The first order of business is to uninstall the old motor. That’s pretty simple: unscrew the wires in the junction box, pull the four bolts that hold it to the head, and lift it off. At 50 pounds, it’s heavy but not too difficult (note I’m 6’2″ and 230# — possible bias).
While I’ve got the chance, I’m going to pull the gears from the stock drivetrain out of the head. This will remove a little weight (any more weight I can remove is a good thing — the new motor is 100 pounds), but most importantly it will prevent the gears from engaging by accident. It’s also a good opportunity to drain the oil from the head.
Gears and gearbox cover pulled off the mill. The shaft closest to the top is the motor driveshaft, the second on is an intermediary that transfers power to the high/low gear shaft, which is the one laying down. The final shaft is more of a collar that fits onto the spindle.
Here’s the inside of that shaft. It looks like this part was made by pressing a few separately made parts together, although I’m not 100% sure on that. It’s certainly a complex part, with the internally broached keyways for the spindle spline and two sets of gear teeth.
This could probably be removed at this point, but I left it in since it liked helps to stabilize the spindle. This will be particularly important once the belt drive setup is applying force all the way at the top end of the spindle.
Here’s the top of the spindle. That cover (covered in oil, with the three screws, around the spindle) is the oil seal, which I’ve left in for now.. I’ve drained most of the oil out at this point (into the pan below the head, somewhat visible).