At the quarry I worked at in MD, our drilling rigs ran 12v71 detroits for the powerheads. I hated listening to them scream all day. They would turn a constant 3 grand for 10 hour shifts.
Sorry... I don't think of servicing one in terms of "tune up", but that's just me.
You want to really cuss at one? run it out of fuel and try to get it going again with no air.
I watched him move a truck from one side of the shop to the other on it. (the truck had something wrong with the fuel system I don't remember what though it's been about 4 years a go)
Nope never saw a bent rod, but I did get to see a 60 block with a hole you could put your fist through though. (driver never heard a thing till it blew)
This sucker got hot (lost coolant thru a pinhole in the coolant filter) sucked a sleeve, and when it FINALLY died, richard cranium tries to start it with ether!