993 compression test results/question
04-19-2012, 09:26 PM
#1
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993 compression test results/question
Had a PPI done on a 98 993 with 45k miles that has been only driven 100 miles in the last 2 years. Results are as follows:
1-180
2-185
3- 95
4-190
5-195
6-190
My question is this. Does the one cylinder at 95 necessitate a top end job? The mechanic who did the PPI said, "leave it with me and $10k and it'll be good as new". I've talked to two other mechanics who say 993's have carbon build up issues, especially if sitting for long periods and suggested driving it for 1000 miles or so to see if it clears up. I have not bought it yet so am looking for advice. Thanks in advance!
1-180
2-185
3- 95
4-190
5-195
6-190
My question is this. Does the one cylinder at 95 necessitate a top end job? The mechanic who did the PPI said, "leave it with me and $10k and it'll be good as new". I've talked to two other mechanics who say 993's have carbon build up issues, especially if sitting for long periods and suggested driving it for 1000 miles or so to see if it clears up. I have not bought it yet so am looking for advice. Thanks in advance!
04-19-2012, 11:49 PM
#2
Drifting
I'd get the seller to drive it a 1000 miles and see if it clears up 
Seriously, I would walk away unless that problem is resolved. A leak down test would tell you more about where the loss is coming from. It could be rings or valves. I had a leak down test when I bought my car and the mechanic who was very experienced in Porsche engines, said the leak down numbers on one cylinder (6%) would likely get better after a few hard miles. The car had not been driven much for 8 years. I never did get it retested so who knows.
Seriously, I would walk away unless that problem is resolved. A leak down test would tell you more about where the loss is coming from. It could be rings or valves. I had a leak down test when I bought my car and the mechanic who was very experienced in Porsche engines, said the leak down numbers on one cylinder (6%) would likely get better after a few hard miles. The car had not been driven much for 8 years. I never did get it retested so who knows.
04-19-2012, 11:51 PM
#3
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I'd get the seller to drive it a 1000 miles and see if it clears up Seriously, I would walk away unless that problem is resolved. A leak down test would tell you more about where the loss is coming from. It could be rings or valves. I had a leak down test when I bought my car and the mechanic who was very experienced in Porsche engines, said the leak down numbers on one cylinder (6%) would likely get better after a few hard miles. The car had not been driven much for 8 years. I never did get it retested so who knows.
Seriously, I would walk away unless that problem is resolved. A leak down test would tell you more about where the loss is coming from. It could be rings or valves. I had a leak down test when I bought my car and the mechanic who was very experienced in Porsche engines, said the leak down numbers on one cylinder (6%) would likely get better after a few hard miles. The car had not been driven much for 8 years. I never did get it retested so who knows.
04-20-2012, 12:01 AM
#4
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*I* have never seen an engine with low compression magically get better without fixing something broken inside. Whether a valve or a compression ring, unless it's cheap enough to warrant you repairing it properly, why bother.
04-20-2012, 01:14 AM
#6
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04-20-2012, 05:41 AM
#7
Pro
Hi There
I had the same thing on my car. It drove perfectly though. For me it was a broken piston ring, but I would try a can of BG44K in the gas tank and also squirt some redex or similar into the offending cylinder. It could be a stuck ring.
If the car is otherwise great then price in a strip down to fix the ring or valve. The engine does not need a rebuild at those miles so it should cost nothing like the figure you have been quoted. Only half the top needs to come apart really.
All the best
Berni
I had the same thing on my car. It drove perfectly though. For me it was a broken piston ring, but I would try a can of BG44K in the gas tank and also squirt some redex or similar into the offending cylinder. It could be a stuck ring.
If the car is otherwise great then price in a strip down to fix the ring or valve. The engine does not need a rebuild at those miles so it should cost nothing like the figure you have been quoted. Only half the top needs to come apart really.
All the best
Berni
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04-20-2012, 10:58 AM
#8
Drifting
04-20-2012, 04:26 PM
#9
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Hi There
I had the same thing on my car. It drove perfectly though. For me it was a broken piston ring, but I would try a can of BG44K in the gas tank and also squirt some redex or similar into the offending cylinder. It could be a stuck ring.
If the car is otherwise great then price in a strip down to fix the ring or valve. The engine does not need a rebuild at those miles so it should cost nothing like the figure you have been quoted. Only half the top needs to come apart really.
All the best
Berni
I had the same thing on my car. It drove perfectly though. For me it was a broken piston ring, but I would try a can of BG44K in the gas tank and also squirt some redex or similar into the offending cylinder. It could be a stuck ring.
If the car is otherwise great then price in a strip down to fix the ring or valve. The engine does not need a rebuild at those miles so it should cost nothing like the figure you have been quoted. Only half the top needs to come apart really.
All the best
Berni
04-20-2012, 05:49 PM
#10
Seems a little fishy. How can your mechanic quote you $10K when he doesn't even know what's wrong with the engine? Not very confidence-inspiring.
It's also extremely unusual that a 45K motor would have a major internal problem. I would take the car on a spirited drive and then re-do the compression test at another shop. Won't cost you much, especially if you have the shop only test cylinder #3. Given the stakes here, and given how easy it is to do a second test, before proceeding IMHO you should double-check whether the original diagnosis was correct.
It's also extremely unusual that a 45K motor would have a major internal problem. I would take the car on a spirited drive and then re-do the compression test at another shop. Won't cost you much, especially if you have the shop only test cylinder #3. Given the stakes here, and given how easy it is to do a second test, before proceeding IMHO you should double-check whether the original diagnosis was correct.
04-21-2012, 10:08 AM
#11
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Seems a little fishy. How can your mechanic quote you $10K when he doesn't even know what's wrong with the engine? Not very confidence-inspiring.
It's also extremely unusual that a 45K motor would have a major internal problem. I would take the car on a spirited drive and then re-do the compression test at another shop. Won't cost you much, especially if you have the shop only test cylinder #3. Given the stakes here, and given how easy it is to do a second test, before proceeding IMHO you should double-check whether the original diagnosis was correct.
It's also extremely unusual that a 45K motor would have a major internal problem. I would take the car on a spirited drive and then re-do the compression test at another shop. Won't cost you much, especially if you have the shop only test cylinder #3. Given the stakes here, and given how easy it is to do a second test, before proceeding IMHO you should double-check whether the original diagnosis was correct.
04-21-2012, 05:22 PM
#12
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If it is a stuck ring try BG 109 . Put it in your engine oil once it is up to temperature and let it idle with some short slight inreases up to 2000 rpm from time to time. 10-15 minuites. Do not overfill so if its right to the top you might have to drain some oil out to get the 10 ounce can in. Drain the oil after and refill with fresh oil. If it is a deposit stuck ring of any kind it will free it up. Its perfectly safe when used properly.This is more frequently seen on the new DI engines but it can happen and worth the cost of the kit.
04-21-2012, 10:16 PM
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I would ask the person that did the leakdown if they could determine where the air leak is coming from. I am not familiar with the leakdown done on Porsches. But being an aircraft mechanic and working on aircraft engines of similar design (horizontally opposed air cooled) we use the differential compression method which allows you to detect/ hear where the air leak is. It could be from the intake or exhaust valve seats. Very common to have some carbon buildup on the exhaust valve seat and leaking air in the exhaust manifold for that cylinder. Staking the rocket arm/ valve stem against the spring can dislodge the carbon and reseat the valve.
04-21-2012, 11:33 PM
#14
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If you like the car you might consider approaching the seller with your mechanics repair quote, and use that as a leveraging tool to see if he will drop the price 10K.
Then fix it from there.
Then fix it from there.
