Reading Compression Report of my W124-E220(M111.960)
 

Hello All,
I am restoring recently bought 1995 W124-E220 (M111.960), got the compression check done at local Mercedes dealer, the report is as below

Cylinder Compression
-------------------------------

1 -----> 9
2 -----> 8.5
3 -----> 7.6
4 -----> 9

The engine has done about 70, 000 kms on ODO meter, I am slightly concerned about the compression reading of the cylinder 3, do I need to worry? What could be the reason for the compression drop, should I do some more checks? The exhaust is clean without any trace of smoke.

According to WIS this particular model compression is between 7.5 to 10.5(fuel optimized), please see attached image (Stock-Compression.gif). I have also attached actual compression image (Actual-Compression.gif), sorry for poor quality of the picture.

Thank you

Did they perform a wet test as well?

Did they run a test with air to determine the source of the loss...intake, exhaust or sump?

This will tell if its valves or rings.

If its valves, which seems likely, a valve job would be in order sometime, but if its in tolerance I probably would keep driving it for a while while I saved money.

You never know, you could spend thousands on a valve job and the next time out the car might be totalled in an accident.

Tom W

But then you still have a good running motor you could drop into a car with a bad engine. :D ;)

I have updated the Actual Compression image with better quality one if someone wants to have a look.

Thanks for the input all, no leak test has been done yet. I am not sure about the wet test, will check on my next visit to the dealer. Presently planning to run it for sometime while I save, then decide on valve job, may be new engine would be cheaper option?

Will update this thread on that.

You're fine, stop worrying about it. Look on the bright side -as said you're probably going to be in an horrific accident before it goes anyway.

After 92000 KM
 

After 92000 KM I had to re-check the compression due loss of power and overheating when revved.

Dry Cylinder Compression in Bar
------------------------------

1 -----> 6
2 -----> 5
3 -----> 4
4 -----> 5

Wet Cylinder Compression
------------------------

1 -----> 8
2 -----> 7.5
3 -----> 7
4 -----> 7


From compression reading, I am guessing I would have to replace rings?

- What could be the reason for huge drop in compression for some 20K kms? (see my first post for original dry compression)
- I don't see any smoke in tail pipe nor I am loosing oil.
- I have repeated the tests twice between 1000 kms and results are same as above.

I'm a little late to the game... why did you buy the car?

The compression numbers should all be within a bar. THere is more than just a "range", but they must all be close in the big range. And with low mileage, I'd expect them all to be around 10.

You need to do a leak down test and see where the leakage is..

Over heating...??? That's not good. How hot did you get it? Could have just warped valves and need a valve job. If you got it really hot, it's quite possible the rings have lost temper and gotten soft. You'd have to pull it apart and inspect the bores closely with accurate measuring equipment to know if re-ring is an option. Ussually, I'd say bore it and put o/s pistons in the block.

Michael

Or you could find another engine. If you're in Germany, could it have been a taxi with an odometer rollback? Some people are pretty good at that there.
If you're going to fix it, I would do both rings and valves - it's only a 4-banger.

Thanks for the input, will look into possible options, I am leaning towards another engine if I can find one.

- If engine is not in 5th gear (5 speed manual) the engine temperature is always around 100 - 102C, this does not vary much with external temperature. When cursing in 5th temperature will be around 90 C.

- Engine over heated twice in 20K km, with temperature hitting ~< 120 C (only for brief period), once when tension-er pulley broke and other time main fan had issues.

Will the above lead to rings loosing temper? What are the other possibilities that could lead to worn rings or cylinder wall?

120C is not extreme. Other causes could be sticking rings caused by oil sludge buildup, cylinder scoring caused by oil starvation, carbon buildup on valve seats (seems less likely due to your wet results). Infrequent oil changes can shorten the life of the rings as well.