Rotor question

[mikeydpippin]

Dave. Have just written a detailed note but lost the lot as the site 'timed out'.
In short, one pal recently had his engine lock up as the rotor overheated and 'welded' itself to the stator.
Another pal recently struggled to fit a Wassell stator and rotor.
After a lot of trial and error, head scratching, and relieving of the high spots of the rotor he put the rotor on a dummy axle in his lathe and found that he had to turn down the rotor by 25thou to make the circumference of the rotor concentric with the axis of the shaft.
He reckons he now has about 25 to 30thou clearance and gets near as dammit full output from the alternator.
(As a side point when you wrap tape on the rotor the ends must be butted, not overlapped).

The root of these problems seems to be poor quality control by the rotor manufacturer, making the 7 (?) thou recommended clearance within the whole assembly virtually impossible to achieve accurately or with any confidence.

No obvious movement from crank with engine running bodged a marker with a plastic zip tie, touching the crank the zip tie didn't move.
I have asked an engineering company to take off 5 thou ( 2.5 each side) but looking at Neville's post maybe I should be asking for more to be skimmed?. Really don't want to overheat the stator.😩😩

[Mick D]

Hi

I would have expected the clearance between the rotor and stator to increase as they warm up - if the rotor periphery is concentric with it's bore then I'd aim for around 0.010" clearance when cold.

Regards Mick

[Rangy65]

Unfortunately i found out that the clearances do close up when the unit warms up. (See picture). I originally purchased the stator as a direct replacement for my 1961 G3.

I didn't know that there had been an increase in diameter so with the original rotor the gap was far too big and so very poor output. I called the firm that supplied the stator who cheerfully informed me that i needed a new rotor. Step forward a week and i had fitted the new parts.

On the bench the G3 worked well great charging no tell tail noises or smells excellent! Out for a test ride and 20 miles later the engine seizes. Well it wasn't it was the alternator as a unit.

Back on the phone i complained to the dealer - sorry pal its your fault for not checking the air gap between rotor and stator.

On club night i mentioned this and was informed that this has happened before and to skim 2-4 tho off the rotor.

I put the old stator and rotor back and its worked since - although i do use LED bulbs.

rotor2 (1).JPG

well lesson learnt.



Cheers

Steve

[SPRIDDLER]

I would have expected the clearance between the rotor and stator to increase as they warm up -

From memory the problem was that the heat generated by the intermittent contact between the rotor/stator softened the insulation or the potting medium in the stator which oozed out like toffee and after the bike had stood for an hour or two it cooled and locked the two together. It wouldn't turn over at all on the kick starter. Not sure how he got the outer chaincase off to sort it though. I'll ask when we meet up later this week.

[Mick D]

Hi Nev

That is a more plausible cause

Thanks and Regards Mick

[GrimJim]

This is one solution.

Regards
Jim

[mikeydpippin]

Just to update this thread.
I had 16 thou (total) removed from rotor, fitted to bike 59 G3 and no charge connected both wires one at a time leaving stator in turn to multimeter and earth on bike (disconnected from loom) and had 0.9 showing as continuity when I connected both wires together,( I believe this should be O/L)
With engine running checked voltage across battery + and - and showing 2.50v ( even though battery has 5.80v ) so a discharge. I then disconnected stator and did check again and I had 5.80v so the stator is pulling from the battery.
Not sure if damage was done at the first attemp before the rotor was skimmed, but the casing outside the stator is getting fairly hot.
Any further checks appreciated before I give up.

[clanger9]

The stator coils must be open circuit to earth. If there is continuity to earth, the stator insulation has failed.

[mikeydpippin]

Thanks Paul,
I have two options.
1,give up
2, have another 10 thou (total) removed from rotor, and buy another stator ( not cheap)
But not confident all will be okay as even after skimming the primary cover is fairly hot outside stat9r.

[clanger9]

Once the coils short to earth, it causes maximum current to flow in the stator, resulting in it overheating (and of course further damage...)
It is possible to repair a damaged stator (so long as it's not too “cooked”), but it's tricky. The first thing is to find where it's shorted to earth. If you're very lucky, it might be a simple matter of bending the copper wire away from the stator frame, or cleaning away any metal swarf that's got lodged across an insulating gap...