Timing Chain Replacement Advice - PeachParts Mercedes-Benz Forum

stephenson · #1 09-11-2002, 11:51 AM

Induction system is still off on my 1991 350 SDL - getting incredible amounts of coked on oil removed (machine shop said they might not even be able to get it off!). 20% blockage at the turbo to induction crossover pipe "flex" interface. Chunks the size of quarters fall off! (Have repaired (!) EGR and will likely run crankcase vent line from valve cover to outside of car (where is the best place to let it vent?)

Question is: While I have valve cover off, what else should I do?

Initial impression is to simply replace all glow plugs (they are original and it does have characteristics of failure).

How about the chain? Looks straightforward, but would really appreciate some advice on replacing it, whether or not to replace the guide rails, and what about the tensioner?

Car was running extremely well so have no other failure indications - well, other than an occasional pause in power at high speeds as the chunks of coked oil fell off the sides of the induction system and were ingested into the cylinder and burned (aaaccck). Is it possible this is directly related to the 3.5L diesel engine failures?

engatwork · #2 09-11-2002, 12:43 PM

Personally, I would leave the crankcase vent system along and just try to "experiment" with the egr system.

stephenson · #3 09-11-2002, 01:36 PM

engatwork,

Are the unwanted (other than oily deposits under car and pan) of venting?

engatwork · #4 09-11-2002, 08:02 PM

I do not understand your question. The majority of the build up is from the egr. If the crankcase venting system is working properly then most of the oil, in liquid form, will go back to the oil sump and the vapors will get burned.

stephenson · #5 09-11-2002, 08:10 PM

engatwork,

Sorry ... probably wasn't clear. I was asking if there were any other side effects of venting to the bottom of the car other than oily residue.

I understand your point on the EGR, but it seems like there is simply too much stuff to be egr only ... perhaps it is the location of the egr - and the interaction with the fumes?

I am probably gushing, but I was just amazed at the quantity of stuff ... there is on the order of a pound of it I'll bet ... what SHOULD it look like in a perfect world? (I would guess it would be oily with a bit of sticky old oil?)

Any recommendations on what else to replace based on the mileage?

Thanks for your comments!

engatwork · #6 09-11-2002, 08:26 PM

You did not mention mileage but if it is over 200k I would just go ahead and change the chain. I would replace the gp's just because they are a pia to get to with everything in place. Again, I would make sure the line coming off the top of the cam cover is put back to it's original condition. I'm pretty sure the majority of the stuff you are seeing in the intake is coming from the egr. Make sure the system that seperates the fumes from the liquid oil in the intake is working properly (on the "engine vent" system). The W123 cars have what I call a "cyclone seperator". It creates a spinning motion to throw the liquid to the outer edge where it collects on the side of the chamber and drains back into the oil pan while the fumes get burned. I would be surprised if the system on the 350 is designed differently. You do not want that vent venting to atmosphere - it is going to create a big mess along with increased oil consumption.
OT - the sale of big over the road trucks (2002 model year) went through the roof this year because next year the epa is requiring them to be sold with an egr system and the trucking industry went on a buying spree. The trucking companies are very concerned because of the increased maintenance cost and reduced economy. They will be cleaning out those intakes just like you are having to do now.

GregS · #7 09-12-2002, 05:49 PM

I don't claim to be an expert on the topic of the motor in the 350sdl, but yes, there has been speculation that ingesting chunks of buildup from the intake manifold is what takes out these engines. I have heard of the same thing happening to a VW turbodiesel too. If you plan on keeping the car a long time, you might want to invest in a CCV scrubber. These components filter out the oil mist in the vapor, and you can install them so they drain the oil back into the oil pan. A company called Racor (Raccor, spelling?) sells them for around $185. Its true that Mercedes installed an oil seperator on their diesels, but just look at the intake of a w123 to see how well the work. There is oil all over the place! These Racor units will really scrub all the oil out of the crankcase vented gases and return oil-free air back into your intake.

Greg
'84 300D, 166k