86 735i

[cjsdad1]

Hi guys

I have a 86 735i with a blown head gasket. It has 167K on the car.
The car has been sitting for 4 months. I did a dry compression test and have 90,50,30,45,55,60 psi respective. with 4 rotations.
I did a wet compression test and got 120,90 then I stopped.

I thought I need at least 140 psi to make an engine run.
Does any one know what the compression on a 166k mileage car should be.

I think the bottom end is junk, just wanted to make sure.

[ettsn]

Compression is relative versus absolute. You want all cylinders to be within about 10% of each other. If that is so, you can get a feel for ideal psi by multiplying your compression ratio by 14.5 psi (1 bar). That will give you a ballpark ideal number. Keep in mind that the measurement process is not an exact science, so the balance between cylinders is far more important.

Decent M30s can be had pretty cheap by the way. Just go find a nice runner and swap it in. Not too difficult to do, and the motors are pretty common.

-Paul

[ettsn]

Also note that the bottom end contributes little to compression. That's more a function of the head, gasket, cylinder bore and piston rings than anything in the rotating assembly.

-Paul