Larry,

If your harmonic balancer keeps throwing the bolt or other related problems, it would seem to indicate an extreme imbalance or other pulsation. Has the engine ever been apart? It sounds like it has been.

If it happens once, okay, things happen. But multiple times sounds like something that loc-tite, or maybe even welding on the front pulley can't fix.

Best of luck

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Larry Bible
'84 Euro 240D, 516K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles