617 balancer plate shear pin failure

[Telecommbrkr]

Hello All,

I am new to this forum, and am glad I found it. I have been a member of the Benzworld forum for awhile but the tech expertise of the users on that one does not compare with the members posts that I have been reading here.

Anyways, on to my challenge...

...I have an '82 300SD bought it with 270K US miles. Drove it like I stole it for over thirty-thousand miles. One day I lost all accessory drive ( as in all the belts on the engine stopped turning, but engine is still running), turns out that the two dowell pins that locate the harmonic balancer onto the end of the crank-shaft cut in half. Replaced them and drove again for a few thousand miles. It happened again, I repaired again. It happened about five times and then I determined that the 'keyways' that the pins sit in were wore from cutting all those pins and that I was going to need to get my crank-shaft replaced or machined. Figuring that was going to be the same or more expensive than finding and replacing the engine with a used one, I did.

When I installed the engine I put brand new shear pins ( as I have learned what the official name for them is here in this forum) in when re-installing the engine.

I thought all my problems were solved, enjoyed the newer less miled engine for about five thousand miles and it just happened again!!!!!!

I have found topics that dealt with this happening to one of the members cars, and read all the detail in the repair. Nothing too much new in these as I have done this repair so many times I could do it blind-folded!

Does anyone know what causes this to occur?

What can I do when repairing this (yet again!!! ) to avoid it re-ocurring?