It looks like it came from the stop valve, as Brian suggested that it might have. I did see an indication that oil did or had leaked at the valve. As far as NOT being able to blow a rear main seal with that test; I hope you are very right Larry. So far, it doesn't appear to have done any damage, since the oil puddle surprise hasn't happened again since I refilled the crankcase. And yes I was low on oil, because I was going to drive the car until the "low oil level" light came on and at that point measure how many miles I had driven the car. Even with the light on, I still would have had about six quarts of oil in the engine and the dip stick tube WOULD still be submerged in oil at that level and DEFINTELY the oil pump would still have sufficient oil in the crankcase to cause no harm. So, the dip stick having something to do with the oil escaping; I can't make the connection. Now, a bad shut off valve might be another story. Anyway, I intend to see if there is a connection between the no shut off after 100 seconds and my oil consumption. I hope that my no engine shut off condition as a result of the test was an indication that the engine is tight and the oil consumption problem can be attributed to some other mechanism, such as a bad or leaking shut off valve, since the test at a minimum indicated the shut off valve is part of the PCV system, which on other car makes CAN cause excessive oil consumption when the PCV system or PCV valve is malfunctioning. Isn't it on the OM 617 engines that weak engines will shut off quicker if you block air flow?

BenzDiesel

To all:

I had the same issues, major oil consumption- 4 liters/tank full. I pulled the engine , rods 1 and 6 were bent. I honestly feel that the reason the rods bend is that the 3.5 is just a bored and storked 3.0L and that the rod strength or the geometry (rod angle ratio etc) or combination wasn't correct. Bottom line is that teh MBZ engineers screwed up.

I ran a compression check before I tore it apart and the numbers cyl to cyl- there wasn't much different, but #1 was the lowest, but only by 10-15%.

I have seen a lot of engines blow up, hydro lock, racing, thrown rods,head gaskets. etc. I race as a Hobby$$$. Anytime water gets in the cylinder or the psitons smack the head the piston breaks, not the rod. Piston is aluminum and the rod is steel.

RODS-
I purchased new rods from the dealer- $ 250 CDN per ord, they are almost twicwe as thick as the originals. My parts guy at the dealer says this is the 3rd revision of these rods. the new part number is A 603 030 29 20. THEY are much heavier than the old ones, so if you replace them you must replace them as a set and re-balance the einter assembly.

Pistons-
MBZ olny sells standard bore and sleeves. My machinist like to over bore vs. sleeving. He was able to get aftermarket pistons- brand : NURAL part number- 87-743107-40 theis are 0.5mm overbore. They include rings and pins.
Dealer cost for pistons- $3500 no rings, aftermarket $1600 with rings,!! and didn't need sleeves. als

I has had the entire assembly balanced also.

Other stuff- oil pump was $500!!!!!!!!!!!!! YIkes but I put a new one in. All new valves, guides and springs, lifters, camshaft, etc.

I had the IP and ingjectors cleaned and set up at the local Diesel serive center, Bosch authorized center. $500 for all.

I had the trans and torque converter rebuilt also $1500.

I just started it up this morning, motor runs sweet but one of the assescories is making a HORRIBLE squealling sound. I will investigate after the game.

Anyway good luck and happy dieseling!

Steve
Near Toronto, Ontario, Canada
1992 300SD 300,000kMS

good luck

the 3.5 is one engine i wouldnt bore out.

tom w

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

If anyone's still waiting, 9 days later the only oil in #1 is in the piston valve and glow plug recesses. Any oil that could get to the rings is gone. The jury's still out on whether the ring gap is wider than spec or the bent rod messed ring contact geometry.

#2 is at 48mm. Less than 5% of of the piston surface is exposed. Someone asked about the measurement getting bigger rather than smaller. I'm measuring fluid surface from the deck, not the top of the piston.

The 3.5 is close to coming out. Just about everything is off the block. Only the oil filter housing and bell housing bolts remain. The bell housing bolts would be easy to get to from above but there's a brass conduit for the starter cable that's inconveniently in the way. Fortunately I have an impact wrench to remove the IP timer bolt since the head's off. Unfortunately the impact wrench won't budge the crank pulley bolt

Anyone have a starter ring gear lock to lend/rent?

