Compression numbers on '82 SC, etc.

[Looking_for_911]

I've been looking at an '82 SC coupe that is out of state. I had the owner take it to a recommended shop for a PPI. They returned a report with compression numbers of 100, 120, 120, 120, 110, 120 on an engine with 172k miles. A leak down of 4-percent was reported on the #1 cylinder with 100lb compression.
A valve job was said to have been done on the car by the previous owner.
It uses no excess oil, doesn't smoke, even on cold start, and runs like the proverbial top. The owner doesn't have to sell it, doesn't need the money, is not pushing it, so I believe him when he reports the car runs good and sound.

The car has some cosmetic issues like a rusted rear bumper support, and a few other things that are not too bad - save a cracked windshield that apparently happened while in the shop yesterday.

With the consistency in the compression numbers - albeit they seem a bit low to me - could such an engine be expected to last much longer before needing the bottom end rebuilt? And what how much you fellow Pelicans feel comfortable in putting into such a vehicle.

Thanks!

[Peter Zimmermann]

Something is weird here. Get a full leak down test done, and forget the compression numbers...

Here's a little reading material for you:

http://forums.rennlist.com/rennforums/911-forum/189606-the-pre-purchase-inspection-by-peter-zimmermann.html

[Looking_for_911]

Thanks Peter....
Anyone know of a good, reliable Porsche shop - one that knows How to do a proper PPI - in or near Yorktown, Virginia? I'd appreciate suggestions!

[2.70Racer]

Pete Z is correct.
A low compression and a normal leakdown number are at odds with each other.
The numbers reported to you are not correct.
The compression numbers are inline with a 175K, 27 year old car.
A compression test and leakdown, check the condition of the cylinders, pistons, valves and seal of the heads. A top end job, rings, valves, and studs would improve low numbers.
Until a proper compression test is run, you really don't have reliable information as to the condition of the above mentioned items.
A compression and L/D test do not report the condition of the bottom end.
Low oil pressure is a first indication of bottom end condition.
Remember it's a 27 year old car, If all else is ok and you keep back $3,000 for repairs, it may work out.
How is the trans? Does it shift with no issues?
Has the clutch been replaced recently? Within the last 5 years, 50K miles?
Clutch and trans work can easily run $3,000.
Alternator, starter, fuel pump, plugs, wires, rotor etc can add up.
Brakes and tires too.
For me personally, an SC with 175K in good shape with records is worth from a low of 7K to as much as 15K for a prime example.
The 20K rule is in effect for this type car.

[Looking_for_911]

Hey Doug,

Thanks for the great info...

Even being a newbie to the 911 world I thought a "normal" leakdown number on a low compression cylinder sounded strange. I suspect they didn't perform the test correctly as their work seems to be somewhat suspect in other areas. We used them because they came recommended by a PCA member and the car owner had service done there in the past. He is livid over the ordeal as am I. Looking back I should have eaten the cost of the PPI (it took them two trips to do the leak down) and had him take the car to another shop for a correct series of test. (I'm three states away, that's why I didn't do this myself)

To answer some of your questions. Owner reports the car shifts as it should, clutch function is as it should be. The alternator, starter, fuel pump, plugs, wires, rotor all seem to be in good shape as he reports the car starts easily; doesn't smoke, even on cold start; doesn't leak oil to any degree and runs like the proverbial top. Tires are brand new; brakes in good shape. Major issues now include a newly-cracked windshield courtesy of the shop on this PPI trip; a "rusted out" - the owner hasn't verified the condition yet - rear bumper support and the air conditioner components are in a box (which I knew about) and very nice Porsche seat covers cover worn seats. There is a very small rust discoloration (on white car) on the cowl under the cracked windshield near where the wiper arm connects.

The shop seemed to be all over a few scratches on the dash and things of very minor cosmetic nature in their report, but they have still as of yet given me a report on the road worthyness after I reminded them again that I needed to know about the suspension components.

Maybe the shop did their best, I don't know. It's that thought that keeps me from really pitching a fit, as Grandmother would have said.

If anyone else would weigh in on this issue it would be greatly appreciated.

[craigyirush]

I'd ask him what the average oil consumption is.
And you can do the decel test (see Pete's book) to see
if the guides need replacing.

[bkreigsr]

these guys helped us buy a 135,000 mile 81 targa, 351 miles from home, by doing a leak down test.
very knowledgeable and friendly, ask for Robert Overholser, owner/founder
http://www.lufteknic.com/
worth the trip from Yorktown.
Bill K

[Looking_for_911]

Thank you to those that have taken the time to write replies and PM's. I appreciate it.
Every 911 owner had to go through buying the first one, and your advise is making the process less painful.
--Jeff

[T77911S]

Originally Posted by Peter Zimmermann

Something is weird here. Get a full leak down test done, and forget the compression numbers...

Here's a little reading material for you:

http://forums.rennlist.com/rennforums/911-forum/189606-the-pre-purchase-inspection-by-peter-zimmermann.html

if you are saying to do a leak down only, i do not agree. i do agree that the nimbers posted are of no value, if they are acurate, the rings/valves are very bad and the leak down was bad(wrong). you need to get BOTH leak down and compression done. either way, count on a rebuild for that one.

i just did a compression check on my mazda 2200 with 170k miles, all 4 were at 145 psi. one did hit 150 once. i think my 2.7 was in the 150 range also, been a while.