[Dunk]

1996 big block OMC's.... You want to get the serial number off the engine and take it to a Bomb dealer. Have him run the number for the work history. Certain serial number runs of the big V6's had problems with the bolts vibrating loose that hold the upper main crankshaft bearing in place. Under the flywheel on top of the block you'll see the ring of bolts in the keeper plate. Some engines didn't get the thread cutting oil complately flushed out of the bolt holes causing the locktite not to grab. Like I said it was only certain serial number runs and I think I remember some late 95's being included.

If the bolts come loose the engine will destroy the crankshaft and I've even heard of flywheels coming through the engine covers at 5000rpms.. The cure is simple. Just remove the bolts, flush the holes good with acetone and reinstall the bolts with locktite to their torque spec.

OMC had a TSB out about this, so any dealer can look up the serial number. First to see if the engine was in the serial number run, then to see if the required fix was done on that engine if it needed it..