Compression numbers

[S54ATL]

Looking at a 540 (yes, Nikasil). Compression/leakdown results came back like this:

Leak down: Cyl #1,2,3,5,6,7 & 8: 10%
Cyl #4: 15%

Compression:Cyl #4: 130psi
Cyl #1 & 5: 135psi
Cyl #3, 6, & 7: 140psi
Cyl #2: 145psi
Cyl #8: 150psi

Everything I've read says that the compression should be north of 180-185; clearly these are well below that. My questionss are:

- Is it possible the test was done incorrectly (REALLY incorrectly)?
- Would an engine even run in this condition?

The owner has been really open about the car (including what he perceives the problems to be), and seems like a very honest guy. He says it runs awesome and is very quick - let's assume for the sake of argument that he knows what "very quick" is. Could a motor with these numbers be "very quick", or would it be sputtering along on it's last leg?

[David325e]

A motor that is down on power because it is losing compression can still run. But compared to a well running 540 it'll be severely down in power. Any leaks/etc to indicate bad head gaskets?

[S54ATL]

The car is not local, so I haven't "seen" it. He says it doesn't leak a drop.

[kalevera]

BMW says max permissible leakdown is 15%. Compression is out of spec if there's a 10% difference between cylinders, or below 135 psi. The numbers could be low because the engine wasn't warm when the tests were done.

[jac1d]

I answered this one in email but I'll repeat here for the benefit of future searches.

Both the 525 and the 540 we recently bought tested at 200+ psi across all 6/8 cyclinders. The 540 is an original Nikasil block with ~145K miles on it. Leak down was 0-5% on all but one cyclinder that had 10%.

The car (530i) that we passed on had serious leak down issue and lower than normal compression. You can see the table on page one of this document:

http://dl.getdropbox.com/u/161739/1995%20530i%20E34%20PPI%20Sample.pdf

Even then the compression was in the 170s mostly (I misspoke in my email, I thought it had been even lower). Yes, the leakdown is an even bigger issue but I would be very concerned about compression down in the 130s which it should be 195+ on a healthy engine. You will also notice the variance is quite wide at 167 to 200 on that 530i test. Thats about 20% difference.

At a minimum I would have it retested. And if you have the luxury, I'd test another 540 in your area (at the same shop/method) and compare the results. My spidey senses tell me to stay away, especially since you can't see the car.

Who did the compression test?

-Jeff

[S54ATL]

Good info (thanks). Anybody else care to chime in?