PeachParts Mercedes-Benz Forum - Rod Bender True Stories

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Hmmm, try fumigating a junker with oil mist and see if you can get detonation. People talk about run aways, I wonder if they have rod bending... I've only heard of detonation with propane.

I don't really know much about these engines, but when you repair an engine with a bent rod, do you just replace the rods with bigger (stronger) rods? Does the head gasket get replaced? Would the same leak develop again? Because if the leak is still present and the only thing different is bigger rods, you'd have knocking or other similar symptom...you'd still be pre-detonating.

I have been pondering an abnormal combustion event as the cause myself but I was thinking it might be from steam.

I don't have enough knowledge about the combustion process and the potential pressure from an event as you describe to evaluate it.

It seems worth exploring.

Tom W

I have proposed a test of the theory using a friend's a W126 with a 3.5 liter 603. We would bore a hole in the air pipe and place a fuel injector there. Then rig a pump and a small auxillary tank of motor oil. Then with hot oil in the auxillary tank he would run the car flat out at full throttle full speed on the highway and I would switch on the injector. He declined to do participate in the test.

Engine #235 started to run away at idle when it was fully warmed up, and leaking oil. That is why I think it is getting oil mist. Liquid oil getting into the cylinder would not ignite and burn enough to do anything.

More random guesses.

The FSM touches the rod with his noodly appendage.

Quote:

Originally Posted by babymog (Post 1808386)

I pulled the head from a junked '87 SDL today, 196,000miles, saw some interesting things.

The head gasket is of the original design, likely original, #14 head. No evidence on any of the cylinder seals or the passeges of any leaks, pretty much a perfect seal. Also no cracking. In the spare parts rack.

The turbo was a different story. Full of sludge, so was the intake and crossover. The wastegate was not hooked to the vacuum diaphragm, so it was left to be open all of the time, no boost.

Jeff,

Fundamental flaw in your theory: The 1986/87 300SDL has a pressure type wastegate. With the hose disconnected, it runs with the wastegate stuck closed, and overboost is likely. Could be that engine ran with 17psi of boost most of the time. The vacuum wastegates did not come out until 1990.

Also - make sure you are not confusing the wastegate hose, with the ARV vacuum hose that goes from under the airbox on the SDL, to the front of the turbo. Totally different functions there. The ARV should be disabled, btw, by disconnecting it.

:stuart:

Let's shoot down this "oil in the intake" theory right now. The presence of oil in the intake is NOT a problem. A car that is running normally may have this. It DOES NOT necessarily mean the turbo seals are shot. Here's a factory PDF alluding to this, and although it only mentions .96x engines, the same would apply to the .97x as well:

http://www.w124performance.com/docs/mb/OM60X/oil_in_intake.pdf

:nuke:

Quote:

Originally Posted by jmfitzger (Post 1810128)

Today we tested engine #235. Removed #1 injector, removed the air pipe and the blow-by tube. It was down 5 quarts of oil so we filled it. We fired it up and let it idle. Every time the piston stroked up, compression and exhaust both, oil sprayed out of the pre-chamber throughthe injector bore. We let it idle for about 5 minutes. There was oil all over the shop and the shop owner. We then shut it down and took it apart.

The intake manifold was oiled everywhere, wet but not soaked. The inlet tube going from the air filter housing to the turbo was wet from the cam cover vent tube inlet the turbo compressor inlet. The exhaust manifold was wet with oil inside.

We removed the head and found the gasket blown out at the oil channel adjacent to #1 cylinder. (now, AKA the aorta on 603 engines) The seal ring was broken and the ring was bend outward on both sides of the break. the gasket material was burned or melted or otherwise alblated all the way acros the oil channel and through to the chain tower. So the gasket was breached all the way across the oil channel and into the chain tower.

This is not anything unusual... the head gasket problem affects all OM602/603 turbo engines. My 602 had the identical failure two months ago (photos are at this link). I managed to catch mine before it blew the stainless ring around the top of the cylinder bore though.

At any rate, it's not valid to pin rod bending on this failure, because otherwise there would be hundreds of 602's with bent rods, and there aren't any. Note that the latest cylinder 603 head casting (#22) has a redesigned oil channel which will greatly reduce, or eliminate, the chance of this gasket failure re-occuring. Photo is below. I believe the latest 602 casting has the same update to the forward oil channel.

http://www.w124performance.com/image...eads-front.jpg

Quote:

Originally Posted by t walgamuth (Post 1809525)

The older engine does not have the block flex that the 3.5 has.

I agree that the cracked heads on the 3.0 did not come from hydrolock.

The hydrolock theory has the same problem as the oil channel (or turbo seal) theory. If this were true, the 2.5L and 3.0L engines would also be bending rods. They ain't. So we're back to the 3.5L rods being of a weak design, or unable to deal with the enlarged block, or something along those lines. The fact still remains that we have yet to see a proven case where a fresh 3.5L rebuild with the new/updated rods has re-bent the new rods.

:zorro:

I might not have put this clearly enough.

The wastegate was disconnected, the clip came off of the wastegate actuator arm, let the wastegate flap in the breeze, not the vacuum line. No boost.

I do agree it's difficult to blame the head gasket seal if it didn't manifest itself on the 2.5 and 3.0 engines.

Quote:

Originally Posted by gsxr (Post 1811078)

Seems like it would then occur often on the '87 603 and 602 since they had bigger problems with the head gasket. Further, it would then stand to reason that all failed rod engines would have head gasket failures, which has not been observed at this point.

Under full throttle, a higher rpms, the amount of air flowing through the engine is so high that this oil mist is probably not enough for a flammable mixture. The conditions have to be just right to actually fire. but if there is ALOT of oil mist, then yea, I believe it.

Someone take an oil crappy diesel and shoot some diesel mist into the intake and see what happens

The bulletin says engines built after 3-31-94 do not have this problem.

So are there any 3.5 liter 603s built after this date that have gotten the bent rods. MB is still remanufacturing 603 3.5 liter engines. Do any of the engines manufactured after 3-31-94 have rod bending. Are there 603 3.5 liter engines with bent rods that do not have head leaks at the #1 cyclinder.