Jean

Bandits, welcome to RL and congratulations. Enjoy the car, it sounds like a great purchase.

bandits47

Thanks. I was waiting to post the results until I had the car in my garage (with the ability to take pics of necessary), but wanted to clarify a couple things since the post involved my car. Lots of great people and info here!

ScottMellor

This is my last post on the subject:
Let me analogize this to the medical community.
Let’s say a doctor makes a claim about a new treatment. How does the layperson/consumer evaluate whether or not it is accurate? The answer is a peer-reviewed analysis of the claim. It gets even more important if the doctor is marketing his services.
Peer review is the litmus test of any scientific data. Now the doctor may be absolutely 100% right, and be the best looking, kindest, smartest guy in the world. Usually the peer review will analyze what he is saying and if it is correct will endorse and support it and it then becomes mainstream. Until then, it is unknown if it is true or not. It does not mean it is right or wrong.

The layperson/consumer can only sit on the sidelines until the experts decide whether or not the claims hold water, because any opinion they may infer is fairly meaningless.

Now in this instance Kevin has stated:
1 to 2% is perfect
3 to 5% normal
6 and 7 % wear setting in
8% kiss your money in your wallet goodbye
9 and 10% worn guides, possible cylinder liner problems (A direct quote from an email Keven wrote)

Ok sounds very reasonable to we laypeople/consumers and Kevin seems to be very knowledgeable and have many happy customers on Rennlist. BUT saying something passionately again and again on a web board does not make it true.

So how does the layperson/consumer evaluate this information?
We do a quick Google. This is tough because internet experts are a dime a dozen.

Wayne Dempsey on the Pelican board writes:
A newly rebuilt engine should have leak-down percentages of around 3-5%. An engine in good running condition should show 10% or less. Numbers around 20% indicate some wear of the engine, but are still adequate for good engine operation. Leakage numbers of around 30% indicate that there are problems brewing, and that a rebuild may be necessary. Needless to say a large leakage amount like 90% indicates that there is a hole in the combustion chamber, and the engine is probably not firing on this cylinder at all.
I have no idea who Wayne Dempsey is. Hmmm seems like less is obviously better, but this information is significantly different than what Kevin has said. These cars are 10 years old, so expecting new engine numbers is obviously un-realistic.
Now what? So you ask a peer of Kevin’s (assuming Kevin has 30 years of Porsche only experience and has built tons of engines) about this new set of criteria that have been postulated.
And they reply “That does not correspond to my experience, show me where that data comes from?” and “Let me consult with some other qualified Porsche technicians.” “They do not have any data to support that claim either.”

So then you ask a representative of PCNA what they think and get the official company line from the manual.

I am trying to get Mike Schatz to join in here so that peer discussion can take place. Only the guys up to their armpits in Porsche air-cooled engines can sort this out.

Kevin

I haven't written that one has possible cylinder liner problems at 10%..

I have mentioned that the rings wear very well in these engines..

Let me quote from a guy who has a little more regard to these engines from his handbook..

Bruce Anderson > Porsche 911 Performance Handbook > page 46

"Most people will tell you that 5 to 15% leakage is okay. But most good running, well maintained Porsche engines will be less than 3 to 5%

As I have said earlier, if you are a buyer. Please consider all your options. Buying a 993TT with a leakdown between 0 and 5% will give you years of driving. Leakdown ranges between 8% and 10% point toward accelerated valve guide wear. Leakdown greater than 12% have valve guide clearance issues.

Folks if you feel the need to email me, do so. Selling a 993TT with leakdowns at 8% and greater will greatly impact your sales price..

lruss

wouldnt it be great if the average TT owner could do their own leakdown and compression tests.

Droops83

To change the subject slightly, there is a quick and easy test to see if the SAI ports are clogged in any 993, TT or not. You need the PST2 scan tool, and you need to look at a live plot of the oxygen sensor voltages on both banks on a fully warmed up engine. Then, you remove the SAI pump relay and jump it to turn the pump on. The pre-cat O2 sensor patterns, which normally look like a sine wave, should flatline near the bottom of the scale after the pump turns on, meaning that the SAI ports are clear and the O2 sensors are seeing all the extra air from the pump. If the O2 sensors don't respond at all to the extra air or the pattern is jagged or erratic, this indicates that the ports are at least partially blocked. At this point, a full checkup of the SAI system is needed (check valve, etc) but clogged ports likely point to worn valve guides if the rest of the SAI system is functional.

This test is a must on any PPI of a 993 in addition to the usual compression/leakdown tests.

lucycan

Not exactly but they MAY to some extent. Take a low mileage (10-20k) TT and don't drive it for 4-6 months. Drive it right away to have a leakdown test. Numbers could be 10%+ easily, I think. Drive it around for the next week and put, say, 250 miles on it, and I THINK you can get those numbers down.

