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Old 08-02-2002, 03:19 PM
marinmbfan marinmbfan is offline
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Join Date: Aug 2002
Posts: 52
Sharing experience with cylinder head on 103 motor (1986 300e)

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, 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 ( 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.
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