E30 Zone

Hi all, just done a compression test on my 325i sport m20b25 and I'm getting 180psi across the board.

To me that's a little bit high. It might be a gauge issue, gonna test with another gauge.

Test was carried out on a cold engine, valve clearances done just before test.

Does anyone know what they should be.

Cheers

ping wrote: ↑

Sat Aug 10, 2019 12:20 am

Hi all, just done a compression test on my 325i sport m20b25 and I'm getting 180psi across the board.

To me that's a little bit high. It might be a gauge issue, gonna test with another gauge.

Test was carried out on a cold engine, valve clearances done just before test.

Does anyone know what they should be.

Cheers

Have a look in the "wiki" mate, I`m sure you will find something in there.

Mart.

160 ish is not uncommon. your results seem fine/good. i wouold not worry some guages read different

180 psi sounds very healthy - I wouldn't be worrying about it!

It will, of course, depend anyway on whether yours is the earlier high compression (25 6E) engine or later facelift low compression 25 6K engine...

I got 205 psi across all cylinders on my preface 325.

My compression test values a few months ago, warm engine, throttle open (WOT) and fuel pump relay removed:

Cylinder 1: 170 psi
Cylinder 2: 163 psi
Cylinder 3: 165 psi
Cylinder 4: 165 psi
Cylinder 5: 163 psi
Cylinder 6: 163 psi

The Bentley manual shows 142 psi to 156 psi to be normal/healthy. I maybe off 1-2 psi here or there, since the compression gauge reads in bar and in 0.2 bar increments, exact numbers are tricky with the gauge i have, but numbers are still good.

i ams till hunting down the slight misfire when cold and warm, maybe a valve is too tight, or more than one, unsure, it does sound mechanical rather than sensor/fuel.

Do these number sound right for 10/1985 build M20B27? It's all stock, no mods and well maintained over the years. I bought it from an uncle in 1997. He had the head bolts replaced sometime before I bought it.

#1 190 lbs
#2 175
#3 185
#4 185
#5 185
#6 183

Yes, all pretty healthy. You could try a squirt of oil in Cyl No.2 to see if it raises the compression up a bit...