drakon

Hey guys,
My 1995 C36 is having the second headgasket at 135,000 miles, never had a valve job (that I know of). Mechanic recommends I do it now (of course) but it looks pretty good to me.
What do you guys think?

BTW, I have a light blue 'puff' at peak RPM, and a light blue 'puff' after starting the car up the next day after driving the car hard, these are common signs of valve job needed right? The Pistons feel SNUG so I'm going to skip the rings this time around.

Sulaco

Could be valve job, but could also be slightly stretched timing chain.

Honestly, I've never ever heard of an M104 needing a valve job or a timing chain from normal use (translation: unless something catastrophic happened that nearly killed the engine).

That light blue puff at peak RPM is curious though. I can't explain that. So, valve job might actually come in handy. But I'd wait for some more experienced people to chime in.

Why 2 head gaskets? Also never heard of an M104 needing 2 head gaskets.

vinceC

Sulaco - The M104 has had head gasket problems.

OP - What is the need for the 2nd head gasket? Is it the oil leak issue that the M104 is known for? If so, that can be pretty much solved by using the right head gasket. I would have the shop get the gasket from the dealer to make sure it is the latest version. Some of the aftermarket gaskets don't hold up. Also, make sure the shop checks the head to make sure it is not warped.

The puff doesn't mean much if the plugs are staying clean and oil consumption is moderate. Generally, the need for a "valve job" is low compression, a burned valve or worn valve guides. Worn valve guides can cause oil consumption to rise. The M103 was known for weak guides (at least the first few year models) but I don't recall hearing of valve guide issues with the M104. I had a 1995 C280 (M104) that went 254,000 miles and didn't need any engine work except for a couple head gaskets early on when the various head gasket versions were being tried.

The pictures look OK to me (although larger photos with more detail would be useful).

Sulaco

vinceC, yes, I know. I've owned 2 of them. Did the head gasket myself. But never heard of one needing the head gasket job twice until now.

I also put 254k miles on an M104-powered C280. We should party.

But +1 to what Vince said. Nearly all cars will develop a puff at cold start.

But while you've got that head off, I'd spend a lot of elbow grease and thoroughly scrub clean the top of the pistons and bottom of the head/valves.

drakon

Thanks for the advice guys, I'm going ahead with the valve job, i'm not totally convinced it's necessary, but given the cost difference in doing it now, and the possibility of doing it again in the short term future I think I might as well do it.
Here are higher res pics:
https://www.dropbox.com/s/9uk1rr4ln9...2018.23.44.jpg
https://www.dropbox.com/s/efibc8iux9...2018.36.46.jpg
https://www.dropbox.com/s/v36h7ds6za...2018.36.18.jpg
First headgasket was replaced at 110,000 miles because the engine overheated on the freeway due to the radiator literally exploding and dumping the coolant on the freeway, unfortunately there was no shoulder to stop at, and the next exit was about 4 miles down.

This headgasket is being replaced at 135,000 miles because it is seeping oil at the front and back of the engine, and the coolant is seeping from a rusted cap on the head and the angle makes it very difficult to drill out.
The car is consuming oil at roughly 1 qt per 1200 miles, and the plugs are not that dirty but the valves look to be quite dirty on the top, I thought that was a sign for valve job time?
I think the car could have been driven awhile longer by getting creative, but I don't want to take too many risks as I drive my car hard, and it gets very warm where I am...plus traffic is really bad ALL the time.
I'd still like to hear your opinion, and if you think my mechanic is just taking me for a ride!
What is the 'right' headgasket? Its coming from the dealer, but this is Taiwan, so that's no guarantee that it'll be the 'right' part. I have my suspicions that the wrong or low quality HG was used the last time around...

Sulaco

Your logic is sound, might as well do it now! Much cheaper than doing a valve job in 20k miles.

Sounds like whomever installed your last headgasket used inferior product or method. Need to follow proper procedure when tightening the head bolts, AND USE BRAND NEW PROPER SPEC HEAD BOLTS.

IIRC: New bolts. Place head and gasket back onto car. Tighten working from the bolts in the middle and alternate sides until you've reached the last, outer bolts. Tighten to exact torque specified (I don't remember exactly what). I completed the car, and drove it for about an hour, I think, then took it home and removed valve cover to re-tighten head bolts. My head gasket job occurred at 150k miles and when I sold the car at 254k it was still 100% good to go.

I think any new M104 head gasket now will be the correct one. The originals in the 90's had weak points that would leak or cause really bad cross-flow between cylinders/water flow underneath. Newer ones are all corrected for this. Ever M104 on earth will need a head gasket at some point. Pity. Ended the legacy of one of the best I6 engines ever made!

vinceC

There are still bad head gaskets for the M104 out in the aftermarket. The fact that the OP has the oil leaks on a fairly recently replaced head gasket is evidence of that. Also, in following other M-B sites this issue turns up still. Having the right part number is no guarantee. Many aftermarket suppliers sell the inferior gasket with the correct part number. The only way I know of to be sure is to purchase from a dealer, in person, or online (some dealers have online or phone sales).

DRBC43AMG

If the head is off, I would recommend you get the top end done on this occasion. The puff of smoke probably is due to worn valve stem gaskets (I can't find the right word but it's a plastic thing which is placed on the valve stem, if they have them on that type of engine). Lapping the valves is the minimum, but if the valve guides are worn, you may need new ones. A bit expensive I imagine as you have 32 guides to push out and new ones pushed in...

unimoged

Did you do a cylinder compression check before taking the head off. Wet check will tell you if your rings are worn. A dry test tells you if the valve seats are worn.

Consuming 1 quart every 1 k miles is high for a straight six Benz motor.

Personally, if this was my car I would replace the piston rings to improve ring tension and insure that the oil ring groove (3rd ring down) is not gunked up.

Also, if the dry compression test showed no variance among the cylinders I would not do a valve job. I would just replace the valve guide seals.

Sulaco

This thread really makes me want a C36 for some reason.