Hard to say what is going on without seeing it, but all of the pulleys
are mounted to the engine, not the frame.  It is hard to see how a
frame problem would cause the belt to jump or shred unless it was
making contact with the vehicle.

Taking a wild stab, I would guess that the new engine was in an
accident in the original vehicle.  (Pretty good bet because otherwise
it would still be in the original vehicle.)  In that crash, the engine
was impacted and something on that engine was bent or broken.  The
shop is missing it because they are looking for damage from your
accident.  I would also guess that they are dishonest, incompetent or
both.  If you can see that the pulleys are out of alignment, it should
be easy to figure out why.  Take it to a honda dealer and ask them to
look at it.

I rear-ended a very nice lady in an old Ford Bronco and about 25 MPH.
The front end of the minivan looked totalled, but my insurance
appraiser said that it was a very straight-forward procedure to replace
the existing enine with another from a different Odyssey. He told my
wife that we would "never know we were in an accident". Since then (9
months) we have had to have the van back into the shop 3 times because
the serpentine belt keeps coming off. There is a bolt near the
alternator that mounts to the engine block and the bolt has broken
twice now. And, the last time, our trans fluid was completely gone and
we had a leaky shift shaft seal. I can clearly see that the belt
*wheels* are not aligned and that this is why the serpentine belt keeps
shredding.

Anyway, I think the insurance appraiser messed up and missed that the
frame was bent in the original accident. But, I am not sure that I can
prove this. I am wondering if anyone has had thier engine completely
replaced and whether or not they are having similar problems. Also, any
general advice would be much appreciated. Thanks!!!!