Should a .971 come with a new design vacuum pump? The one on my car is the old style

Sixto
93 300SD

Old style IP vs. New style? My 92 300Sd has the inline IP. SO did my 1987 300SDL.

Sixto
93 300SD

OOPS!! What is the "new" design" vacuum pump?

Steve

I don't know what's different but I hear it includes a bearing that is either less prone to failure or less likely to come apart when it fails.

It's identifiable by having 4 screws into the front cover vs no screws in the previous design.

Sixto
93 300SD

Here is a link you all may find interesting. This person says the MB 6 cylinder diesels bend rods due to the injection pump.

http://www.benzdoc.com/td.htm

I haven't read a post about a 603.96 bending a rod... on any forum. A few have sent a rod through the block.

Interesting through about the pump. Delivery valve sticks open and floods the combustion chamber? Why predominantly in #1 and #6? Wouldn't that blow the tiny return hoses?

Sixto
93 300SD

is needed to replace the rods, the pump, the injectors??? I saw where a pump itself cost over $4,000.00, unless he was talking about a rebuilt or used pump. If it keeps going like it is; somebody is going to write that having a flat tire causes bent rods. Almost all of the other components have been blamed in one way or another and if not directly, then indirectly. I wished he could have elaborated a little more as to how the IP causes bent rods, since he saw this problem from the inside having been a Mercedes Benz dealer mechanic. However, him stating the rod being steel and the piston being aluminum did re-raise a thought in my mind, since logically, an aluminum piston should bend before a steel rod that it is connected to bends without damaging the aluminum piston first before a rod would bend. Which brings me back to the question of could it be the PISTON tilted or bent and the rod is still straight, but just looks bent or is assumed to be bent based on looking at the piston in #1 and #6 cylinders and seeing the piston's tilt toward the front? Also, how can at least five documented 603's on this site alone, have the exact same #1 and #6 pistons be bent, IF there isn't ONE SOURCE and cause of the problem, whatever it is?

BenzDiesel

I think the guy means well but is totally wrong on his claim that the IP can bend rods. No way, no how.

I don't think the IP can bend rods, a lot of fuel to hydrolock, ... exhaust-valve crash bending rod? It would have to happen at the least-clearance moment, when the exhaust is at least partially open, which would bend the crap out of the valve stem and leave an imprint on the piston before bending a rod.

My guess is simply bad rods. Being in the casting/forging business for part of my career, there are a lot of things you can do wrong making an I-beam (or any other cross-section) that can make one side weaker than the other, a post-mortem on the rod would tell a lot. Could even be in the heat-treating.

As far as symmetrical loads on the rod, always the compressive load is symmetrical provided that both journals are centered and there is no significant friction in said bearings, the inertial force on the other hand can cause the bend to favor one side if it is close to the yeild strenght already (a long shot), ... probably the trailing side on the compression stroke as it accellerates laterally, but mostly the bend will compress wherever there is a weakness such as porosity, poor tempering, etc. in the metal.

If this is the case, and the rod is near yield somewhere over its length, eventually the plastic deformation cycles will cause it to weaken further, eventually failing. No cure for this, no prevention. Everything has a maximum life and usually the harder it's run the faster it'll fail.

Why it manifests itself more on the 3.5 is anyone's guess, I'd say since the rods are unique to the engine, it probably has nothing to do with rod integrity in the other engines of the same family or even the increased power of the engine. Same metal with different flow in a die can create totally different finished product. Proper / upgraded replacement rods will probably out-last the block.

Bad rods, nothing more, and it likely was corrected later in production or in replacement parts.

Just my opinion.

__________________

Gone to the dark side

- Jeff

i did a search on net as to where one could buy the nural piston and came up blank, do you think you could post the source of your pistons?
thanks larry perkins lou ky

While it's certainly possible that certain rods are defective from the factory, if they are forged (likely), the chances of them bending in operation due to running over the design loads are minimal. In any other engine, you can run the rods just about forever and never exceed a design load.

A far more likely scenario is high cycle fatigue. It's related to loading, however, is governed by the on and off cycling of the load. The distribution of failure in high cycle fatigue is huge. One rod may fail at 4,000 hours. The next rod in the batch may fail at 40,000 hours. It's not easy to define high cycle fatigue life. Jet engines suffer from this malady and all of the rotating parts must be scrapped before the very first one of the group suffers from high cycle fatigue.