I was vacuuming leaves the other day when the "6.5 hp" Harbor
Freight-powered vac let out a terrible bam-bam-bam... and started
slowing quickly. Quickly shut off and locked tight. Oh, crap! Up to
my ass in leaves and a broken vac!

It had to be the engine, of course, but when I got it in the shop, I
found this:
http://home.comcast.net/~bobengelhardt/DSCF1165.JPG

When the blade failed, its backing plate bent and the blade tip started
hitting bolt heads in the case. All the blades had real cracks - one is
circled - and were not far from failure. I can think of no other reason
than centrifugal force. The blades are about 3/16" thick - pretty
surprising that they would crack like that.

Now, here's the best part: I had a spare impeller in the shed! Who
keeps spare impellers? Impellers don't fail, why would anyone have a
spare? You're looking at him, as they say.

Fixed in a flash and back to the leaves. Very satisfying.

Bob