Revised Leak Down Questions please help
 

1977 911S 2.7L

Recently had my engine rebuilt by a factory trained mechanic (he is the local Porsche guy and rebuild these all the time) it now has only 3500 miles on it.

The rebuild included new rings, replaced studs, rebuild on the heads, line bore etc.

At around 1,000 miles I noticed it starting to smoke and consume oil. Now it smokes considerably and if it is left for a week or 2 with out starting, at start up it fills the neighbourhood with smoke for at least 5 minutes.

Here is the data from the tests

Tested with engine much warmer, 10 minutes after full operating temperature. Leak test done first.

Leakage test / Compression test
#1- 45% / 115
#2- 18% / 145
#3- 38% / 145
#4- 35% / 140
#5- 20% / 155
#6- 20% / 145

What does all this mean and should the engine come apart again.

Your help is extremely appreciated. I will be taking my finding to my mechanic to get this resolved so I better be right!

Thanks and sorry for earlier confusion.

Paul

Those compression numbers look pretty bad, especially for a rebuilt engine. Did you hold the throttle wide open?

The leak down is instantaneous, meaning you see the results immediately. I set my compressor regulator to ~75 psi and leave it on. I set my pressure regulator on my leakdown fixture to 50 psi. Twice the difference between the two gauges on the leakdown fixture (using 50 psi) is your leakdown %.

I use a single gauge, similar to this:

http://www.650motorcycles.com/LeakDownTester.html

You set the gauge to ZERO with the air line disconnected. Make sure the compressor is ON so you have continuous high pressure and volume from its air tank. THEN you connect the pressure line to the cylinder. Make sure the engine cannot rotate. For a leakdown, it doesn't matter that the throttle plate is open, that's only relevant for compression testing, although you might be able to hear better.

The needle reads instananeously.

http://forums.pelicanparts.com/uploa...1112536862.jpg

Thanks John,

Would the picture you provided read as a 47% cylinder leakage or does it have to be calculated with the preasure side like I have read in other posts.

PK

BK, On the leakdown gauges when I set the leak down % gauge to zero my psi gage only goes to 24 psi. When I set the psi gauge to 50 the % gauge reads way past the 0/set mark. This is while not connected to the cylinder.

PK

PK, that's about 45% leakage. Was it accurate. You bet, see below.

http://forums.pelicanparts.com/uploa...1171291428.jpg

The pressure your gauge reads will vary depending on the orifice size. Lower pressure on the inlet side doesn't matter as long as it's a reasonable number, I think I saw 35 PSI on the inlet side. Just make sure the outlet side is zeroed out before you start.

The numbers are in. Tested with engine much warmer, 10 minutes after full operating temperature. Leak test done first.

Leakage Compression test
#1- 45% 115
#2- 18% 145
#3- 38% 145
#4- 35% 140
#5- 20% 155
#6- 20% 145

What does all this mean and should the engine come apart again.

Thanks
PK

Leak down test results started over.
 

I have restarted this thread due to miss information I provide from the earlier test. Thanks to those who replied.

1977 911S 2.7L

Recently had my engine rebuilt by a factory trained mechanic (he is the local Porsche guy and rebuild these all the time) it now has only 3500 miles on it.

The rebuild included new rings, replaced studs, rebuild on the heads, line bore etc.

At around 1,000 miles I noticed it starting to smoke and consume oil. Now it smokes considerably and if it is left for a week or 2 with out starting, at start up it fills the neighbourhood with smoke for at least 5 minutes.

Here is the data from the tests

Tested with engine much warmer, 10 minutes after full operating temperature. Leak test done first.

Leakage test / Compression test
#1- 45% / 115
#2- 18% / 145
#3- 38% / 145
#4- 35% / 140
#5- 20% / 155
#6- 20% / 145

What does all this mean and should the engine come apart again.

Your help is extremely appreciated. I will be taking my findings to my mechanic to get this resolved so I better be right!

Thanks and sorry for the earlier confusion.

Paul

With those numbers you should be able to hear where the problem is, listen to your intake, exhaust and case breather..

I'm gonna guess that the rings never properly seated since you have significant leakdown across the board. If you were too gentle or didn't break the car in properly this can happen.

Now Cragi's advice is sound. Hook up your air supply and listen (or put a rubber glove over) the intake, exhaust, and case vents. This should tell you where the air is going...

Most likely ring problems. There are many possible causes. Installing new rings on worn out pistons is probably the most common. Other possiblities are: Worn out cylinders, poor cylinder preparation, improper break-in, rings damaged on installation.

If these are Alusil cylinders the common wisdom is that they can fail even if everything is done right. I haven't seen this failure however.

-Andy