OK, first off I am not involved, nor am I a mechanic, at least not a professional one (I could be called a shirtsleeve mechanic but I am more into electronics than working on diesels)
I have a friend that is a mechanic at least he gets paid for working in an Indy shop. He likes to look at my '87 300D and likes to visit when he sees me changing oil or something with the hood up.
He related a problem he has had with a Sprinter, an early body with the straight six engine in it, I was told it is the same as my OM603 but not sure if a turbo and not having seen it first hand I can't say that's what is really is.

But here's the problem:
The owner shuts off the engine which was running fine then the next time he cranks it it makes a noise and won't start. Towed to the shop, my friend finds the main nut at the front of the crank is dislodged, backed out. He retightens it and a few weeks later the same thing happens. He used locktite and torqued to spec but it happens a second time so he claims to have drilled and added a locking pin next to the hex and be darned if it broke that off the third time!
Now he won't work on it, or maybe the owner doesn't want to pay for all the failed effort? I don't know but I suggested maybe he has a timing problem and or a loose timing chain and when the engine is shut off it runs backward if its switched off at the right point. The way I showed him my engine stops dead in its tracks when I turn the key off, that is not what's happening on his customer's engine.
Anyone with experience have a idea what's going on?
DDH

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

I have no specific idea. When the crank damper goes bad it does not dampen vibrations correctly. So that is one possible.

This is generic, on some engines there is a cupped spring washer/s used with the crankshaft bolt that are a onetime use item.

Some crank bolts are onetime use items.

If the Sprinter engine is a mechanical fuel injection engine bad injector nozzles and uneven fuel injection can create unusual vibrations in the crank shaft as can uneven compression. What people don't realize is that when the fuel fires and the connecting rod starts down the crankshaft flexes before it moves. It needs to flex pretty much the same as each cylinder fires. That means events not happening correctly in the combustion chamber can affect crankcase vibration.

Also, once the bolt vibrates loose there is some chance the crank threads got buggered.

It is hard to give a definitive answer and paying someone that does not know how to trouble shoot the issue is going to be prohibitively expensive.

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84 300D, 82 Volvo 244Gl Diesel

thanks Diese911
I wasn't aware of one time use washers possibly bolts too.
I will pass along the info and if the engine gets fixed I will let you know, but I doubt I'll hear any more about it. Just happy I am not the vehicle owner!
my OM603 with #14 head just keeps on ticking!

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

I would imagine that the Sprinter may have an OM606 rather than the OM603.

On the OM603, the front hub has a woodruff key clocking it to the crank. The clearance is very tight, between, the hub slot, key and crank cutout. It is possible that the key may have sheared, or is missing if the hub was pulled off and then reinstalled knocking the key into the oil pan. It's very finicky due to the tight tolerances to get the three aligned perfectly when installing. For the hub to rotate off of the crank stub in either direction, the key must be sheared or missing. The bolt and washed serve only to lock the hub onto the key and should not be affected by rotational forces.

I can't confirm if the OM606 is configured the same way, but likely, it is/has been a common practice on many engines for a long time.

Best of luck

Excellent points.

I had a very frustrating woodruff key that was loos in the slot and every time I tried to put the hub on the key pushed out. I degreased the key and slot and I use JB weld Epoxy and on it and made sure it got back in the slot perfectly and trimmed off the excess and that worked. That was on a US vehicle.

After degreasing a really tight one super glue could be used.

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84 300D, 82 Volvo 244Gl Diesel

Good idea on the epoxy/crazy glue.
I ran into this problem on my OM603 when changing the main front seal at 300k mi. Luckily on that engine the key is easily retrieved with a magnet on an extension out the oil pan drain.

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Stable Mates:
1987 300TD 310K mi (Hans)
2008 Jeep Grand Cherokee OM642 165k mi (Benzrokee)