Hello wise people of the forum,

Here's my situation. I've owned an 85 300d turbo for about a year (first Mercedes, first diesel, first auto tranny), and have gradually been learning about this great car as repairs and maintenance require.

A couple of days ago, my wife called to tell me that "dash lights are on and it's hard to steer." I told her to have AAA tow it home. I opened the hood, expecting to see a broken belt, but they were all intact. I started it, and the engine ran, but the crankshaft pulley was not moving.

When I pulled it apart, I discovered that the crankshaft pulley bolt was very loose, and the pins that key the balancing disc to the crankshaft had each sheared in half - which explained why the engine was turning and the pulley staying still. The balancing disc is now scored on the surface that mates with the crankshaft and was loose enough to pull off by hand, so I assume I need to replace it (hopefully the crankshaft surface is okay - it doesn't look bad).

So here are my questions:

1.) What could have caused this to happen? Any ideas? The alternator, AC compressor, steering pump and water pump all seem to spin freely without any noticeable play. The crank pulley bolt was loose, but it may have loosened as a result of the broken pins.

2.) My manual mentions "transferring the state of balance from the old balancing disc to the new disc," something that requires a tools and expertise that I don't have, so I called a local Mercedes mechanic to ask if he could do it after I purchased a new disc. He said that this was actually unnecessary, that the new disc will come "pre-balanced." Is he correct?

3.) I plan to replace the belts and hoses while I have it all apart. Is there anything else I should be replacing?

Thanks in advance,

Peter

Edit - Should I get a used balancing disc and matching vibration damper? Are there any problems associated with matching a new balancing disc with the existing vibration damper, which appears to have been drilled for balance already?

Double Edit - I've found posts that indicate that I'm in trouble if the shafts that the pins lie in are "wallowed out." They don't look too bad to my untrained eye on the crankshaft. Here are pics with the disc on the crankshaft. Any opinions based on the pics? My plan at this point is to replace the balancing disc, beveled washer and pins. I'm debating whether to put it all back together and hope for the best, since the holes don't seem wallowed, or have a machinist drill two holes 90 degrees from the existing holes and install two extra pins, as has been suggested in another thread. Any input would be helpful!

UPDATE I bought a new balancing disc, used the existing vibration damper, did not transfer the balance, did not drill new holes. 4,000+ miles later, so far so good... (fingers crossed)

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This is a very serious problem, potentially. If the round keyways in the crank are buggered you will not be able to keep harmonic balancers on the engine. The only sure cure is a new crank.

Folks here have tried various methods of repairing this problem but I am not convinced there is any other sure cure.

I suggest searching for threads about it as I know there are at least several.

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[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.

I've heard of this, but don't know why it occurs. Perhaps someone replaced the front crank seal and didn't get it bolted back on tight enough.
The epc shows no key, but a pin on the back.

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83 SD

84 CD

The vibration damper is balanced independently, so using the existing damper should pose no problem.

bump - parts arriving soon, still trying to decide whether to have machinist drill extra holes. Any thoughts?

I though I read a thread here somewhere where one of the Posts said you could drill out the existing holes for oversized pins (I believe for a 123).
I believe in that thread I also ask how you know that the Crankshaft Dampener is lined up on the timing marks in referance to the pointer when you are finished.
Apparently afterwards you need to pull #1 Glow Plug, Injector an Pre-chamber so you can us a Dial Indicator with an extension down to the Piston Head and get the Piston at Top Dead Center and adjust the Pointer so it lines up with Top Dead Center on the Dampner (at Zero).

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84 300D, 82 Volvo 244Gl Diesel

It's easier to pull the valve cover off and check to see that both valves are closed when #1 is at TDC. The pulley should then still match up to the proper location on the crank at that point.

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DJ


84 300D Turbodiesel 190K with 4 speed manual sold in 03/2012

That will work if you have no Timing Chain Stretch or other wear in your timing gears that would change your Camshaft Timing.
Or, I suppose if you knew how much off your Camshaft Timing was prior to the Pulley comming loose.

For example the last time I lined up my Camshaft Timing Marks on the Compression Stroke I was 2 degrees past TDC.

Also from the OPs description the holes the Pully Pins/keys went in are too big now and the Pully is now out of alinment.
Just putting a new Pulley on with Stock Pins/Keys will not aline it.

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84 300D, 82 Volvo 244Gl Diesel

The vibration damper will go on six possible ways. (The timing markings are on the vibration damper, not the balancing disc.)