Stator clearance and adjustment

Ok I know its been covered a few times but I was wondering what is the most practical way of achieving reliable clearance.
I run a belt drive so no oil. A Wassell stator lasted 4-5k miles. The replacement Sparx 21k and the most recent (July 2015) 'Lucas/Wassell' 2k. All inevitably (it seems) crack around the poles, the encapsulation swells and the rotor contacts the stator in the swollen areas. My feeling is that that increased friction causes the stator to overheat further. The first Wassell ran in oil but with an overvoltage zener, and later the belt. The Sparx ran with an electronic reg and needed a bit of extra clearancing to stop the encapsulation picking up on the rotor. Stupidly I didn't do this with the 'Lucas' as it had lots of clearance all round, not the same round 360 degrees but plenty. Its not total toast but cant handle more than ignition load. Its well on its way. It has picked up slightly on two poles, only a bit but enough. I measured the stator, bore, rotor od and checked clearance side to side. Its only 018" total on the inside but 033" on the inner edge (feeler guage). Thats with the rotor sitting in the stator and pulled to one side.
So back to the question.....to do the job properly should I try bending the studs? or ease out the mounting holes in one plane. Basically it needs to move forwards at 09.00. Whats the consensus gents? BTW the mains haven't gone and the rotor is a good fit on the crank. Its also round and concentric with no magnets lifting (11/96 date code). Alternatively use a flap wheel to achieve same at 8 to 10 o'clock?
Would like to fix this one for good, always been an issue but seems to have been managed ok till the recent replacement (although obviously the Sparx was not happy). It sort of makes me wonder if the Sparx had better class wire insulation than the Lucas allowing it to survive under less than ideal conditions.
I worked for Lucas and a US DC motor manufacturer for 35 years and to save a few pennies we always used Class A 105C wire on the windings when possible. 155C Class F was for special cases but those motors rarely burnt out if applied correctly. Thanks as always in anticipation of helpful responses .

Hi Keith, it happens to me several times....and as you fed up with clearances "huge" diferences (due to different reasons), at the end "my own wild solution" was to turn down the rotor , till the tolerance was ok , of course it ends up to some BIG clearance in some way, but GOOd one where needed, sure I will loose some charging amps , but no burnt stator , and even better no crankshaft end bent due to seizure of rotor versus stator, sometimes I succeeded to enlarge the holes of the stator, so it could move , fit some spacers (beer can , X ray radio or whatever ........), and it works .............!

Get yourself a small round file and file the mounting holes in the stator to suit the direction you want it to move.
I wouldn't go bending the studs or reducing the size of the rotor.

I would only turn down the rotor as a last resort. Slightly enlarging the mounting holes makes more sense. I use a liter size soda bottle as a shim to set an even clearance. Chop off the top section leaving yourself about 2-3 inches of sidewall and bottom. Slide this over the rotor and install as usual. You'll then have even spacing around the entire rotor. A lot cheaper and more readily available then running down to the bearing supply house and buying a sheet of shim stock especially if you live on an island as I do.

Good idea that - to be filed away in my List of Things to Remember...

Cheers,
Steve.

Thanks for that guys. I've cleaned up the encapsulation and lost the taper side to side. Like eskasteve suggests I used a plastic milk container which is 0.014". That just fits and will come out. I know I had good clearance when the stator was fitted so hopefully I've gained a bit. It's almost like it has to cure and do its thing, then has to come off to clean up! It is charging but will only deteriorate so I guess I have to get another, clean up for max clearance, run for a while and remove and 'fettle'. I may do the hole enlargement. The stud bending is a non starter for me now I looked at it closer. I notice on the Old Brits site that the 3 phase needs 0.018" clearance. Does that indicate something with the higher output units?

Well I bit the bullet and bought the original stator brand that had lasted OK. Good clearance all round at 15 thou (much more than before with this brand) but a bit chunkier in the encapsulation! Result = no clearance between back of stator and belt pulley side shield. I was so busy getting the radial clearance checked I'd failed to notice the new stator was 100 thou deeper from mounting face to the back. Just be warned in case any belt drive users out there fit one of these. I've told the supplier and it was my fault I didn't check but I'd had no issue there before. The sanding marks are after it overheated and left a ridge at that end. I think I caught it in time but here's the damage.... smelt nice :roll: At least it charged OK even with 15 thou + clearance.

I know I will get plenty of flack for this ...I have run into this problem a million times....a lot of clearance on one side and almost nil on the other. I use a dremel to shave the stator to achieve the proper clearance. All its removing is some plastic and possibly .006 off of the laminations in that spot. It's better than having it rub. I have found no better way to do this.

No flak from here. But this time I had loads of radial clearance just nada side to side. The stator was pressed hard against the toothed pulley side plate....2nd picture which I've linked properly this time. Three 60 thou flat spring washers moved it enough but now the rotor is too deep. Still, it charges well enough at 3000 + with all lights and ignition.

eskasteve said:

I would only turn down the rotor as a last resort. Slightly enlarging the mounting holes makes more sense. I use a liter size soda bottle as a shim to set an even clearance. Chop off the top section leaving yourself about 2-3 inches of sidewall and bottom. Slide this over the rotor and install as usual. You'll then have even spacing around the entire rotor. A lot cheaper and more readily available then running down to the bearing supply house and buying a sheet of shim stock especially if you live on an island as I do.

Click to expand...

Cut up beer cans work well as shims also

The problem with drilling out the stator holes is that if the stator decides to shift there is nothing preventing it from hitting the rotor. That would be disastrous.

I tweak the studs to get clearance using a small piece of pipe, probably 6" long maybe 1/2" ID. I've done this probably 50 or more times in the time I've had my bike.

Bending the studs is likely to end up with a broken casting post. I drilled the holes out larger but be careful doing this as the drill will grab and screw it's way through the stator. set it with the soda bottle spacer and once tight, why will it move?

It has been running well for a couple of months months now. The radial clearance was huge in the new Sparx stator (0015" +) that wasn't the issue with this one. It was the wider encapsulation that clashed with the drive pulley sideplate as per pics. Not a problem with the std chain sprocket. However an earlier Sparx was no wider than the current Lucas/Wassell items. Only a point to consider for us belt users!