Join Date: Jan 2019
Location: Central North Carolina
You should check the wiring connections inside the motor box to be certain that It's wired for the correct voltage. In many cases, the wiring diagram is on the inside of the motor electrical box cover. Don't try to run it unless you are certain that it's wired for the voltage that you intend to operate it at.
I would be willing to bet that your problem is either the capacitor or the centrifugal start switch. These are usually inside the non shaft end of the motor or the end where the power wires enter the motor. Inside, on the motor shaft are two spring loaded weights that swing out as the motor rotates. When they move, they press on the switch, opening the circuit to the capacitor and the start winding in the motor as the motor accelerates up to speed. If the capacitor is bad or the switch contacts never closed as the motor slowed down the last time it was run, the motor will only have power on the run winding when you try to start it and it will only hum. It needs both the start and run windings to be energized when power is applied and this switch disconnects the start winding as the motor comes up to speed, because the starting winding will over heat if not turned off. Cleaning the flyweights and the collar that slides on the shaft so they move correctly, or cleaning the contacts of the starting switch is an almost certain fix, but capacitors are cheap, so I would change it too. Buy one with the same ratings that the label on it says. There will be a number followed by MFD and a working voltage (must be AC, like 370 volts AC) and the physical size of the capacitor must be the same or it likely won't fit inside the motor electrical box.
To remove the end cover of the motor there are 4 long bolts with nuts holding both ends of the motor together and against the center winding part of the motor. Remove these 4 bolts. Then tap the edge of the motor end cover with a large screwdriver and small hammer around the edge where it joins the center section of the motor. It would be good to scratch a line across the joint, so you can remember the orientation of the motor end cover when you are re-assembling the motor. The switch will most likely be mounted to the inside of the motor end cover, so be careful with the wires as you remove it. Clean the switch contacts. A small piece of emery cloth or a small file between the contacts and slid back and forth will work. You want them to be shiny and not heavily pitted, but they must spring tightly together when you finish. Then clean and lightly lubricate the fly weight pivots and the sleeve area on the motor shaft. A tiny bit of lubricant here helps too. The sleeve needs to slide freely on the motor shaft, but go easy on the lubrication. You don't want it flying off as the motor spins.
When satisfied that the switch and fly weights are OK, replace the capacitor and finish re-assembling the motor, making certain that no wires interfere with the motor rotation. Spin the motor by hand after assembly to be certain that it spins free. Then try it out with power. I think you will be very pleased with the result. If you fail, let the motor rewinding shop look at it. They might just see an easy fix for it.
Local motor rewinding services will have the capacitor and even switch parts. Capacitors can also be had from Grainger and other Industrial Supply companies.
I worked 7 years as the only US based (EE) factory electrical rep for a European Printing Press Manufacturer. My territory was all 50 States and the Caribbean. I worked on a lot of motors during that time.
Last edited by CharleyL; 08-14-2019 at 07:27 PM.