B.Kish

Wanted some advice on a potential 964 purchase.

I am having a bugger of a time getting useful and consistant advice on a PPI for these cars. Most places I call to do a PPI don't recommend a leakdown or compression on these cars (huh?). That's fairly consistant, believe it or not. And when I insist, they seem indignant. This has happened many times at many different shops.

Anyway, had a PPI done on a 1993 964 with 50K miles. At the advice of many (and to satisfy my own desire not to buy a lemon) I had a leakdown done. The first test came back from 5 to 14 percent. Hmmmmmm..... The guy doing the PPI and another mechanic who I trust(as much as you can trust a guy who needs to make a boat payment desperately) said not good, but may be carbon. OK...... They both recommended running the p*ss out of it and trying again, hot.

The new results improved, but not much (3%-12%). One mechanic said run, don't walk away. The other (who did the PPI) said "valve guide wear". I have no imput from the previous owner (oil consumption) as the car is being sold at a dealer. Tey guy who did the PPI says he sees this regularly in 964 motors and this one should last a long while before guides are needed. He did add the caveat that maybe the motor was down on power, but just a little. Thoughts?

I have read on this forum that a leakdown may not be worthwhile on a 964 and a compression is better. Thoughts?

Thanks for your time.

The car is very nice a unique and I'm not sure I want to give up on it just yet.

Carrera51

One thing I have heard about leak downs is that the motor has to be cool in order to get an accurate reading. Was the motor cool when they did the leakdown, or did they pull it in the shop and do it right after you drove the P&%$ out of it?

I also read on this board that carbon build up will effect the leakdown numbers. One person recommended running some Techron fuel additive through the motor before doing a leakdown.

I'd wait for someone with more mechanical knowledge than yours truly to chime in on this subject.

Kevin

Your leakdown should be within 5% of each other. And getting two in a row, might show a possible problem. If the mechanic said it was the guide he might be right. The pressurized air needs to escape somewhere, hearing it in the crankcase means failing rings, hearing it in the exhaust means failing exhaust valves, hearing noise in your intake tract, air filter box, bad intake valve. Your exhaust guides might be the ones at fault, which would cause the valves to not center correctly on the seats, which would cause the leak. If the engine was strong, you could run some techron to remove some of the carbon. 50K is low miles.

Jim Michaels

I don't understand why most have been advising against a compression check, but this case *may* be an excellent example of why some (many?) don't recommend leakdown tests for these cars.
The leakdowns have been said to be unreliable, in that they too often lead to the unwarranted conclusion that the motor needs work. No one that I've read has claimed unreliability in the other direction: i.e., that leakdowns too frequently lead to a passing grade for a bad motor. But it's too late not to have the test done, so everyone is stuck wondering if it's a bad motor or bad data.

If I had been in on all that, I don't think I'd be ready to say "run, don't walk away" just yet. First, I'd want the mechanic to elaborate on his "maybe the motor is a little down on power" comment. He didn't seem to be ready to conclude that the leakdown identified a motor problem, so what's he have in mind? Second, I'd want to talk with the previous owner and get the service and other history of the car. I think that should be done before the PPI; -it may save some time and money. If the dealer says they don't know who the PO was, and don't know anything about the car, then it's time to walk. Usually dealers' jump at the chance to tell you about the car's history when it's a local car they regularly serviced. If they bought the car at auction, well, they might not want you to know even that much. The truth is out there.

Fox Mulder

B.Kish

Well, the saga continues.

Getting all sorts of advice now how to get to the bottom of this...if I want to spend about $1000. Not likey on a car I don't own.

Have had several suggestions on a valve adjust and retest as well as running cleaner thru the fuel system. Another suggestion was to move on to a 993 (gee, that's a help). Of course, broker says leakdown numbers are OK and I've had three other people chime in that leakdown on anycylinder should be 5% max. While I would wish for that number, it seems unrealistic for a 50K car (or maybe even new).

I did get the service history. Nothing too out of the ordinary. Only fault was oil thermostat at approx 30K miles (did the car overheat?)

