Low compression on two cylinders ? - 91' 325i

[E-Terdy]

Hey folks,

While conducting a compression test just for the sake of knowing what kind of shape my motor is in, I discovered the following results:
Cyl. 1 - 130 psi, Cyl. 2 - 150 psi , Cyl. 3 - 100 psi, Cyl. 4 - 150 psi, Cyl. 5 - 150 psi, and Cyl. 6 - 150 psi. (1-6, from fire wall -> rad)

What I know about the engine:
-Stock M20 250'000km, retimed at 200'000km, Chip tuned by unknown company.
-Burns a hardly notable amount of oil (no blue cloud at startup/ under WOT), -Regular changes every 5000km with synthetic blend Castrol GTX 20w50 + oem filter.
-Oil isn't cloudy, Coolant revisior has no oily residue inside.
-No smell of gas when valve cover cap is removed
-Slight oil leak running down the side of the block. Never drips, but looks wet.

What are potential causes of a slight compression drop in one cylinder, and a larger one in another? There is a good cylinder between the two, so i dont think its a head gasket issue. I ran the test on the two bad cylinders three times each, always removing the tool, checking it, and reinstalling to rule out user error.

Any input is welcome !

-Rob

[jlevie]

While a problem with the rings on those cylinders is a possibility, the low compression could be from the valves. As a way of gathering more data, squirt a bit of oil into each of the cylinders and check compression. If the results are better the rings are bad. If little to no change the cause is in the valves. A leak down test can also be used to identify the cause.