broken diesel, owner needs help

[MS Fowler]

A cousin has a Mercedes diesel that just died. He wasn't able to give me much information, and other than W123 and W126 chasis< I do not know much.
I'll post what information I have----
1990 300D 2.5 liter turbo
While driving up the interstate, he noticed a large puff of black smoke ( first time he ever saw more than wisp) and then lost power. Quit and would not restart. Had it towed to his mechanic and was told, " its the oil pump, you need a new engine". Had it towed home and his neighbor got it running, roughly, but it wouldn't keep running. For some reason, the neighbor thinks it needs only a crankshaft and bearings. I don't know why as my cousin said there was no abnormal noise.
I hope to go visit, and check it out myself, but any guidance you all can provide would be appreciated. Is this a chasis?
Is this a "normal" failure mode for thse engines?
Thanks all.

[Jim H]

This is not a normal failure mode. Normal failure is usually compression that decreases over time until it's so low that it won't start.

His mechanic, apparently without doing any testing, says it the oil pump, and he needs a new engine? Did the oil pressure drop before it lost power? Did the oil level light come on? If not, why suspect the oil pump? Time for a new mechanic?

The neighbor got it running, but couldn't keep it running, so he thinks it needs "ONLY" a CRANKSHAFT and BEARINGS? Why would he think that?

Loss of power is usually because of a loss of fuel. If it will start, but not keep running, it's probably because it's not getting enough fuel, or not getting the fuel at the right time.

Loss of oil pressure is usually accompanied by an engine that stops turning, and will not turn, or if it does turn, it will knock very loud.

There is not a lot of information to work with yet, we would need to know more.

How many miles on this engine?
Were the fuel filters ever changed?
What work, if any, was done before this incident?
A complete description of it 'lost power' including what the gauges were reading, how long the engine ran after the smoke, etc.

I'm sure we'll all try our best to help.

Best Regards,
Jim

[rg2098]

A large puff of black smoke would also lead me to believe its fuel related issue.

[coachgeo]

hmmmmmm.... loss of power all the sudden. sounds familure in a way. Is there a Cat converter or some simular thingy in the exhaust. If so it may be plugged and causeing backpressure.

[MS Fowler]

I had a lot of the same questions--what would lead the mechanic to question oil pump? I don't know, I was just relating what I've been told. So far, its all hearsay.
I will get some more information when I eyeball it.
The puff of black smoke does sound like unburnt fuel. How solid are the timing chains in these engines--do they jump time?
Thats for the answers, I will provide more information as I get it.

[Jim H]

Yes, sounds like you weren't given a lot of info to start with.

From what I know, timing chains are quite solid. They will wear (not really stretch) until performance drops off, but seem to rarely break.

I've heard of the breaking, but never heard of one jumping.

Best Regards,
Jim

[Eric Eliel]

It won't run PERIOD with a broken timing chain (let alone start). When it did start, what did the oil pressure read? If it has good oil pressure, it doesn't need an oil pump.

sounds fuel related too

[Hatterasguy]

Actually this is not a common problem but it has happend before. Their are a few owners of these cars that have posted here with bad oil pumps. I guess the chain was some what week on those. Btw the timing chain has nothing to do with the chain that drives the oil pump. Their are two seperate chains, the engine will run just fine without the oil pump's chain, just no oil pressure. Pull the oil pan.

[350SL4spd]

happened to a client of mine. Chain broke on the oil pump. That's all she wrote. If the engine killed itself before too much damage occured (not probable, but possible) it might still turn over, just really really hard, and woul be very hard to keep running. ie: the bearings are toast, but not completely locked onto the crank and the pistons didn't seize to the cylinders. That's more or less what happened on the one that I had experience w/. That one seemed locked up solid, but only one crank bearing was seized, and it moved freely after breaking that one free. Still had to rebuild the whole motor.

First you need to determine that this is you problem. Like the others said, there are many other possible problems. But for the record, there are quite a few documented cases on the forum of that oil pump chain going and killing a motor before its time (it was a cheap single bicycle style design, not a double like the old 617s). What milage was the failure at? Seems to me most I've heard of were around 145-165k mi or that area.

Hope this isn't your cousins prob. We've all got our fingers crossed for you!

-Matt-

PS: Don't buy a used motor out of a yard unless you do compression tests first!! If one of these diesels sits for too long the rings and therefore the compression go to hell for some damned reason. That was our error. Didn't rebuild the original until after the junk yard example (65k mi) turned out to have about 50-70psi per cylinder!!!! That wasn't a cheap motor either....Live and learn!

[rdsw]

I bought the entire car from a friend, and am parting it out. The engine is a 5 cylinder turbo, with 208,000 miles on it that ran strong when I drove it the 90 miles home about four weeks ago. If you want it, I'll sell the basic block (without turbo) but with injectors for $600 plus shipping. As far as I know it has not had the timing chain replaced, so you should do that if you buy it. No warranty, but it was well cared for. The previous owner decided to buy a newer gasser wagon.

[350SL4spd]

PPS: The best way to tell if it was the chain (other than lack of OP) is to pull the oil pan and see if there is a chain in it ....Hmmm....but I think on theat model you'll have to jack up the motor to get the pan off....

PPPS: If the timing chain jumped even one cog it would put a valve through a piston and you would have heard that!!

[sixto]

Originally Posted by rdsw

I bought the entire car from a friend, and am parting it out. The engine is a 5 cylinder turbo, with 208,000 miles on it that ran strong when I drove it the 90 miles home about four weeks ago.

About the only thing the OM602 and OM617 have in common is the number of cylinders. It'll be quite a job to drop an OM617 into a W124.

Sixto
95 S420
87 300SDL

[compress ignite]

If the oil pump chain failed at any R.P.M.s you can "Pick Your Poison" as far
as expense and damage.

I am There (And while you're in there why not "Freshen Up" everything you
can lay hands or wrenches upon?)

[MS Fowler]

I finally got to visit the "dead" diesel.
It is, indeed, a 1990 300D, W124 chasis 5 cyl, turbo motor. ( Car is immaculate!)
After giving the battery a boost, we were able to get it to fire up. It ran relatively smoothly, but with a horrible screeching noise. A neighbor had removed the belts, so no accessories were turning. The screeching noise was internal. There was no oil pressure indicated on the dash oil pressure gauge. Oil level was a half quart low, but no visible debris on the dip stick.
My guess is that the noise is from dry crank, and rod bearings. Anyone been inside one of these after the oil pump chain broke? At least thats the working theory right now. I suggested he pull the engine and drop the pan and look at whats there.
What, beside the presumed broken oil pump chain, is he likely to find? If the bearings are toast, is it likely that the crankshaft needs to be turned, or are they generally not salvageable. How about pistons and cylinder walls?
Any other comments, suggestions are certainly welcome.
Thanks.

[barry123400]

Just a simple suggestion I think you know anyways. No more starting the engine so someone can hear or evaluate the squeal. Too big a chance of increasing the damage. Just my opinion.