M116 Eats Cams??? - PeachParts Mercedes-Benz Forum

Strife · #1 07-13-2009, 02:18 PM

When I purchased my 380SL at 95K miles, it made a terrible valvetrain noise and I purchased the car with repairing this priced in. As I thought, the rearmost lobe on the RH side was eaten, and the cam follower was severely grooved. This might have had something to do with the oiling tube so loose as to be easy to actually lift off of the cam towers.

I replaced the cam with a new aftermarket cam, and all new rockers. The oiling tubes were cleaned to surgical standards and fitted with new plastic fittings. Naturally, I used break-in lube. To be on the safe side I also replaced the hydraulic compensator for that valve with a new one. The shim looked a bit "polished", but still OK.

All seemed well on the 380SL,for 25K miles.

Before I owned it, this was obviously not an example of a "well-maintained" engine. When I change the oil every 3K miles (religiously), the oil looks old and the car may burn 1 quart every 1-1.5K miles, not great, but not unreasonable at 130K miles. There is some blow-by. My 560SL leaks, not burns, and at 3K oil changes (on a 108K engine), the oil looks almost as good as when it went in.

Anyway, all seemed well on the 380SL.for 25K miles, although there were a few surprises along the way - but nothing from the RH head. Until now. I took the RH side apart, and basically, the same thing happened again, although I obviously caught it much sooner. The cam looks only a little "gouged" on the lobe tip, and the follower is not nearly as bad (but still unacceptable).

I really don't want to replace the cam again. I actually would be willing to do it if I found a good used one (if possible) but I would worry about pushing my luck with the cam tower bolts, which are of course really head bolts.

I have, however, planned on cleaning the oil tube (I do NOT think it is plugged), putting new fittings on, and replacing the rocker. I have the "normal" and next biggest shim size shims that I can install.

Questions:

1. Why does this always seem to happen on the 116? On the RH, and on the last cam lobe???
2. What are the ramifications of putting in the new rocker and the thicker shim? (5.1 to 5.45mm). Any guesses on how long this will last? 10 miles? 100? 1000? 10000? 100000? (ha ha).

Thanks

tinypanzer · #2 07-14-2009, 06:20 PM

What kind of oil are you using?

I read in another thread that the older motors used a different cam metallurgy and required zinc additive in the oil, which is being used less and less these days.

But that was on the M103, somebody else will have to tell you if this applies to your car or not.

Strife · #3 07-15-2009, 02:45 AM

You know, I've been thinking about this too (ZDDP). I don't know if newer engines have better metal, or if they are designed with lower leverage pressures (there must be a mechanical engineering term for this). It's my understanding that without these additives, it's harder to form a consistent oil film under high pressures. Pushrod engines without roller rockers and early OHC engines are very demanding in this area.

Supposedly, there are additives that contain twice as much ZDDP at the same price as the GM additive, but with 9 quarts of oil to change every 3000 miles, this is going to get expensive if it's needed (+20 an oil change).

CWW · #4 07-15-2009, 01:11 PM

You guys with the older motors really ought to be using a higher viscosity synthetic, the film strength is multiples of dino oil, and it doesn't shear down nearly as quickly.

And for peace of mind add a bottle of Ford or GM "Engine Assembly Oil", which has a high enough zinc content to more than offset the new EPA regs' recent reduction in zinc in motor oils.

The old wives' tale about switching to synthetic in a motor that is used to dino oil causing all sorts of oil leaks isn't something I particularly buy into. Yes, it may remove crud that was plugging areas around a bad seal, thus allowing a leak, but that meant the seal really needed to be replaced anyway. So what's the difference. Much better protection for the motor.

waybomb · #5 07-15-2009, 01:58 PM

My boat has three big blocks. I still run solid flat tappet cams.

A few years ago, about 15 hours after changing the oil (5 gallons per engine), I wiped all three cams within an hour of each other. So badly that I had to take the lifters out the wrong way in some positions.

Made no sense to me at the time. Lo and behold, I discovered about half of the zddp was removed from my "racing oil" because of EPA regs for catalytic converter fouling caused by zddp.

So now I use Rotella T and a quart of GM EOS in each engine.

Sure would like to find something cheaper than the GM EOS. I bought a few cases of the older stuff on ebay. The stealership wants about 15 bucks a pint for the new stuff.

Someday I'll build the engines with roller cams but then I'll have to change cam profiles, meaning a change in horsepower. And if I do that, I may as well go 1300 hp each with new #6 drives. My wallet won't like that....

G-Benz · #6 07-15-2009, 02:32 PM

The "zinc content in the oil" argument sounds compelling, but in Strife's initial post, it seems that the problem is with one cam lobe on the right side, not every lobe on both cams.

I would think excessive wear on one lobe would indicate an isolated problem with that area of the valvetrain, not something a change in oil formulation would cure.