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)

Attached Thumbnails