What causes a stator to fail?

It looks like I've blown another stator. What could cause this? I've got a 1981 KZ1000 M1 (CSR)

good question, I wanna know too!

old age, :S
dodgy rectifier, :dry:
chain has cut through wires going to rectifier (happened to me) :blush:

Add to the list: current surges,shorted output wires by the rubber alternator grommet,less than quality workmanship in assembly,and the securing clamps holding the windings being too tight shorting out the winding.

bad grounds can also cause it

It's basically just a transformer winding. The likely killer is excess current caused by some kind of failure where the regulator is trying to supply an overload.

bountyhunter: So it is likely a short somewhere? Wouldn't a fuse blow to prevent that circuit from drawing too much current? Or are you saying it is a faulty regulator?

Maverick wrote:

bountyhunter: So it is likely a short somewhere? Wouldn't a fuse blow to prevent that circuit from drawing too much current? Or are you saying it is a faulty regulator?

It could be faulty reg/rectifier assembly. It could also be a bad battery which was telling the regulator to crank out max current to try to charge it up to 14V.

Some thoughts. Stators regardless of # of phases are simply a core of insolated wires wrapped around a heat disipating core.(eddycurrent) and are static.no motion. Primary causes for failure are 1. heat, 2.contact w. rotor,3 vibration, 4 age. Heat can be from shorted wires, high prolonged loads, high resistance anywhere between output and load. a battery w/high internal resistance, faulty reg/retifiers... contact w/rotor is obvious. vibration and age are a hard call. repeated failure points to excessive draw. insure pigtail and wiring to reg/rect are sweet, battery charge rate is within perameters. and system draw is within reason. luck G

Also there are no fuses in the circuit to the regulator/rectifier from the alternator. My understanding is the alternator runs wide open(full output) with the reg/rect.controlling battery charge and running the bikes electrical system with the excess being dumped as heat.

Another place to look is after the sprocket cover is removed, to inspect the wire bundle running above the engine sprocket in the channel. The side stand switch,the neutral switch and the oil pressure switch all runwith the three wires from the alternator.

Heat,vibration and age can cause any of these wires to get a break in the insulation possibly reducing the alternator output or causing it to short out.

10-4 MFolks... I think it's a faulty R/R. It was jumped off a car a while back which probably fried it. What's the standard bench test for a R/R? Seems like you check the ground vs. the three yellow and then the positive output vs. the three yellow both forward and back?