Factory Compression Numbers

[Timothy Shiben]

I would like to know the factory compression numbers for a 119.975 engine, for my 92 400E when it was new. My 400E now has 96,000 miles and is there a factory guideline that estimates what the appoximate compression should be on an engine with this milage, if so what is the estimate compression number.

Thanks, Timothy

[GeorgeMurphy]

Originally posted by Timothy Shiben
I would like to know the factory compression numbers for a 119.975 engine, for my 92 400E when it was new. My 400E now has 96,000 miles and is there a factory guideline that estimates what the approximate compression should be on an engine with this mileage, if so what is the estimate compression number.

Thanks, Timothy

From the MB Tech Data Manual 1993:

Your compression ratio is 11 to 1

The highest ratio given in the compression pressure table is 10.5

New engine should be 14 - 16 bar; wear limit is 12.5 bar. Cylinder-to-cylinder tolerance is about 10%, (1.5 bar)

[Timothy Shiben]

Thanks George for the information, I was concerned, but I'm not sure what the diagnosis really is. I did a compression test and the cylinder tolerance is okay, but my average is 12.3 kg.

Compression by cylinder- (5=11.9) (6=12) (7=12.1) (8=12.1) (1=12.7) (2=12.4) (3=12.4) (4=12.3).

Procedure used, I used a NAPA KD Tools compression tester, warmed up the engine, not positive about this -92 400e fuel relay is under rear seat P/N 0015425919, I unplugged this relay, disconnected the dist wires, gas pedal to the floor, did the test 4 times.

I've been told consistencies across all cylinders are the most important numbers, however I'm at the wear limit, what to do next, a minor or immediate concern, recommendations please.
Thank you, Timothy

[GeorgeMurphy]

Unless the engine is running rough or seriously down on power, I wouldn't worry about it. The cylinder rings hardly wear in these cars with the silicon/AL alloy block and chrome rings.

A wet test will confirm if low compression is due to valves or rings.

Squirt a tablespoon of 30 wt oil in the cylinder and see what the compression reading is - if almost the same as dry test - valves are leaking. If sunstantially higher, then rings are leaking . . .

[Timothy Shiben]

Squirt a tablespoon of 30 wt oil in the cylinder and see what the compression reading is - if almost the same as dry test - valves are leaking. If sunstantially higher, then rings are leaking . . .

I will do the test, and yes I will probably have more questions.

George as you have over the years, Thank You for sharing your wealth of knowledge, Timothy