Why is my 300e EATING cam's
 

Hi all,

I have a 1987 300e with somewhere around 150,000 miles. True mileage unknown due to notoriously bad odometer broken when I got car.

3 years ago I had a severe oil consumption problem and this forum led me to replace the valve stem seals. When I removed the rockers to replace the seals I discovered that some cam lobes and their corresponding rocker arms were worn to nubs. I replaced the seals (which solved my oil consumption problem - now 1 qt per 1000 miles) and the cam/rockers at the same time. The cam that came out of the car was stamped with number 22. I replaced the cam with a 22 from a used car that showed NO signs of wear. I even mic'd the journals and they were all within a thousandth of each other.

Now 21,000 miles later I heard a ticking from under the valve cover and I have at least 1 lobe/rocker almost gone. I use Mobil 1 10W-40, the oil tree is providing LOTS of oil, my oil pressue is 3 bar at anything over 1000 rpm and perhaps .9 to 1.0 bar at idle.

I'm looking for a cam right now and trying to find a 49 cam (assuming that will fit). But I'd really like to know why I'm eating cam's.

I rebuilt front and rear suspensions, the A/C system, and a multitude of other things. We really love this car, but if I'm going to be replacing cam's every 20 thousand miles I'm selling!

Any ideas?

Thanks,

Is it always the same lobe that gets worn out?

Something must be wrong with that motor.....my M103 has 138k on it and the cams look like new.....I use a 5w40 synthetic oil.

take a pic

Yes, there is something wrong with the motor. I just don't know if #22 cam's are made with softer steel and wear out at some point (I don't know how many miles were on the used cam that I got), or if it's Mobil 1 oil or something else. I see that #42 cam's were tin coated and #49 cam's are chilled cast iron. I'm guessing that MB might have detected a defective manufacturing process and changed along the way to extend the life of the cam's.

My second cam wore out different lobes than the first cam, so I'm guessing that it's not my oil tree.

Thanks,

Up to 89 the cams were not as durable. With the chilled cast iron cam longevity increased considerably. The kicker is that the chilled cast cams have to be used with the newer style rocker arms. They aren't compatible with the older rocker arms. You'll also need the later style distributor rotor adaptor, its slightly different between the two style cams.

To answer your original question, you are losing lobes b/c there isn't enough zinc additive in the oil you are using. Just because an oil has a premium synthetic base doesn't mean the additive package isn't critical.:rolleyes:

Damn, I'd say you have a problem there. Maybe a lifter issue.

Wow.... I was gonna guess that it was a compatibility issue between the rockers and cams, but I had no idea it was so serious or that the metallurgy had changed so much.

Boy, I'm glad my motor's a '90 because I've been using Mobil-1 10W-40 for at least a year...... My cam looks great..... BUT - Is there something in there that needs the additives lacking in this oil? Am I doomed?

That's a LOT of metal you've got in your crank case now.... I would recommend putting a magnetic trap somewhere in there after you get this fixed. I dunno, do they make magnetic oil drain plugs for this car?

Probably want so drain the oil and flush the snot out of the motor while you're at it......

Doomed? Nah. The later models are more durable. As long as you do regular oil chages you won't see any appreciable wear on the cam. The softer metals used in the older cams (pre '90) really benefit from a high zinc additive in the oil. At the shop we use BG's MOA in all non synthetic oil changes.

Thanks!

Looked at your photo. Holy ****!

That was after 21k miles?????? :eek: :eek: :eek: :eek: :eek:

What oil do u recommend?

Doesn't diesel oil have higher Zinc in it? If so, thats what I have been using in my M103...but its a 1990 model so its a chilled cast iron unit.....thankfully.

Have you considered that you may have a problem with the cam journals in the head...
Wear, runout or alignment can cause excessive wear on one or more cam lobes.

The rocker arms are the most common problem. The newer version has a MUCH harder wear area that is welded to the rocker arm. USE that version with a hardened cam from a 1990 OR later M103 engine!

IF you are using used parts MAKE sure to put rocker arms against the same cam lobe they have been riding on.