A New M104 Oil Leak: "Thrust Pieces?" - PeachParts Mercedes-Benz Forum

jcyuhn · #1 03-08-2009, 09:53 AM

Hi All -

I have an innovative new oil leak on the old M104 engine. It's seeping around the so-called thrust pieces. These are the little rubber doohickies which MB uses to seal the bolt holes which secure the valve cover to the engine. In a particularly impressive bit of German engineering, the most leaky one is near the transmission dipstick. The oil seeps by the thrust piece, down the edge of the valve cover, along the head, out the transmission dipstick bracket, and down the transmission dipstick and onto the garage floor.

Any advice or comments on replacing these? Does the valve cover need to be removed, or are they replaced in situ? Any special tricks? I'm hoping it's as straightforward as it appears.

Thanks,

- JimY

J. M. van Swaay · #2 03-09-2009, 11:45 AM

Are these what you are referring to? If so, easy fix--about 30 minutes. These little rubber squish washers get hard and brittle over time. This results in not enough "hold down" force for the valve cover gasket to seal properly. Picture shows old next to new. Note the old is permanently compressed, hence the less "hold down" force. If I remember correctly, there are three of these under the coil cover--easy to forget because you don't see them.

Maybe your leak is the result of a torn/cracked squish washer?

Hope this helps.

J. M. van Swaay

jcyuhn · #3 03-09-2009, 02:40 PM

Yup, that's exactly them. Didn't think to call them "squish washers"

OK, looks like an easy replacement. No need to pull the valve cover - super!

No leaks at the valve cover gasket, only the squish washers themselves. Most just show a bit of oily dirt accumulation, but one is letting out enough oil to run down the side of the engine and drip a bit on the ground.

Thanks much!

- JimY

J. M. van Swaay · #4 03-09-2009, 07:29 PM

Just a tip, don't over tighten these bolts. They thread into an aluminum head and strip easily. An unaware mechanic will sometimes try to get a leaky valve cover to seal by torqueing these down harder. The hold down bolts have a shoulder that rests on the top of the head. (easily seen in the picture) More torque does not equal more hold down force, but may result in stripped threads. Only new "squish washers" (yes, a very technical term....) will provide the proper hold down force. On one of my 104s, I had to put in several heli coil inserts to repair damage by a previous mechanic.

J. M. van Swaay

johng99 · #5 03-10-2009, 02:26 PM

I just had the headgasket replaced on my E320 by the dealer. A week later I was leaking oil again, and a lot. I returned the car to the dealer, only to find that they had not replaced these washers, and the valve cover gasket had shifted. They replaced and also replaced valve cover gasket, and now, no leaks. I hated to take to dealer but this was one job I was not prepared to do myself and one of the local shops was a big dodgy on committing to cost of the repair.

J. M. van Swaay · #6 03-10-2009, 07:17 PM

The dealer technicians should know better.................

J. M. van Swaay

johng99 · #7 03-11-2009, 09:48 AM

I agree. This dealer is not the best, but my indie recommended in this case, as he is too old now to do this work himself (he is over 65 and works out of his home these days), and he said that if "they mess it up, they will take care of it" which they did. Their price was actually competitive, so I only had to deal with taking it back to redo. On the second try they did keep the car a few days to make sure there were no more leaks, and after a few weeks of driving I am not leaking a drop.
Oh well, it is a really nice car that was dealer maintained for most of its life. The wiring harness is new, and now with a new headgasket I am planning to drive it for several more years.