PO says zero oil comsumption, checked every 500 miles. Uh huh. I'm sure he has some oceanfront property in Arizona too. PPI mechanic says he saw evidence of some consumption.

Likely no sale. Need to be patient and wait for something better. Thanks for all your imput.

Brent

MikeF

As I understand, leakdown on a 964 is only useful as a price-negotiating tool. Most will show poor leakdown numbers...something about the shape of the cylinder head and the fact that it is a static measurement only...not a state in which the motor operates. Have a compression check done...if that shows OK, go for it.

For curiosity sake, if you find another 964 and have a PPI done, be sure to post the findings. Also, anyone out there have 5% +/- leakdown numbers on their 964? Honestly?

J richard

I have only found that leakdown numbers are really only useful in concert with a compression test and a comparison of value for each cylinder. The leakdown is usually used to determine the cause of a out of spec compression value. Because of the location of the valves in the cyl. It is very common for a bit of carbon to enter into the mix and cause a bad reading on a leakdown when the same cyl shows ok on a compression test. The difference is that a small peice of carbon can blow a whole leakdown, vs. a compression test averages four or five compression strokes. They are much less likely to be affected by a bit of carbon.

I don't think that a low value on a leakdown would be caused by a bad guide, more likely a bad seat/valve surface. The guide has very little to do with how the valve sits in a closed position, the valve head has a tendancy to self center in the seat due to it's conical shape, the spring holds it into position. Guide wear will usually show up in loud valves, excessive oil consumption and/or fouled plugs.

Get a compression test done, if it is within tolerances you are more than likely fine.

Regards

Kevin

J Richard;

I need to jump in and correct the fact that the valve guides do impact the way the valve seats. When you have a valve job done and use blueing dye, you will notice that the sealing ring of the valve to seat is less than a 32nd of an inch. When you have a guide that is wearing or worn out of spec that valve doesn't seat perfectly, it tends to rock to one side, it pounds the seat out and and that fine sealing area gets rounded, and does not keep the air in the combustion chamber. When doing a valve job many machinists will test to see if the valves have seated correctly by filling the ports with solvent. You should not have any leaks. If not fixed that valve will burn, and possibly fail. I have owned 911 engine that have had 3-5% leakdowns. It is not within reason to get those figures. There are guide issues with alot of 911's (3.2's-964's-993's) Steve Weiner and other well respected individuals have noted this fact repeatedly. It is better to explore all areas, rather than to get stuck with a unexpected valve job. A compression test is good for my Chevy, but if I'm going to spend some cash on a 911, doing a leakdown tells the condition of that engine. And in this situation two seperate leakdowns were done the carbon that might have lodged in the valve to seat area would have not shown up in the second test.

B.Kish

I would agree that bad guides can be the cause of these readings for the reasons Kevin mentioned.

Another thought is that if the guides are bad, not only will the seats get pounded but my thought is the oil will coat the seating surfaces of the valve and seat, hardening, and causing a poor seal also.

Here are some specs (leakdown and compression) of other cars:

This is a 93 which had a PPI done before I looked at it with 41K miles:
#1 6% and 160
#2 8% and 165
#3 4% and 165
#4 7% and 170
#5 5% and 175
#6 4% and 165

Here is a 94 I almost bought but the ODO had been tampered with it turned out. A supposed 40K miles (probably accurate mileage in hindsight):
#1 6% and 170
#2 4% and 175
#3 2% and 180
#4 2% and 170
#5 6% and 175
#6 2% and 175

Here is a 89 Carrera of a friend. 48K miles
#1 4% and 165
#2 4% and 165
#3 5% and 165
#4 3% and 170
#5 5% and 165
#6 3% and 170

And, of course, the car in question:
#1 12% first test 12% second (hot)
#2 12% first test 10% second
#3 5% first test 3% second
#4 14% first test 12% second
#5 12% first test 8% second
#6 10% first test 10% second

What a learning experience this has been.

I think the numbers could be used as a negotiating tool but the broker is steadfast in his feelings the numbers are OK. In other words, no discount. We'll see how he feels in a month.

