If it's a mechanical seizure then there are at least 4 possibilities a) Armature has expanded (unlikely if it frees off) b) Bearings are seized (possible but unlikely c) Swarf has entered the motor (they are not sealed motors) and is jamming the armature against the stator d) The centrifugal switch has disintegrated and is jamming the armature A capacitor failure will not cause motor seizure
Do you hear any rubbing or grinding noises when you turn it by hand and once if frees off does it turn freely. Once free does it run
The test Kieth suggests is an excellent one, because it eliminates anything to do with starting windings, capacitors and the centrifugal switch. If it still locks up, then it's almost certain that the armature is being pulled out of its central position and there's metal to metal contact with the stator. I've seen this many times on high speed spindles which spin freely until the power is applied. The problem exists in all types of motors because the clearances have to be very small to get the best efficiency.
Most motors have one fixed bearing and another in which the outer cage slides in a pocket with a wavy washer behind to create the necessary preload. It's possible that the bearing outer is stuck in the housing and there's no preload, although I'd be surprised if that was enough to allow sufficient movement for this problem to happen. Sliding the motor shaft axially while moving the lathe could cause this to happen. Anyway, it looks like the motor needs to come off to inspect and grease the bearing housing and check it's all moving as it should.
I'm voting for the swarf hypothesis. There's no guard in your picture, and the lathe/motor has been moved, possibly dislodging a hidden strand. As noted, the internal clearances are tight. If you're lucky a blast with an airline might clear it, otherwise it's covers off.
Are the shaft bearings oilite type sleeves or ball races. If sleeve bearings and seriously worn, they may permit the rotor to touch the stator. Can I suggest you check each for wear and if badly worn, replace them. Also check the lubrication channels to ensure oil can reach the bearings. On one of your photos the drive-end lubrication port appears to have a slotted plug fitted
Ahh! sweet Success, Rob! now, off to the workshop with you, Lad! and make up a nice pile of scarf to have scones and Tea by! do You do have a pot handy for those wintry nights? I wish myfords were not so hard to find here in the “Colonies”. Post a picture or two of your “precious”! congratulations!
You don't show the rotor but it looks more like a slip ring motor where the mains is connected to the rotor and the stator. The usual alternative is a squirrel cage motor where the mains is connected to the stator only, inducing a current in the rotor. High starting torque withthe slip ring but low efficiency.
That's the centrifugal switch you see in the background. The two bright faces are the 'rubbing' face that contacts the rotating mass part during start-up only. The actual switch is at the bottom of the yolk and will be open with the rotor removed. Extremely unlikely the motor would have a slip-ring rotor. The stator laminations show show signs of contact by either the rotor or debris within the air-gap.