Wednesday, May 15, 2013


When we last left our hero his 1978 Mercedes-Benz 240D was down for the count with a failed head gasket. What to do, what to do? Call out the troops of course! Saturday three of my good Mercedes friends came over and the four of us got to work.

I started before the others arrived, at about 7:30am I started by pulling the washer fluid bottle, radiator, hoses and radiator shroud plus the air cleaner and its hoses. Finally I disconnected the battery. My friend Fred arrived and we had breakfast. While we were eating Dimitri and Dwight arrived, with our team assembled we went back out and really got going. The air conditioning compressor gets moved out of the way but not removed. Mercedes recommends pulling the power steering pump out of the way but I didn't want to deal with the mess so we just pushed it out of the way, same for the oil cooler. With the front of the engine exposed the fan and its pulley get removed, all the belts are now out of the way. The thermostat housing comes off, then the injection lines, glow plug wiring.
Throttle linkage injector return lines and injectors which leaves the valve cover.

With that removed we see the cam shaft, timing chain and lifters, and Dwight's finger :)

Getting the head off and not screwing up the timing was one of our top goals so we spent a lot of time mucking about. It turns out you cannot leave the top sprocket on and remove the head, don't even bother. Fortunately as long as you maintain tension on the timing chain you can lift the head off without changing its alignment on the bottom end. A couple friends are helpful there.
So pull all the head bolts, put them in a piece of cardboard to keep them ordered.

The pull the head, its not super heavy but a helper here is a great idea, an engine lift would do the job too but is probably overkill.

Now clean the mating surfaces of the head and block real good. We scraped with razor blades to get a good clean surface, then ran a wire brush in the drill over them to be sure. We also cleaned all the headbolts good with a wire wheel. These are the hex head bolts which can be reused, unlike the later type which are torque to yield. Fred measured bend in the block, its slightly banana shaped which is normal. Mine is between 0.003 and 0.004 which is well within spec.

With everything cleaned a coating of Hylomar on the mating surfaces:

Thats some interesting stuff, it ate right through my gloves...

Re-install the head and torque it down. Theres a procedure for that of course...

Tighten, tighten some more, wait 10 minutes, tighten some more. You end up at 100Nm, a good long torque wrench is nice.

The rest is reversal of dissassembly which of course leaves out all the fun. Getting the timing chain back together was a bear, we probably wasted an hour on it. First we got the sprocket on but forgot the top guide, then we got the sprocket on backwards. FINALLY we got everything on and in the right orientation, I spun the engine over with a ratchet a couple times to prove it was all going in the right direction and nothing hit or made bad noises. Dwight and Dimitri had to head home, I can't blame them, they both drove many miles to be with me. Fred bless his soul stayed until the bitter end. Finally at 10:30pm we fired the engine up. Of course with no fuel in the injectors it was a tough start but with Fred working the primer pump and me cranking the starter it fired to life. Sounded weird which I realized later was the lack of air cleaner. I backed the car out of the garage and buttoned it down for the night.

I haven't had time to put in the radiator so I can run it up to temp and know for sure the head gasket fixed the problem but I'm pretty confident. If it weren't raining I'd be out there right now. Maybe tomorrow night...


Stacey Beck said...

Something is wrong with my head gasket but I have no clue what. I don't know anything about cars so I appreciate the help. I guess I need to take it somewhere and get it fixed.

Achim said...

When we last left our hero his 1978 Mercedes-Benz 240D was down for the count with a failed head gasket. What to do, what to do? Call out ...