Anyone have compression numbers for a 964 motor? My guess is 175 to 180 new.

Thanks again.

J richard

Kevin,B.Kish

Yes you are correct that the condition of the valve guide ultimately will affect the sealing ability of the valve guide, my point is that excessive leakdown alone without oil consumption or excessive valve noise should not automatically lead you to a guide. I have seen a two 911's with a valve "condition" that had to do with missed shifts and tweeked valves (for sale by the way). The guide wear, noise & oil, is usually noticed before the seat is gone. As far as the compression test, again it should be looked at in concert with a leakdown. What compression values did you get on the car?
My 93 runs 175-180 with 3-5% leakdown pretty consistently (unless I get a bit of carbon which is pretty obvious).

Hope this helps
Regards

B.Kish

JRichard,

I have, unfortunately, never seen(or heard)the car. It is several states away. I am trusting in the PPI and the information I am getting from the mechanic. You are right, this car is likely a long way from terminal seat damage.

I don't believe, for an instant, that this car (or most any other 911) "doesn't burn any oil" as the broker indicated.

I never bothered to gather more information such as a compression test because it just started to become not worth the time or expense. The car had to go back to the shop and more time and $$$.

The seller and broker never bothered (not that they should) to try to get more information or clarify the results in an attempt to make the sale. They continued to claim the leakdown numbers were within spec (even though they call repeatedly to see if I'm still interested-guess they haven't sold it).

I'm sure they would suggest or do a compression test or something if they felt the tests already run were in error. They don't say they are in error. They think a 12% leakdown is normal. It's not.

Better luck next time. And for sure a leakdown AND compression.

Many Thanks.

johnfm

Feel sorry for you guys in a way. This seeems like a hell of a lot of trouble to buy a 964. I found a '92 C2 Tip with 80k miles on clock. Drove it & got very excited. So, I had independent Porsche garage look at it. They identified £1300 of immediate spend on brakes, oil pipes & front wish bones. I knocked seller down from £18k to £16k. Bought it in 2 days! What a fantastic car. Maybe I've been lucky ( I am touching wood as I type)but you guys in the US seem to have a huge distrust of sellers and the cars they are selling.

Maybe, you could try not getting so hung up on the numbers. Find an experienced mechanic that you trust and 'use the force'! Best of luck getting a 964!

SteveW@stig

Just remember that the 964 is known to have valve and piston ring wear problems as the mileage goes up. Really depends on what sort of life the car has had as to when the wear becomes significant. Anything with 50k plus is getting ready for a rebuild if it has spent a lot of time in town traffic, up to 100k if it has had an easy life.


[quote]Originally posted by B.Kish:
<strong>Wanted some advice on a potential 964 purchase.

I am having a bugger of a time getting useful and consistant advice on a PPI for these cars. Most places I call to do a PPI don't recommend a leakdown or compression on these cars (huh?). That's fairly consistant, believe it or not. And when I insist, they seem indignant. This has happened many times at many different shops.

Anyway, had a PPI done on a 1993 964 with 50K miles. At the advice of many (and to satisfy my own desire not to buy a lemon) I had a leakdown done. The first test came back from 5 to 14 percent. Hmmmmmm..... The guy doing the PPI and another mechanic who I trust(as much as you can trust a guy who needs to make a boat payment desperately) said not good, but may be carbon. OK...... They both recommended running the p*ss out of it and trying again, hot.

The new results improved, but not much (3%-12%). One mechanic said run, don't walk away. The other (who did the PPI) said "valve guide wear". I have no imput from the previous owner (oil consumption) as the car is being sold at a dealer. Tey guy who did the PPI says he sees this regularly in 964 motors and this one should last a long while before guides are needed. He did add the caveat that maybe the motor was down on power, but just a little. Thoughts?

I have read on this forum that a leakdown may not be worthwhile on a 964 and a compression is better. Thoughts?

Thanks for your time.

The car is very nice a unique and I'm not sure I want to give up on it just yet.</strong><hr></blockquote>