Problems after 603.971 engine rebuild.
 

I took my 1994 S350D to a mechanic who specializes in German car repairs. The engine had a cracked head. I'll skip the details of the horror story but the mechanic blew the engine up twice (valve/piston interference) trying to get it right. Three was almost the charm. I've had the car back for about 6,000 miles and the engine seems fine in all respects except one. When idling, the engine shakes the whole car. I guess the best way to describe it is, "zug zug zug zug". You actually bounce up and down slightly in the seat while its doing this. The problem is minimal when the engine is cold and more pronounced when the engine is up to temp. Higher ambient air temperatures also seem to aggravate the condition.

I've noted two things about the car since the "repair".

When I first received the car back, the vacuum line were all screwed up (hard gear shifts, turbo not boosting correctly). I fortunately had photos of the engine taken prior to this misadventure. Using the photos
I was able to correct the vacuum line problems (I think).

The other thing I noted was, when replacing the valve cover gasket, I found the timing chain was very loose (sagging on the driver side) and the tensioner appeared to be near or at full extension. The mechanic had replaced the timing chain.

I'm probably going to take the car to the local Mercedes Dealer, but I'd like to have an idea as to what the problem could be. My local dealer is not exactly a whiz with diesels. Once after having the dealer replace some glow plugs, I noted the car had a very rough idle. I marched right back in and pointed out the problem. The service manager discussed the problem with the "technician" and told me I was probably looking at a new injection pump. Fortunately I have a father-in-law that's worked on everything from lawn mowers to locomotives. He said "they got air in the fuel lines, run it for a few days, it'll be fine". He was correct.

Any ideas out there as to what could be causing the rough idle? Is there something specific I should have the dealer check?

Thanks

Location, location, location
 

I feel for you... although I can't offer good diagnostic advice on your problem :( (the universe of possible problems is large when someone as incompetent as your prior mechanic has had free rein), I would suggest that you post your location so that someone from the forum can suggest a competent mechanic in your area.

If you are up for doing some diagnostic work yourself, one place to start is to see if there is one particular cylinder that is somehow not contributing, either because of air in the line or low compression, or valve clearance messed up. One way to do this is to crack (loosen) each hard injector line one at a time with the engine idling, and see if the engine problem DOESN'T change. Cracking a line should deprive that cylinder of fuel, and should make the problem worse, or at least different. If you crack one and nothing happens, then you have narrowed the problem down to something involving that cylinder.

Kurt

Timing chain should not be loose at all, I would not drive the car.

Are you positive this 'mechanic' was a specialist? I am sorry, but if the person cannot time the camshaft to the crankshaft and ROTATE THE MOTOR BY HAND to feel for interference, this person should not be calling them self a specialist in anything.

The .971 is well known for bending rods and making cylinders ovate. This should have been inspected closely when the head was removed before moving forward with the repair job.

Seems to me you have a multitude of issues going on... perhaps camshaft out of time, low compression on a cylinder, improper head installation, etc. Why on earth the timing chain was allowed to be slack with the motor running is beyond me.

I would not drive the car (AT ALL) until it is gone over closely by hand via knowledgeable person to prevent further damage.

From your description, you took your car to someone who specialises in CLAIMING to know about German cars (cos, you know, german cars are different to american cars or french cars, entirely different laws of physics apply, things are made out of anti-matter so you can't even use an american made 13mm combo spanner on a german made 13mm fastener) but who in actual fact probably isn't even competent to pump gas.

You are now in the joyous situation of not knowing what the problems are, and not knowing which new problems your "mechanic" has created.

All the "work" done so far needs to be done again, properly, and any additional damage (guaranteed to be some, if not more) done by your ****ing idiot "mechanic" also needs to be repaired.

Hopefully you will take the bill, and engineer's report from this repair, and sue the "garage" your "mechanic" works at for every penny, hopefully driving them out of business.

Thanks for the replies. I'm located in Rockford, Illinois. If anyone knows of a decent diesel mechanic in my general area please advise.

I'll try cracking the fuel lines as suggested. As far as legal remedies go, I'm in Illinois, the most I can sue for is the market value of the car (on a good day that would be $6,000+/-).

The engine was checked for bent rods and elliptical cylinders when the original head was removed. All was good. Of course after two catastrophic failures...who knows without tearing it down again.

My goal is to drive the car for one more year without dumping a ton of money into it.

Not to be the barer of bad news, but I do not see this happening. At all.

Send Guido to talk to him. Perhaps he will refund your cash.

I'm sorry to hear of your troubles.

Many things could be wrong, and are covered above. I am curious what "blew up the engine" means, as far as what happened, what was damaged, what was repaired, and what was checked after these failures.

Also, if you find it not worth repairing, someone here will want to buy it.

Before you start your engine again you REALLY NEED to make certain that the timing chain is how it should be. If it is as slack as you say you are in danger of repeating your previous problem of pistons hitting pre-chambers(?) and valves...

If you don't fancy letting the dealer see the car and nobody on the forum can help I'd talk to some other diesel mechanic - think trucks / buses / tractors. Not ideal but seriously has to be better than the guy who built it (if he is as bad as you say).