Picked up my new Baldor Buffer today and Dayton 3/4 hp Bench Grinder

WOW is that Baldor Buffer AWESOME! The most phenomenal thing I've ever used it makes cleaning up my vises EFFORTLESS.
The big Dayton (8") grinder scared me

though. One of the wheels had a chip out of it so I stopped at Home Depot and got a new 8" wheel. Mounted it with the shims, tightened it, but not too much, and started the grinder to seat it in...BANG...the damned wheel exploded in half. What could I have done wrong, could it have been a bad wheel???
Last thing, and a little off topic, on my way out the guy sells me a Kalamazoo 2" Baldor powered Belt Sander for $50.00. Motor didn't start well, had to be coaxed. Got it home, cleaned the capacitor connections, runs great. I'm ordering a new OSHA guard from Kalamazoo, other than that it's great.