Head gasket M103 300SE
 

It's true, a cheap Benz is going to cost you. Anyways, It looks like I have to replace the head gasket of my '90 300SE. I'm losing a lot of oil and the coolant is black with motor oil. Just did a coolant flush, less than 400 miles and it seems to be worse than prior to the flush. There was some oil in the coolant before, but very little, now it's black, it's milky around the cap and the car runs hotter as well. I think bad motor mounts have speeded things up a bit.

I've done the head gasket on my Volvo 780 with the B230T and it was a fairly easy job, would the M103 compare? If I do it myself I'm hoping I can leave the exhaust manifold attached to the head and only take the intake off.

I'm doing some research at the moment, any pointers for someone who will undertake this for the first time?

It's straightforward. You can lift the head with manifolds attached but they'll have to come off for a shop to check the valves (guides, seats, etc.). I think you can lift the head leaving the manifolds in the engine bay. The stub hose between the water pump and head ranks among the top 10 MB bonehead design moves. The horseshoe gasket between the front cover and head might qualify.

Sixto
98 E320s sedan and wagon

I will replace all the coolant hoses when I'm at it. Should I replace the water pump, it's original and I'm almost at 90K miles?

I wouldn't replace it because of 90K miles. I'd replace it because the head's off. Mind how the belt tensioner goes together. Intuition and logic don't help :p

Sixto
98 E320s sedan and wagon

be aware the chain tensioner has to be reset before installing. otherwise, the chain will break.

having done both volvo and mb for 25 yrs. or so, there's alot more steps with a m103 compared to a b230ft. i can have those heads off in 90 min, mb takes longer. go slow, read alot and take pictures. good luck, chuck.

How is that accomplished? I'm not doing the head gasket but a reseal of an engine (head job was done before I bought it) and of course that included pulling the tensioner out. Want to make sure I do it right putting it back together.

Curious about this as well, I have not read anything about it.

This is what I will be doing:

Fresh head gasket. (Mercedes)
New coolant hoses. (Mercedes)
New motor mounts (Mercedes)
New idler arm bushing (Lemforder)
New water pump (Graf ?)
Fresh seals and gaskets
Oil change and coolant flush

read this-

Mercedes-Benz W124 Timing Chain Tensioner Replacement | 1986-1995 E-Class | Pelican Parts DIY Maintenance Article

good luck, chuck.

Thanks!

Leave the exhaust manifolds attached to the head, just detach the egr pipe. Unbolt the intake but leave it in the car. Don't forget the two bolts in the brackets under the intake as well as the egr pipe mount in the rear by the coolant nipple. With all of those loose you can just pull the intake away from the head enough to pull the head without having to disassemble all the crap on the manifold.
Try not to break the plastic chain guide rail when you lift the head (or when you pull the pin for that matter). It wants to break but if you remain conscious of it while lifting you can avoid it.
Don't go crazy with sealer on the worm seal for the timing cover. Just a small dab in the corners. The more goop you use on it, the quicker it will leak.
If the head doesn't have to be machined, don't disassemble the cam and rocker towers. Those threads are iffy at best, and best left alone if just doing a quick gasket swap.
New head bolts are worth the money and cam gear bolts are mandatory. Also when I do these engines I use some of the black M/B sealer on the perimeter of the gasket on both sides. It adds years to the reoccurrence of external leaking.

Do a compression test before pulling it apart to identify problems.

Replace the valve seals. Intake and exhaust seals are different, sort them and show the machine shop if going that route.

Stuff the timing chain cavity with clean rags to prevent uninvited drop-ins.

Using a new OEM hose...put a new hose on the water pump between the water pump and the head before re-installing the head. Put a note in a visible place to do this, you will not be happy if you forget!

And, turn off your phone, radio and TV, take a break and then have a helper watch/monitor the torquing sequence. Using paint mark the 12 o'clock position of each head bolt before starting the 1/4 turn angle torquing procedure.

Good luck!!!

Went to the JY to take a M103 apart to see how it all works before I replace the head gasket next week. I'm confident I can tackle the job, if I don't run into trouble with rusted bolts and nuts it's pretty straight forward.

One thing that I found and I experienced this with two separate engines in the yard was that the head bolts were not as tied as expected. With a 2 foot breaker bar they came loose without any resistance. Both were fairly low mileage cars.

Another thing I was thinking of doing was replacing the stem seals and guides, the car isn't burning any oil that I know of, but because the engine open, why not? Is this something an amateur mechanic can do or should I leave this to a professional? 90K miles.

And do I have to drain the oil before taking the head off?

You can change seals easily. Use MB brand seals. Valve guides are machined to fit and IIRC require heating the head locally for proper fit. Not a typical DIY job.

Sixto
98 E320s sedan and wagon

Thanks, good to know.

No need to drain oil first.

Take head to machine shop if possible to have it checked for straightness and planed if necessary. They can also vacuum test the valves if you leave it assembled to confirm no leaking valves.