The head gasket on my '91 300E is leaking in multiple places (have oil in the coolant, etc.) and it's time to replace it.

I have an official MB service manual that gives a great run-thru on how to remove/replace head and gasket on the 103 engine -- thus I'm pretty confident I can do this myself but I know it won't be done without a hitch.

Any chance a tech could chime in with some common mistakes/pitfalls that are encountered while tackling this job?

The procedures that appear to be difficult are removing the slide rail bolt from the timing chain guide (need an impact puller it says) -- and re-installing the chain tensioner (manual says that it must be disassembled prior to installation, unlike removal)

Some questions:

1. procedure says to lubricate head contact surface and head bolts prior to installing gasket -- sound correct? (instead of lube, clean sealing surfaces on valve cover, timing chain housing cover, and head front cover)

2. sealing timing chain cover involves placing sealing compound inside groove, then install the gasket in groove?

3. re-mounting the front cover radial seal requires a special tool p/n 103 589 00 14 00 (looks like a small round grommet) ?

4. disconnecting bowden cable -- difficult?

From what I can tell I'll need the following parts to do job correctly:

1. new head gasket - duh and head bolts w/washers
2. new timing chain cover gasket
3. sealing compound (loctite?)
4. new front cover rubber o ring seal
5. valve guides and seals

Engine has 205,000 on it, and is not burning oil, so I'm inclined to just replace the valve seals/guides.

Any input would be appreciated!

TIA

~Paul

Paul,

This was discussed pretty recently here:

300E Heads R & R What Else?

Don't forget a new valve cover gasket...

Have fun!

__________________
D.H.

04 ML500
02 E430

Experience is something you don't get until just after you need it.

Hah! Thanks Dennis ... didn't see that. Yes indeed, this should be fun.

~Paul

I just finished rebuilding my M103. So while I have things fresh in my mind...

I did not replace my valve cover gasket. There did not seem to be any reason to do so.

I also had no need to pull the chain guide pin. It was not in the way of anything.

I had a CLEAN surface on the head and the mating block surface.

Use anti-seize on all bolts.

You don't need a special tool for the front seal.

Use MB sealant A 002 989 73 20 10 for the lower and upper timing chain cover. The dealer has it and it is about $20 and weel worth it.

Do NOT use and sealant on the rubber gasket. Only where it contacts the block. The service manual covers this.

Use no sealant on the valve cover. Make sure the surfaces are clean.

Replace the chain guide and rails and unless you had the timing chain replaced in the six months or so, replace it. No questions asked. It's less than $40 and it will save you much more.

The chain tensioner is easy. The book also outlines that pretty well. There are also recent threads from my rebuild that discuss the process.

Throttle cable is not hard. (Oops, I mean bowden)

Good luck!

__________________
Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)

Thanks alot Michael .... that's pretty much all the info I was looking for where the manual was vague about.

:p :p

One last question however... how heavy is the head itself? Will I need a pulley to lift if off once it is isolated and unattached?

~Paul

Michael offers excellent advice, he's recently "been there and done that".

I would like to offer a little more. First of all I would not even think about replacing the head gasket without doing a valve job with new valve guides AND ensuring that there is no corrosion damage to the head. My M103 head exhibited the same symptoms as yours and it turned out to be the water jacket corroded through from lack of regular coolant replacement. My machinest welded it up.

When laying the camshaft back in place, it is important to start all bolts fingertight, then gradually tighten them all down a little at a time, if you don't do this, you could break the cam or strip bolt holes.

The tool for the seal that Michael correctly told you that you don't need, is substituted for by using a fingernail around the seal as you push the upper timing cover rearward into place. You are seeing that the seal does not "fold".

The importance of following the tensioner instructions cannot be overstressed. If you do not, you can break something expensive because you will be putting it back together with tension. Push the ratcheting plunger all the way through after removing the tensioner assembly, then start it from the outside, don't push it any further than just starting it into place. Upon startup, oil pressure will ratchet it into place.

You can do it either way, but I left the injection system in place, rather than pulling it off with the head. It worked very well for me, I had to remove and replace a few of the manifold bolts from underneath, but it was no problem. It was preferable for me to prevent ruiining some of the vacuum and electrical connections on the injection system.

Use the sealant that Michael mentioned on the upper timing cover. It is slick and allows you to push the timing cover rearward without disturbing the USeal below the cover.

Best of luck and keep us informed,

Paul,

For your first question regarding "lubricating" versus "cleaning" the mating surfaces: I'm sure you're right. It was probably a bad translation of the manual to English that ended up instructing you to lubricate. However, it would be worth an e-mail to the gasket manufacturer to ask if the gasket should go on dry.

If your valve cover gasket is more than a few months old I would order one. They're about 7 bucks for aftermarket and $12 for German-made. If nothing else it is cheap insurance that your job will go smoothly.

I'm sure you've read about using real MBZ antifreeze. I just picked up some yesterday and it's not cheap ($12/gal), but my local parts wholesaler supports the claims made here on the board. He said that he used to recommend Prestone or anything with anti-corrosion additives and that MBZ antifreeze was a rip-off. Now he has been listening to the local mechanics who say they use MBZ antifreeze in Hondas, Toyotas, and everything else. It is just plain superior. They also claim that a car can run 10 degrees cooler with it. Okay it's all anecdotal evidence, but for a few extra bucks I'm giving it a shot.

This has been a great thread!

__________________
D.H.

04 ML500
02 E430

Experience is something you don't get until just after you need it.

Thanks Larry!

I was going to mention the valves, but forgot to in the hast to complete my note at the time. I would get all new valves. The machine shop can grind and reseat them. I can tell the performance difference after my rebuild and I'm sure it was because of the valve job.

They can also pressure test the head to make sure you have no cracks etc. It cost me an extra $20.

It is very important that you tighten the 4 bolts evenly when putting on the rocker arms. When they start pressing against the cam lobe and therefore against the valve spring, there can be alot of pressure. It will want to cock, or tilt the rocker arm to one side and can pull the bolt out, stripping the threads.

The head and intake are rather heavy. I used a come-along held overhead by a 2x10 spanning the garage trusses the width of the garage.

__________________
Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)