Automobile;
My mechanic just told me that as he was trying to take out the engine from my truck so that he could work on the truck, the engine wouldn't turn. What are the likely causes? The truck was in a collision.

Your mechanic should be able to inspect that for you. We can't see the engine to assess the damages, if any.

Jammed flywheel or pulleys. Did you hit someone? that would be a logical reason.

Why doesn't your mechanic know WHY?