Compression leak down question

[runehar]

Hi, i consider buying a 1990 911 C2. milage 116500

I asked for a compression leak down test for it, and the seller replied

"A compression leak down test was done on the car before I bought it. The results were a low of 6% and a high of 20% in one cylinder. The mechanic said that he thought that one cylinder was high because the car had not been driven much of late and that the numbers would get better if the car was used regularly (it went for several months without being driven before I bought it). I asked him what kind of life expectancy the engine had left and he said that in his professional opinion that the motor should last another 50K miles before anything major needs to be done. The car runs and drives great and I would not hesitate to drive in anywhere"

I don't know much about this, and would really appreciate an opinion from someone who knows... How bad is high 20%?
I understand that the engine will need a top end rebuild, but it would be interested get an opinion on how much longer it will last. What cost's am i looking at... (i'm thinking about doing the mechanic part of the overhaul my self)...

Thanks guys.

Rune H.

[911pcars]

Arrange for your own independent PPI. The shop can then tell you if the 20% leakage is from the top end (valves or ?) or bottom end (rings or ?). Price the vehicle accordingly based on the inspection.

If it's a long distance purchase, it's riskier, but maybe mitigated by friendly Porsche people in the area who can take a look at the vehicle and can steer you toward a good shop. You should see it in person before purchase.

There are too many stories of favorable PPIs from the seller's wrench that end up not favorable to the buyer.

Sherwood

[quint22cp]

I have an 88 3.2 and it had only done 68K when I tore it down because it was down to 20% on one cylinder it turned out to be rings.

The car started an ran perfectly but I could not live with the knowledge that it was giving less than it could. I took it to a dyno and they confirmed that it was down to 201 bhp when it should be 231 bhp.

In short if you are really concerned then get it dyno'ed.

These engines don't like short trips where they don't get warmed up, this wears out the rings prematurely and hence low compression.

Sorry for the bad news, but if you can live with a few hp down then it's OK.

[Eagledriver]

That's too much leakdown to consider "normal". You could have a valve that's leaking and will start to erode (burned valve) or you could have a broken ring. The car may run for years this way but used 911's are not rare enough to take a chance on unless you get that factored into the price.

-Andy