No sniggering please, this is the motor on my "Dakota" wet grinder (AKA the "Tormekkalike").
It's been neglected for a while - just used/abused - so I've taken time to do some maintenance. Mostly concentrated on the main shaft - de-rusting, greasing the bearings, etc. but...
The motor isn't happy. On startup it stutters and causes the machine to vibrate (does this even under no load whatsoever). Left to its own devices, it does settle into smooth running usually, but sometimes not.
Its bearings are in ridiculously good nick - if off-load it runs on for ages after you cut power to it, but not always.
So might a faulty capacitor cause these symptoms? It's a very small induction motor, rated at 110W @ 240V. The capacitor is 4uf @400V (rectangular potted block), which I have no way of testing*.
The only other thing I can think of is a dodgy connection to the motor: it's on a "pendulum" mount - the shaft is horizontal and the motor hangs down from a parallel shaft so it can swing towards or away from the rubber tyred wheel that's on the main grinding wheel shaft (it's a friction drive). Imagine the idler drive of a record turntable, turned on its side. Because of this arrangement it's easy to run the motor under no load at all, and the vibration/stuttering is independent of the load the motor is under.
I'm just about to put an AVO on it to see if I can prompt a poor connection by wiggling leads - nothing visibly wrong from inspection. I'll post some pics later if that helps (or if I find the cause isn't the motor wiring!).
Ideas welcome.
E.
PS: If anybody can recommend good brands of motor cap. or ones to avoid please say. The current one has a date code of 2011, so probably doesn't owe me anything...
(*well I don't have a capacitance meter to do it)