Here's a picture of the compressor in question: Don't believe the 7 HP marketing bullshit; it's a 4 HP motor. The pump itself is an oiled iron-body USA-made model that's supposed to last a good long while. Nothing else in the pump has any axial play. The reason it was so cheap is it was sold to me in almost-running condition; the guy had robbed the pressure switch and some plumbing to fix up a beast of an old Qunicy 2-stage compressor. (I in turn robbed a pressure switch and some plumbing off another air compressor that well and truly shit the bed.) I've been trying to figure out how the conrod failed; there's a burr on the crank journal, but I'm not sure if that's what caused the failure or if it's a side effect. The rod looks like it got twisted and then it grabbed the crank and shattered. (Behind the compressor in the picture are two 25 gallon tanks that put me at 110 gallons of air storage, which is quite nice when running a die grinder or the like.)
Die grinder is about throughput. I guess you can make that up by storing a hundred gallons of air. Certainly cheaper. It probably failed because the guy raiding it for parts let the oil out. At least, I would consider that a keen possibility and recognize that the rod isn't the only part to fail as a result, just likely the first. A 7hp replacement pump looks to be about $750. That kind of money gets you big boy toys. I would save the motor, take a zipsaw to it and put it in the recycle bin.
There are only about 4 other moving parts in the whole compressor, and they're all in good shape--no axial play at all. A new con rod and one crank bearing (that I need to remove to install the conrod, plus it has a wee bit of wobble to it) is under $50. I think I can deal with that. I can replace this pump new for about $300...$750 would get me into a very nice 2 stage pump. I'd love to do that but I have other things to spend that money on...