It took me some time to figure this one out, so I wanted to pass along the result. I've had my 300SEL for 3+ years, and I love the car like one of the family. I have the common problem with this engine where I lose (not burn) at least a quart of oil per thousand miles due to leakage at the valve seals. I never saw this as a big issue, since I keep a gallon of oil in the trunk and constantly check the level.

After about 6 months, the engine started missing badly at idle and low speed. I routinely had to start the car twice. After I repaced the plugs and wires, things improved dramatically - smooth idle, one start. Within a few weeks, though, the problems started again. I replaced the distributor and rotor. No improvement.

I mentioned it to a local mechanic, and noticed that when he looked under the hood, he disconnected the #1 plug and nothing changed. He didn't tell me about that, and of course offered to do a tune up for the price of a new car, but I was sure there was more to it than that.

I replaced the plugs again, and the old #1 was completely gunked up; I don't think it was firing all. Again, this bought me a few weeks, and I was back to the bad misfire.

Okay, so I'm dense. After way longer than it should have taken, I realized that the oil coming down from the valve cover into the #1 cylinder was repeatedly fowling that plug.

Now I just replaced the #1 plug, and voila, smooth operation.

Moral of the story, the leaky valve seals was a bigger problem than I thought. They were costing me performance, gas mileage, and maybe a catalytic converter (hope not).

My next job is to replace the valve seals. Anybody know a good source for the spring compression tool? It looks like the tool will cost more than the job.

I have to do the same thing.

http://www.zdmak.com/wbstore/main.asp?LowCt=0&action=cat&cat=MERCEDES%20TOOLS

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Regards

Warren

Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor

Had 1965 220SEb, 1967 230S, 280SE 4.5, 300SE (W126), 420SEL

ENTER > = (HP RPN)

Not part of the in-crowd since 1952.

I too have to do the same job on my M103 soon. I checked your link, but notice it says regarding that spring compressor tool: Applicable: M 114, 115, 116, 117, 123, 130, 180

So the M103 (in the 300E and 300SEL) is not applicable.

Check this thread out: http://www.peachparts.com/shopforum/showthread.php?t=139798&highlight=valve+spring+compressor

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280