PeachParts Mercedes-Benz Forum - M103 head gasket re-torque

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Most interesting, thank you for posting.

Just curious, I'm threatening to try this, myself. Did you drain coolant and totally loosen all bolts, or just crack them one at a time?

Quote:

Originally Posted by MCallahan (Post 3815472)

Just curious, I'm threatening to try this, myself. Did you drain coolant and totally loosen all bolts, or just crack them one at a time?

There is no need to drain the coolant or oil.

Do one bolt at a time starting with the center ones and working outward.

Head bolts don't work loose, the gasket crushes resulting in a reduction of bolt tension.

The cracking sound you hear when breaking a bolt loose is from metal sort of cold welding to metal. The surfaces are rough and the peaks are pressed into valleys over time. Sometimes it is soft plating that gives the effect of adhesive. ( 80's Japanese automotive bolts were good for this and rarely rusted into place. )

Thanks, will give this a shot. Rear passenger side oil drool.

Thought I'd post one more update: been 20 months and 12k miles since the re-torque.

This last winter we had a couple of cold nights in the twenties, and I did notice a very slight mist of oil under the head behind #1 cylinder, where the blind oil gallery is located. I wiped it off, and it hasn't returned at all.
Obviously it was the result of the cold temps.
I suppose it will probably return again this winter, and eventually get worse than just a small stain, and I'll have to replace the gasket. But delaying the project a few years was certainly worth the effort.

And more importantly, understanding that re-torquing is a safe, effective process, I think I'd definitely recommend it as a routine maintenance chore every few years. I bet a new gasket would stay dry much much longer.

Cheers,
DG

I just re-torqued my head bolts as well after reading this because I was burning coolant in the #2 cylinder and could see coolant residue on the side of the exhaust pipe. I have about 63k miles on a Reinz head gasket that I replaced in 2023. I will monitor my coolant level over the next few days.

Quote:

Originally Posted by S-Class Guru (Post 3765848)

Procedure:
I marked the head of each bolt at 12:00 o'clock with typing white-out, and removed/replaced one bolt at a time, starting at the left center and working out in each direction.
I cleaned and oiled the head surface under the bolt, checked the depth of the hole, cleaned and oiled the bolt, and reinstalled, torqued to 40 ft lbs, then turned it 90 degrees ( after doing all 14, I then went back and turned them all an additional 90 degrees in sequence).

Just to clarify - you loosened one bolt at a time and then retorqued it? Then you moved to the next one diagonally across and loosened and retorqued it? Then removed the next one in the sequence and retorqued it? Till you do the corners last?

Sorry I may be interpreting your description incorrectly. This is really great how you did this and it worked out. I have just bought an M104 powered car that has obviously had its gasket replaced in the past. I’ve made a mental note of doing this Hail Mary move before I need to change a head gasket.

This reminds me of the oil filter housings on my om617/6 powered cars. Every one gets the leak at the housing. The cure is to pull the housing and swap the gasket. I’ve cured the leak on three of my cars just by tightening the bolts. I just tighten them clockwise and they crack free then they’re loose for about a 1/4 turn which is a lot. After torquing the four bolts it always stops the leak. Clearly the gasket is just collapsing. It only takes a few mil of collapse on the gasket to detension the bolts.

Great workaround. Thanks for posting the updates too because your long term results are validating.

I can't say for sure that it completely eliminated the leak because after I re-torqued it, I did a completely flush on the system and decided to pull out the thermostat and run a bottle of liquid glass through the system. I then drained it all out and flushed, then replaced the expansion tank, new thermostat (previous one was stuck open), and added fresh blue coolant to the system. No more leak at cylinder 2, though I'm not exactly sure if it was the liquid glass or the re-torque. At any rate, the problem is fixed. Thanks.

Quote:

Originally Posted by S-Class Guru (Post 3765848)

Well, I've been habitually plagued with head gasket oil leaks over the 26 years of fun with my '91 300SE. Got the dreaded rear passenger side leak again after only 5 years and 45K miles since a new Reinz gasket.

So......... I decided to go ahead and re-torque the head bolts. What the heck, what's the worst that could happen (I tried not to think about it).

Finished it up today, I'll report back in a few days or so to report if it actually stopped/slowed the oil leak.

But, I observed some things when I did the job that I thought might be of interest.This was only a minor oil leak, no coolant involved that I could tell, and good compression, so maybe it was a good candidate.

Procedure:
I marked the head of each bolt at 12:00 o'clock with typing white-out, and removed/replaced one bolt at a time, starting at the left center and working out in each direction.
I cleaned and oiled the head surface under the bolt, checked the depth of the hole, cleaned and oiled the bolt, and reinstalled, torqued to 40 ft lbs, then turned it 90 degrees ( after doing all 14, I then went back and turned them all an additional 90 degrees in sequence).

Observations:
These bolts have been re-used 3 times over the years. They measure exactly 102 mm; absolutely no measurable stretch, no indication of necking. Mercedes says to re-use them, i think it's pretty safe.

All the bolts behaved exactly alike. Each bolt was hard to break loose, making that lovely snap sound; obviously none had come unscrewed or loosened excessively.

After breaking loose, they quickly became finger tight after less than 30 degrees of rotation. Obviously not a lot of clamping force left here.

When I re-installed the bolt it returned to exactly 12:00 o'clock with only 40 ftlbs or torque. So, again, not much clamp left

When I turned the bolt the first 90 degrees, I used a torque wrench just to see the approximate force - about 75-80 ftlbs for this first turn.

When i made the last 90 degree turn I set the wrench on 90 and it didn't click. Tried the next one at 85, and it clicked just as I reached the 90-degree turn. So, I ended up with about 85 ft lbs on torque after the last turn. All bolts went down smooth and linear, could feel they were in the stretch zone.

Big interesting thing: I ended up turning all the bolts an additional 180 degrees from where they were when I started. That's .875 mm, or about 35 thousands! That's a lot of gasket compression or bolt stretch, or something.
Probably a combo of gasket, a little bolt stretch, and a little recession of the head under the bolt.

Anyway, I'll see if it works, hope to dispel a few myths about this all-to-common issue.

Oh, here's a little info on the source of these head gasket leaks.
The 103 head receives ALL it's pressurized oil from a passage right next to the RR head bolt. Thus the source of the worst of the leaks. There is no oil passage in the front of the head, but there is a blind one drilled in the block next to the RF head bolt. It's a blind hole covered by the head surface, but oil pressure is there and works on the gasket eventually, just like the rear passage. The front timing cover is, of course, another chapter in the saga.

More later, wish me luck,
DG

When replacing a head gasket on any of those troubled engine , assuming you clean the 2 surfaces good , use a bead of high quality silicone glue . That usually fix that . Another design flaw on those engines that was never dealt with .