Stator damage

plumstead0 · Post by **plumstead0** » Wed May 07, 2008 6:33 pm

I have a 500 Matchless single with Boyer ignition and 'power box'. The original 2-wire stator burnt out, presumably through lack of chaincase oil, and I replaced it with a pattern RM21. The alloy chaincase fitted flush without obstruction, but on removing the chaincase after a few miles there was bakelite swarf from the stator, which was cracked. There is a small amount of side-to-side play on the rotor when I handled it, despite the nuts being tight, and I felt by hand some knocking on the chaincase when I was riding the bike.

I was told that this could be caused by duff main bearings, a prospect which strikes me with terror. The motor sounds fine when running, with no knocking. Could anyone tell me the best way to proceed e.g. checking the main bearings? Thanks Rob

itma · Post by **itma** » Wed May 07, 2008 6:46 pm

The old age way is to take everything off the shaft and see if there is up down,sideways movement.
BUT
you stator did NOT burn out throughlack of oil, why should it? it needs none.
I would expect the cause of the stator troubleis the alternator bouncing off it.
The fact that the rotor moves is enough for me, it should be a tight push fit on the shaft with no movement when locked in place by the nut. The tighter the fit better in my view.
common problems with stator is that they become loose on the centre; the key way in the shaft is slack; there should be only 4-6 thou running clearance between the stator poles/rotor; it does not need a lot to get the parts knocking on each other, the knocking may also be compounded by a slack sprocket.
All in all I think you need to spend a wekend investigating.

plumstead0 · Post by **plumstead0** » Wed May 07, 2008 6:52 pm

itma, thanks for speedy reply! This has given me a lot of ideas for the next weekend with the bike. From previous cack-handed experience I take a minimalist approach to taking things apart, but I'll take the rotor off. Is it a big deal to get it back on and trued up? I'm using straight 50 oil. Thanks

Biscuit · Post by **Biscuit** » Wed May 07, 2008 8:05 pm

If it needs 'truing up' you are in trouble, read Itma's lips, should be a firm push fit on the shaft.

itma · Post by **itma** » Wed May 07, 2008 10:37 pm

The worst case scenario is a strip to fit a new driveside mainshaft, rotor etc.
It cannot be trued up; if its loose its stuffed.

The loose centre of the rotor used to very common on Triumphs; there are a number of mods about to get round this, none of which I have done,so cannot pontificate on the subject.
Loctite is NOT an answer.

plumstead0 · Post by **plumstead0** » Mon May 12, 2008 1:57 pm

Hi itma, I had a look at the rotor at the weekend, and I'd guess there is 5 milimetres side play on the shaft (i.e. I grab it from front on, and can rotate it 5mm).It also rocks for-and aft (towards and away from me) slightly - about 1 mm I'd guess. There are two large nuts on the end of the rotor which are tight. It seems to be slackness of the rotor on the shaft rather than shaft movement, but I I'll have to get the rotor off to inspect further. From my description, does this help with diagnosis? (i.e. would a new woodruff key be useful to have when I next get to the bike?). I have a spanner to fit the nuts, but was wondering how I could get away without the special tool? Thanks Rob

itma · Post by **itma** » Mon May 12, 2008 2:36 pm

What special tool?
you should only have trouble if a previous owner has loctited it on;
Yes you will need a woodruff key, lets hope you dont need a shaft, you might need a rotor tho.
As for the end play, that might need some further investigation.
Hopefully its just the rotor thats stuffed, the body comes loose onthe central core.

plumstead0 · Post by **plumstead0** » Mon May 19, 2008 7:43 pm

Re. wobbly rotor causing stator failure on my G80, the rotor was removed to reveal a worn slot where it fits over the woodruff key and onto the shaft. Here's hoping that rotor and stator (£90 inc postage) will be the end of problems. Any advice on ensuring this will be gratefully received e.g. fitting/checking before I fire up the bike

itma · Post by **itma** » Mon May 19, 2008 10:49 pm

If the slot in the mainshaft is at all worn, it will only be an interim solution.
The key needs to be a tight fit in its slot.
If there is any slack it is possible there may be some kind of trick Loctite about to help out, but I am not au fait with what is about these days.

plumstead0 · Post by **plumstead0** » Tue May 20, 2008 3:03 pm

ITMA, the slot in the shaft is OK as far as I can tell, it's the slot in the rotor (keyway?) that is worn. I'll find out on Friday night if it's OK, when the new rotor and stator will have arrived. I've just use JB Weld (glue) to successfully repair a range of rust holes in a Yamaha tank, so that would be my choice to reduce the play in the mainshaft slot