HeroOfSpielburg

Hi guys,

I'm trying to wrap my head around all that's needed to make a well-informed buying decision. Car is a '92 968 hard top.

In the PPI yesterday I believe I was told the compression readings came back 14:14:14:12 (I wasn't conversing in my native language so not 100% sure).

Is this a red flag that I'm going to need a valve rework or a ring job in the near future, or likely going to be okay?

Thanks for the feedback guys and helping this rookie.

D.

cruise98

What unit of measure is that ?

Paulyy

probably means
140
140
140
120
but who knows.

Jfrahm

Probably Bar, I would not worry too much if it's a street car. The numbers are not good (over 10%) but if the car has a lot of KM I would not worry about it. If it was supposed to be like new or recently overhauled I'd make it an issue. You could do a leakdown test too I suppose and re-do the compression test on a warm engine.

IMO the higher the compression the more likely you are to have diverging numbers in a compression test so the 10% rule-of-thumb is perhaps too strict for the 968.

HeroOfSpielburg

Thanks for the feedback guys. I think the mechanic meant bars, but I'll double check. I'll get a written report back early next week and revisit it. The car has only 60k miles but the first three years before it came into the country it has no service history. The manual looks also like pages may have been added (holes around the staples are a little bigger on the bottom than top), but there is a sizeable stack of receipts and government inspection reports in the maintenance binder. Hopefully there's no skeletons in the closet because I really like her.

MB968

I agree, at about 15%, that seems way too much. Indicates that you'd need to plan some work, likely on the heads. I'd think the cylinder walls would have to be pretty bad to create this much difference (and you'd see that in oil usage)

michaelmount123

The OP is getting misinformation here and it could lead him to make the wrong decisions! Mr. HeroOfSpeilburg, please consider the following:

1. Do not worry. You have not presented the correct test results, so the responses are not valid. Do check back with your technician.
2. Understand the difference between a compression test and a leak-down test. Then understand the correct way to do both tests, and what the results mean. Goggle is our friend.
3. At this point there is NO indication you have a problem.

HeroOfSpielburg

Ok, so I got the report back from the mechanic and he said the reading on the last cylinder is off by two kilobars (14 vs. 12). This is 14%. However, I called the mechanic today to clarify and he said that the car ran well idling and driving (they drove it), and it didn't seem that there were any other problems so he didn't think it was cause for concern now and the car was okay to buy. Am I making a mistake buying the car without redoing the compression test and an accompanying leakdown?

Jfrahm

Again I think it's fine for a street car and not recently overhauled. If the test was re-done following a spirited drive and a leakdown were performed you might find no issue. If it was a race car or the seller was touting a full top end rebuild that'd be different.

FRporscheman

To put your mind at ease, you should have a leakdown test done. That will determine where the loss of compression is occuring. Your mechanic should know how to determine this.

Doing both tests on a warm engine would give more information.

Van

If the test is in bar (not kilo bar), the numbers would be 203 psi and 174 psi.