Another U-Seal failure! - M104
 

When performing my headgasket repair (coolant corrosion), I found that the U-Shaped seal at the timing cover had split which was causing the oil leak.

At the time, I blamed it on too much silicone sealer in the area causing it split. Likely from a repair of the previous owner.

So, knowing enough not to put any sealer on the seal, I replaced the seal and only put a spot of sealer on the ends where it meets the cylinder head. No leak and I was happy.

Fast forward about 7 weeks. I started noticing a leak coming from the front of the engine and coating the air pump and alternator. However it was leaking at a faster rate than previous. I was expecting something more catastrophic, but not the case. The U-Shaped seal was split again in several places! This time with no silicone.

So, I wonder what could be causing this? If I recall correctly, I think I oiled the seal so I could get the cover on without rolling the seal out of its groove. I suspicion that the oil I used (engine oil) may have been contaminated with solvent and may have caused the seal to expand. Or maybe if memory doesn't serve me correctly, I didn't oil it and the small amount of expansion and contraction of the two covers could have caused the seal to split. In other words, I don't know what could be causing this seal to fail. Pictures below.

This time...
http://files.me.com/benzman35/efy522 http://files.me.com/benzman35/brs3nk

Last time...
http://files.me.com/benzman35/bf6tjd

Any thoughts?

7 weeks..

you sure you didn't roll over it, accidentally, causing a split.

i have only done one of these... and i think all i did was put a dab of the black stuff on the ends... practiced a few times before i did that to get the feel so i wouldn't roll over..

i was paranoid about that repair for awhile...but it held.

You know, I may have unknowingly rolled the seal upon installation of the cover.

Odd too, because I recall checking and double checking as I was tightening the cover.

Oh well, I guess I'll try it again and hope it doesn't blow out one more time.

Looks like the seal was rolled during installation--ask me how I know what that looks like........

Installation tip: reinstall chain guide pin AFTER cover is in place. The chain guide pin protrudes out further than the two cover alignment pins. If you install the cover with the pin in place, the starting position of the cover is further away from the block. This results in the bottom lip of the cover snagging the seal instead of sliding over top of it...... Again, ask me how I know......

J. M. van Swaay

This worked on my M103. I put the bead of benz black sealant in the corners as required, set the gasket, then I laid a piece of thin plastic sheet on top of the gasket (with a cut-out to avoid hitting the chain). The plastic was placed just short of the corner so it wouldn't interfere with the sealant. I slid the cover in place, finger installed the bolts and the carefully pulled the plastic out. It seemed to work okay as I've had no leaks after several months.

I did a dry run before using the sealant and with only a few bolts to see how it would work first.

Although others have used a Locktite product I recommend using the MB black sealant when replacing the upper timing chain cover U-shaped seal. As mentioned, only a small dab at the each end of the seal. I used it when I replaced the U-shaped seal on a 104 engine, and no more oil leakage.