At least thats what I have been told (in some fashion) by mechanics from coast to coast.

MarkD

You can buy a gauge set for <$100... of course, you need an aircompressor to do the leak down. The hard part is getting to the plug holes.
Kevin, regarding the valve guide wear/leakdown linkage.
I assume you are saying that if the valve seat is leaking 10%+ then it must be due to worn guides allowing the valve to seat at various angles?
Seems that there could also be other reasons for leakage in this range. I understand the bottom end on these is traditionally solid. And what about an overrev that kisses a valve?
We should be clear that the guides are the likely culprit and root cause, but not the only one.
I realize I am slitting hairs to some extent. I think your point is that it will cost you $$ with leakage at that level.

Kevin

Jason, why would you risk it when you are buying a car.. You yourself are "looking for a 993 weekend car" Would you fork out $60 to 75K for a 993TT on a buyer inspection with 10% leakdown expecting it to get better. I seen that you posted a 10K car, but most of us aren't buying 10K mile cars. I have seen a 993TT need a topend at 19K miles (guides). This was 6 years ago.

I have written, in my previous posts that if you have a 10% or lets say a 12% leakdown and here the air leaking into you exhaust system that means that your exhaust valves aren't sealing. Again you can hear it. We aren't talking about one stray cylinder with a reading off the chart that "Could" be carbon lodged between the valve and valve seat. You are looking at worn guides.. I don't care how many miles you drive the car, the valve guides aren't going to "drive" themselves healed.

Emotions take over when you have money to burn and you have found a car that you have been wanting for some time. My rant is to lay a little "caution" before dropping your cash down on a 993TT. And when you are having a PPI done, ask the mechanic for the spark plugs. In order to see the spark plugs I would order a spare set of Bosch FR6 LDC, and bring them into the mechanic. He is removing all the plugs (hopefully>>that's another story) if you buy the car you will have new plugs installed, if not, you just gave the owner a early Christmas gift.

rome

My experience supports this. I bought my car in April 2007. I was present for the PPI (done by a shop widely considered on of the best in the country), including the leakdown. I don't recall the exact figures, but I was standing there when the tech perfrmed the leakdown test and said the figures were as good as he's seen. My car had only 29,000 miles when I bought it.

I checked the oil after a few gas fillups and saw that I was burning a quart every 600-700 miles or so. I watched it closely. I even switched to a heavier weight oil.

In the end, it was clear that I was burning about a quart every 650 miles.

I went ahead with a top end rebuild a couple weeks ago. https://rennlist.com/forums/showthre...ferrerid=34752 The shop (same as did the PPI) confirmed the valve guide wear and also wear of the exhaust valves.

So, in my experience, a near perfect leakdown doesn't necessarily mean that there is not valve guide wear, and a top end may very well be in your future. Valve guide wear is a known and pervasive problem with many (most?) of 993's. But,itisworth noting that there is a legitimate debate about about when a top end is really necessary (read thread above).

Kevin

Mark, my warnings are based on valve guide wear on a 10 to 12 year turbo engine. Usually with a kissed valve the leakdown numbers are higher. We can also add a breach between the cylinder head gasket and liner. Those numbers will also be higher.

As the guides start to wear, oil passes thru between the valve stem and guide. It is burned off into the exhaust port. If you want to inspect them, you can drop the heat exchangers. A engine that has over 60K in miles I would drop the heat exchangers and look at the guides along with the ceramic liners that are in the exhaust port.

lucycan

Ive got plenty of caution left in my search.

pu911rsr

Seems to me the reasonable thing to do is to buy one with the motor already gone through. Do they last better 2nd time around.
Phil

993TurboS

So, doesn't a top end rebuild cost something like $10k? And isn't it the case that, after a top-end, you can be pretty confident that the leak downs will be <5%? So, why $45-50k for a high mile car, if what you are worried about is the leak down? If I have a 60k mile car that I have kept in as-new condidtion, but has a leak down of 12%, to me, that car is worth $60k still if I know that I can get it to <5% and get 60k more miles out of it for $10k.

Let's be real, 10k is a decent amount of change, but the variability in prices on these cars is like $45k - 95k. What is a a top end rebuild in that range? Squatola. 20% of the variability.

Perhaps there is something that I am missing, but if it is true that a top end rebuild can assure a low leak down, and it costs only 10k, then I say big deal, I am going to care more about how perfect the car looks, and pony up the 10k to fix the leak down after the fact.

MarkD

But when a leakdown test is done, the guides are not in the picture. The valves themselves, valve seats, piston rings and seal at the head are.
The guides can certainly be the cause of the vale seat wear.