – I’m not trying to weasel out of this deal. I asked for a PPI reco, he said he would do a compression and leakdown himself if I was ok with that. I was and still am, except that he couldn’t do the leakdown properly due to an equipment issue, so I may exercise my right to take that to a 3rd party.
If there are any Pelicans in the area – S. Amboy - please PM me if you would be willing to do a drive by and look at the car…at a minimum, it sounds like he has a bunch of 356’s around to drool over.

[Nine9six]

Originally Posted by imcarthur

Agreed.

Here were my numbers as tested by an independent during the PPI on my car:

cyl 1 182 / 5% cyl 2 179 / 3% cyl 3 179 / 2% cyl 4 180 / 2% cyl 5 180 / 5% cyl 6 180 / 5%

Ian

Above is the type of test results you are looking for. Both compression and leakdown numbers on each cylinder. Not this:

Compression 160-165
Leakdown 2%

[JFairman]

A leakdown tester is such a simple device that if a gauge is tweaked or leaking, or a hose is leaking, it is easy to fix.

Air comes in from a 100-120 psi compressor or tank and goes through the built in adjustable air pressure regulator which is usually all the way over on the left side of the tool next to the air inlet.

The left side gauge displays the pressure you have set the regulator to, and that would usually be 100psi.

Then the air travels through a very small orifice in the body of the tool where it comes to a chamber under the right hand gauge or leakdown gauge.
From there the air pressure the right hand gauge is seeing goes through a hose with 14mm threads with an o-ring on the shoulder of the threads that you hand tighten into the spark plug hole of the cylinder you want to test.
The piston in that cylinder should be at TDC on the compression stroke.

If during the test that cylinder is leaking air somewhere faster than the incoming air from the compressor can go through the small orifice between the left and right gauges on the body of the tool, the pressure loss will show on the right hand gauge.
The right hand gauge is calibrated in percentage and it has to be at zero before the test (this is what the built in regulator is for) or if it it a 100psi gauge showing 100psi, then each pound displayed below 100 psi will be a 1 pound loss or 1% leakage.
Anotherwords if the right hand gauge is calibrated at 0-100psi and was zero'd at 100psi and then displaying 95psi while testing the cylinder, that would be 5% leakdown.

hope that sorta helps

[madmmac]

For $15k I would drive 2.5 hours and check it out for myself.

What are you waiting for?

[Arkman]

legit question...but I'm not a mechanic and couldn't verify anything anyway. I don't have the leakdown machine although Jfairman's description is helpful and it's 2.5 hours each direction so at least a half day away from work.

I'm going to call on Monday and ask for a proper leakdown. If its an easy thing to fix it shouldn't be a big deal...

if it were really leaking anywhere near 30%, would it be spraying oil? Engine compartment is clean (again, pictures only) and seller claims that it doesn't leak...more than a couple of drops.

Are there any other questions I should be asking that would be an indicator in either direction?

[craigyirush]

Originally Posted by Nine9six

Above is the type of test results you are looking for. Both compression and leakdown numbers on each cylinder. Not this:

Compression 160-165
Leakdown 2%

What's wrong with 160-165 and 2%?

The original poster said it was in the 120s with 30% (which I agree are not great numbers).