ATLAS Alternator rotor/stator/charging problem

I bought a new rotor from Rex's Speedshop (which luckily is only 30 mins drive away from me) Really nice helpful guys they are too. It slid on the crank shaft nice and tight.

A friend gave me a used stator that appears to be in good condition and he said was a good 'un. For my own peace of mind I got Luke at Rex's Speedshop to test it and it passed no probs. Trouble is, when its bolted on I just can't get a minimum air gap of 0.008" all the way round. There's always ONE segment that the feeler gauge wont slide into and it's always in the same spot even when I turn the crank. 

I noticed there's a very tiny amount of play between the studs and the stator holes once it's been slid onto them, so I inserted THREE feeler gauges and slid the stator on over the rotor, tightened up the three bolts then removed the feeler gauges, but the problem persists. One segment is always less than 0.008".

I've checked the crankshaft runout. It's true as a die, as is the rotor when it's bolted on, so I can rule out crank bend.

No matter how many times I try I just can't seem to get a clean gap air all the way round. I can only summize that the internal diameter of the used stator must be slightly warped, though I can't see any fluctuations when using a Vernier gauge.

Tomorrow I'll go get a new stator from Rex's Speedshop and see if that solves the problem. If I can't get a decent airgap after doing that I guess I'll have to investigate if the stator studs are bent.

Also, the three stator nuts are supposed to be tightened up to 15lb ft (20.3 NM) per the Haynes manual, but it feels like they're going to shear off if I go that much, so I backed off on waiting for the torque wrench to click fearing I'll damage the studs.

Hopefully, a new stator will do the trick. (Famous last words!)

Interesting idea. I'm not a metallurgist but wouldn't machining down the thickness of the stator bolts weaken thier tensile strength and require that the lb/ft torque needed to tighten them be reduced? (i.e. less metal, thinner stud, more stretch) I might be talking b******s but that kind of makes sense doesn't it?

These studs do look a bit fatigued to be honest. I can almost 'hear' them stretching as I tighten the nuts up, and the bottom one is a bolt/stud as it's been wound out of the base, not that that should really matter. 

I'll try the new stator tomorrow and if that doesn't sort the air gap out I'll concentrate on the studs

I suppose it's always going to be a bit touch and go fitting a used stator. Who really knows what punishment it's endured even if it does test well and look relatively ok. If a brand new one doesn't fix the air gap problem it can only be the studs or summat up with the base plate that the stator bolts to. It may be slight skew-wiff by just a touch. I really hope not. 

I think I've done it.

Before I went ahead and bought a brand new stator I gave it one last try with the used stator that a friend gave me using Alan's method. I found an old aluminium head gasket in the scrap metal bin that came off a 250 GT Suzuki I was restoring, cut three strips from it, loosened the stator and slid the strips in then pushed the stator fully home, tightened up the three bolts then pulled the aluminium strips out. I then turned the crank through 360 degrees checking all the segments as I went. The 0.008" feeler gauge slid in on every one. It slid in a bit tighter in a couple of places but still, it slid in, so none of the segments are less than the minimum air gap tolerance allowed. Phew! 

Grant, I too would like to see a slightly bigger air gap but I haven't got a lathe and I've now got the air gap to it's minimum tolerance so I'm going to go with that, though I'm definitely going to re-check it after running the engine!

Started the engine. The bike is charging and the low voltage warning light is working properly again, i.e. it comes on when the ignition switch is turned on and goes off after 1500rpm

Result!