I've gotten so much out of this forum just lurking, I thought I'd share my successful experience with a valve job on my 1986 300E for others to benefit. I pulled the head myself, and had the valves done by a local independent.

First the problem. I bought a 1986 300E for $3,500 with approximately 150,000 miles (odometer stuck at 128,000 but service records show 121,000 in mid-2000) with the caveat that it needed work to pass smog. Seller was vague as to what work was needed, but he said about $1,500 worth. The car performed well in a test drive. Off-idle performance was fantastic, a smooth and strong runner, but idle was very, very lumpy. Buying the car out of the guy's carport with other potential buyers ringing his phone off the hook precluded anything more than a thorough test drive, although I would've liked to check the compression.

Long story short, it wasn't just plugs or injectors or OVP or something easy like that. Despite the fact that the car ran strong and had no contamination of oil or coolant, I found I had low compression on neighboring cylinders 2 and 3. Compression on the two low cylinders was 90 and 100, all others were around 195. I guessed head gasket, but was puzzled by the fact that the oil and coolant hadn't mixed. I paid an independent $190 to check it out and his conclusion (after blowing smoke into cylinders and chasing it with compressed air to see where it leaked out) was that the exhaust valves were leaking (leakdown 100%) on both of those cylinders, and the car needed a valve job. He said about $2,500 ought to do it, but that it might be more or less once the head was off and we found out what was needed.

Ultimately, I pulled the head myself, to keep the total repair cost down, and ended up taking head back to the same independent to actually do the valves (this shop is one of those few who like to do valves by hand in-house).

Here are my experiences with the cylinder head R&R on this 103 motor:

Overall, with the factory manual ($70 from books4cars.com), the job was really pretty simple. If you've done cylinder heads before, you can do this one yourself.

Leave the intake manifold in the car, despite what the factory manual says. It looked easier that way, several posters here said it was easier, and when I was done... I am sure that it was.

You will need a 14mm and a 17mm hex socket to get the chain tensioner out. You will find you cannot buy anything larger than 10mm hex sockets even at a well stocked tool shop. I found Snap-on to be the only supplier of hex sockets over 10mm, and bought a whole set for $180. Even that set did not include the 17mm size, but I found a 17mm wrench (not socket) at Post Tool.

The head bolts themselves are 12 point hex (I forget the exact size), not Torx like they appear, nor 6 point hex like the Snap-on set you just bought.

The camshaft gear bolts *are* Torx, the only ones I think in the whole car. Just a little MB joke, I think.

I did not find any of the supposedly tricky procedures, like pulling the guide rail pin or taking the chain tensioner apart after removal and reassembling it in situ (so it can retension) to be very difficult. I was able to pull the guide rail pin with a 6mm (or was it 8mm?) screw through a socket and a few nuts and washers. No trouble. You definitely don't need the fancy tool from MB.

I did, however, break off the top of the timing chain guide rail as I singlehandedly removed the head despite the greatest of care. A mishap with the little hoist I was using, I think. I did not see it actually happen. Big mistake.

If you break off a timing chain rail, you're in for the treat of tearing down the whole *front* of the motor (removing radiator, fan clutch, alternator, tandem pump, and a bunch more) to get the timing cover off to repace the rails. Doing that work requires putting some torque on the crankshaft pulley, and for that you might need a flywheel lock. The special "flywheel lock" is $120 from Mercedes. That makes it worth some improvising. There isn't much room to improvise, though, and when I used a bit of angle iron wedged against the tranny case opening, it worked, but I busted a little aluminum half moon out of the corner of the case opening. Darn. The whole "R&R timing cover to replace the busted guide rail" detour was about a whole day lost. That said, at least I have nice new guide rails, and I cleaned everything up real nice and apparently fixed an old timing cover oil leak. Other than the flywheel lock which would've been nice to have, the timing cover/guide rail job did not require any special tools, just time. I did not replace the timing chain itself, although I know that whether or not to do so is a divisive issue hotly debated on this forum.

The car went all back together real easy, and now runs and idles wonderfully. It aced its smog retest after the repair.

The only post-repair surprise was that in the course of doing the timing cover I cleaned all the bracketry and such with Foamy-Brite to get rid of the deposits from the earlier leak, and in doing so I must've accidentally cleaned all the grease out of the fan pulley bearing. After just a day or two it went squeal-squeal, bang, bang, bang and removing the bracket revealed the bearing had completly disintegrated and was letting the fan pulley wobble. A new bracket was $169.

Kudos to All Mercedes in Oakland, CA (www.allmercedes.com) and their helpful parts folks.

The valve job itself was about $660 at Germany's Best in Oakland, where it got a really meticulous hand done job, but I also had to cover the machine work they sent out (straightening head $105, resurfacing $65) so that total was more like $838.

I took the job to the independent because they were already familiar with the odd symptoms the car had and I wanted their take on whether the now-removed head was really the cause, or if it might've been some other problem. If I had it to do again, I might've just taken the head to a machine shop for faster turnaround and lower cost.

As the valve job was taking a while (more than a week), I considered pulling the job from the independent and taking it to a machine shop so I could get the car back together. I asked All Mercedes for a machine shop recommendation. They unconditionally recommended Star Machine in Emeryville, CA (right by my office), a specialty shop that only does Mercedes heads. I talked to Paul at Star Machine 510-547-1171 and he said their usual rate was $324 for a 103 head, and their turnaround was 24 hours. I don't know if the straightening my head turned out to need would have been over and above that $324 number. The independent finished in time, but I wish I'd known about Star Machine before I made my other commitment.

