My engine was reringed less than 2K ago. A leak down test was done today and we got the following numbers:

#1: 8%
#2: 12%
#3: 20%
#4: 24%

The mechanics said the progression front-to-rear is not unusual, but the numbers are not what I'd expect given the recent work. They suggested that the rings may not be fully seated given the low mileage since ring job (<2k) and the fact that I used Mobil 1 during the break in. (To be fair the car has only been driven occasionally and lightly around town since the motor work was done.) Jon, thesenior guy there, believes that the factory moly rings often take up to 10k miles to fully break in.

So, I'm going to drain the Mobile 1, put some dino in there and drive the **** out of it for 1000 miles and retest. There is no smoking, blow by, and the intercooler has no residue. No noticable oil use either.

Anyone out there had this happen?

George

 

24% - hahaha that's good one.
they screwed up the test.
The 951 engine is low compression and loves to roll over under a compression test - this will crack the valves open enough to give a stupid reading like 24%

You need to take this to someone who knows what the hell they are doing - and they need a flywheel lock too.

 

ST i'm coming your way so i'm lookin for you and the dyno

 

Yup, if you had 24% leakdown your engine would run horridly, and produce very little power.... you would most likely also burn a heck of a lot of oil.

Get them to lock the flywheel, and make sure the intake/exhaust valves are closed when testing.
Did they tell you where the pressure was going?

 

I'd still get the Mobil 1 out of there and run with Dino oil for the next couple thousand miles. Probably should have started with good old NAPA break in oil.

 

Thanks for the good news. I'll change the oil and flog it for a while. I'm picking it up in LA this Friday to drive it to Arizona where it will be staying. My local mechanic and I will do the test here.

I was not there when the test was done in LA. I just got the results.

George

 

Its the lesser of 2 evils with that first mechanic, man. If they really are that inexperienced - who wants them......and if they INTENTIONALLY screwed up the test to drum up work - that's worse.

Either way - no way in hell you have 20 an 24 and zero oil consumption and/or decent running car, no way.

 

How many miles were on the engine when rebuilt? Any cylinder scoring, any cylinder wear measurements taken, piston ring gaps? I doubt the shop used actual Porsche OE 951 rings, they are around $500 for a full set. My guess is that they either used 944 n/a rings (not a good idea since the top ring is not hard chromed like the 951 rings are), or used Goetze aftermarket 951 rings (should be fine). Regardless, I find it hard to believe that it should take 10k miles to properly seat the rings.

There can be a lot of error in a leakdown test - I dont think its the pefect "one all/tell all" test for engine condition. It is better than a simple compression test, but still leaves a lot of unknowns.

Most leakdown kits I have seen use just an air compressor type hose with a threaded fitting and an o-ring. You have to thread it into the head by hand - no way to get a wrench on it, and the o-ring will not hold 100 psi; so much of the leakage can be past this seal.

I had 3 leakdown tests run on one engine, by two reputable p-car shops and the 3rd I did myself. None of the results were even close. One shop said the motor was perfect, no more than couple % leakdown an any cylinder, the other shop said the motor was shot and gave me really high numbers. My own test gave me numbers inbetween. I ran my test several times, with the motor hot and cold, and got very repeatable results, but again, my numbers were not close to either professional shop.

If the shop's test numbers are accurate, the motor will still run with 20% leakage on a couple cylinders. It will be somewhat flat in the low rpm range, but under boost it may still feel ok. Why did you have the leakdown test run after 2k miles, was it not feeling right?

As far as using a synthetic for break-in, Im not sure thats a big problem. I have heard both ways. One shop owner does recommend dino oil and easy driving for the first 1000 miles, and another engine builder said that after a rebuild, he waits till the engine oil (synthetic is fine) is warm, then beats the snot out of it to seat the rings and bearings. Both guys build some strong motors. But again, these are the two shops that gave me polar opposite leakdown results, so who knows.....

 

The rings were factory moly. There was no scoring, none. The re-ring was done at 118K on a stock perfectly maintained 89 951. The engine was done because of the extensive modifications being done at that time.

I'll give an update as the car is in LA and I'm in Arizona. I'm flying there Friday and driving the snot out of it back to AZ. I'll redo the testing here.

 

I am not sure your leaking that much. Porsche uses syntheric oil from the factory, so that should not be a factor. I know the the original engines did take a long time to seat properly. A good friend of mine that works on a local P-shop, once toll me that on 944/968/928 engines it can take up to 40k before it is fully break-in.

Who did the break-in proccess?....was it the shop or you?

If you dont know , this is what I would do. Find a nice long empty road, and do acceleration runs (12-15 times) in third gear from 30mph to 60,65 mph. Full throttle and when you get to 60, let the engine vacuum slow it down to 30 and do it again. If you have a MBC/EBC turn it to the lowest setting. that should make the rings nice and square against the cylinder walls.


Regards,
AL

 

The numbers seem a bit too high... but I've heard of people who just re-ringed without honing the block and got fairly high leak down.

 

FYI when I did mine last year it was 2 ,2, 3 ,2

 

I've got to say that I don't believe the numbers. I'm going to run a test when I'm in LA after dyno tuning the mafterburner.

I have an 800 mile drive from LA this Saturday morning. I'll give it a good flog all the way.

George

 

I would almost think that those numbers could be achieved without compression rings. Last I measured, mine were also 2% - 3% - 2% - 2%.

I would recommend doing a compression test as a sanity check.

 

i've had this happen before too, you can do it without a flywheel lock but you just have to be very precise.