This has me stumped. I was cutting a piece of half-inch plywood on a
contractors' table saw. The piece as about 15" wide. I was most of
the way through when I started to hear a sound that was a little
louder than usual. I completed the cut, and as soon as I did, the saw
began to squeal very loudly.

I turned it off and checked. Nothing wrong on top, but when I looked
at the back, I saw that the motor had fallen all the way down. The
motor pivots, and a screw in a slot usually keeps it from dropping too
far. The screw had broken off. But of course, gravity usually keeps
tension on the belt, and the belt holds the motor up.

I checked everything I could. All screws were tight. The motor
mounting plate appeared to be in the same position as usual. But the
belt was suddenly way too long to hold the motor up. (The squealing
sound was the belt rubbing against the saw housing.) I use a link
belt on the saw, so I tried removing six links. When I put the belt
back on, the motor was back into its usual position. (I replaced the
broken screw too, even though it doesn't actually hold anything). I
tried making a couple little test cuts, and it seems to be fine.

Can anyone explain what happened? I had been using the saw all
afternoon, and everything had seemed fine. I can't imagine that a
link belt could suddenly become a lot longer, so something else must
have happened. Can anyone think of an explanation? Is there anything
I should check before using the saw again?