How'd the cylinders look? Could you still see the cross hatching?

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Jim

The big 14 and 17mm hex sockets that you needed are available at your local Autozone store in a set made by OEM (that is the brand name) and cost about $12 the whole set. Actually the set includes a 12, 14 and 17mm hex sockets. Part # 25417. You are right, they are hard to find. Every person who works on his Benz should have this set in his toolbox, as MB uses them quite extensively, (rear differential mounts for example).

How did your hand feel after pushing in the tensioner cap screw with the spring behind it while simultaneously trying to screw it in? And how many tries before you started to curse like a drunken sailor?

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-Paul-
'01 E430, Sport 72,000 mi
'98 C280, 126,500 mi

Following up...

The crosshatching on the cylinder walls was still very clear. I wasn't up to doing anything with the bottom end, so all I did was rotate the motor 120 degrees at a time (so that two pistons at a time would be at TDC) and carefully cleaned the piston tops with a wire brush while protecting the other cylinders by stuffing them with clean rags. They all cleaned up shiny bright, so you could make out the tiniest lettering still forged into the piston tops. The only scary bit was number 5 which cleaned up nice and bright but had a few dozen really tiny pits, like a woodpecker had been pecking on it. At some point in the past, a bit of carbon or who-knows-what must've rattled around in there before being pulverized. Since each pit had a microscopically raised edge, and thus roughed up the piston top, I knocked the peaks off with a bit of sandpaper so that despite the pits the surface ended up smooth to the touch.

I'll remember the tip about AutoZone as a source for the big hex sockets, but I don't think I have any in my immediate area. Mostly I have Kragen and Napa Auto. And of course now I also have a set of Snap-on sockets.

Yes, now I recall about how hard it was to get the chain tensioner cap on against the spring tension. Ultimately, I think it was a two handed job kind of holding it by the edges and pushing with my thumbs, with my fingertips over the edge to center the spring, and rotating it that first half-turn into place by rotating my hands like I was turning a steering wheel. I did not need to curse like a sailor, because I had already gotten that out of my system when I saw I had broken the timing chain rail. One odd thing stands out, though. When I pushed the tensioner plunger back into the just-reinstalled outer sleeve, I expected the little little ring washer on the trailing edge of the plunger to start back into the outer part and ratchet in a bit. It never did. The ring just hung up at the stairstep edge of the outer housing, even when I pushed pretty hard on the plunger. With all the tension on that spring, I could see that the timing chain was in fact being tensioned, but I thought it was odd that the plunger didn't seem to start ratcheting right away. I think it must've ratched by now. Anyway I don't hear any chain noise.

I noticed you remarked to leave intake manifold in engine compartment although manual advises otherwise. I plan to replace head gasket on 96 C280 104.941 engine and manual also adivses to remove head with both manifolds attached. Did you also unbolt exhaust manifold before removing head?

Hilton,
Unbolt the exh at the "down pipes". You really can't get to the exhaust manifold/head fasteners with the head on the engine. I unbolted the intake manifold and pulled it out separately. You will want to get the egr pipe out where you can clean it real good. If you look at the vacuum piping underneath the intake manifold you will see one that comes down and attaches underneath the water pump area. Unhook it at the under water pump area end. Do a search - I just did this on the 104 engine not too long ago.

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Jim

Jim,

Thanks for the info on manifolds and I will do the search. Is the 104 engine manual (104.9xx) that is available from MBUSA applicable to the 104.941 except for minor subtleties such as the fan pulley removal locking method to be adequate for guidance in the placement of the head gasket? I know I can order microfiche, but the descriptions are not sufficiently definitive to be sure what to order.

Hilton

I don't know about the manual Hilton. Don't recall having to pull it out when I did mine except for the various torques which I got from the Technibooks manual.

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Jim

What is a "Technibooks manual"? Is this available to general public?

Hilton

http://www.mainlineauto.com.au/support/techpublications.htm#MERCEDES

It is pretty much the same thing as a Haynes manual. Pretty general but does provide some good information. I have the CD rom for the car but hardly ever use it.

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Jim

Thanks again for the info. I am slowly accumalating specs and technical info on 104.941engine/202 chassis.

Hilton

Hilton,

Jim gives good advice on the 104 head removal. It is a different animal than the 103. I believe on the 104, however, you will be better served to pull the head with the intake manifold attached. If you have an overhead crane this will be easy, if not, you need a friend that's willing to get dirty.

The 103 is DEFINITELY easier if the intake is left in place.

I don't remember the tensioner being any problem at all. Simply push the plunger all the way through then start it through again, it is a ratcheting mechanism. This holds true for both engines.

Good luck,

Although others followed up on Hilton's question about whether he should remove the exhaust manifold on his 104 motor (different animal), I thought I would reply with what I actually did on my 103 motor. I completely removed both exhaust manifolds before I pulled the head. Probably I could have just disconnected the "down pipe" bolts and removed the manifold on the bench instead of in the car, but I think that taking the exhaust manifolds off makes the head easier to handle both for removal and reinstallation. For example, with the exhaust manifolds removed as I lowered the head back on, I did not have to worry about getting the down pipe bolts to align while I was worried about all the other alignments. Getting the exhaust manifolds back on does take a firm hand in flexing things to get it all to line back up, but I don't remember it being all that terrible.