N15 siezed alternator.

Gilesy

VIP MEMBER
Joined
Aug 27, 2017
Messages
192
Country flag
Glorious ride through Devon yesterday, 5 miles from home and engine locked up solid. Smoke smelling of burning guta percha coming from between engine and gearbox. Mate picked me up in van, when I drained oil from chain case it was black and smelled of burning, also lots of black debris visible through inspection hole. I took all the chaincase screws out but case with stator are firmly joined to the rotor. Any suggestions as to how to separate them without ruining case cover. I have moved it out just clear of the dowels but it is reluctant to move any more.
Thanks
Giles
 
Bummer.

Are you able to rotate the cover at all ? Maybe you could wiggle and pull it at the same time ?
 
So in the end I drilled a hole in the case and undid the rotor nut. Looking at it, there was no way it was going to come apart. Poor design from AMC, apparently the way to avoid it is turn 10thou off the rotor to guarantee air gap. I put engineers blue on the rotor when I installed it to check for clearance but there was obviously not enough air gap.
 

Attachments

  • N15 siezed alternator.
    alter1.jpg
    479.7 KB · Views: 155
  • N15 siezed alternator.
    alter3.jpg
    410 KB · Views: 160
Last edited:
So in the end I drilled a hole in the case and undid the rotor nut. Looking at it, there was no way it was going to come apart. Poor design from AMC, apparently the way to avoid it is turn 10thou off the rotor to guarantee air gap. I put engineers blue on the rotor when I installed it to check for clearance but there was obviously not enough air gap.
Hi Gilesy,
I wonder if the hole you made is small enough to thread for a Commando timing inspection cover.

Ed
 
I'll try it, although I think the metal is a bit thin. Was thinking of a rubber cap. If I mark new rotor for 30deg btdc it might prove useful for checking mag timing.
 
Glad you got it off. I agree a rubber cap will be simpler to fit and to no detriment.
 
Sorry for your catastrophe, I always thought that chaincase was suspect, even thought it was better than the press steel version.
 
Ouch!

Some of the new stators and rotors are way less than the stock 10 thou gap as supplied. Add in a little misalignment and flex and you got no chance!

These days I always measure up and then get the rotor turned down to ensure a 20 thou gap (40 thou under size). and I uses a cut down strip of milk carton to ensure a good gap as it’s being tightened.

You need at least the same gap IMHO with your cover mounted set up.
 
N15 siezed alternator.



Yes, I ended up taking 20thou off the radius which with the bit of wiggle gave about 18thou clearance. It still charges fine. Went for 120mile test drive around Devon and Somerset, it is a lovely bike to ride. Thanks for your help and sympathy.
Giles
 
Gilesy. Did you have to replace your stator or was your one serviceable?
I have just pulled my primary cover off for the second time this month to try a eliminate oil leaks. The oil was brownish both times and I could see that the rotor had been rubbing on the inside of the stator assembly. The second time the cover came off the rotor had made even more of a mess. I thought because it is not a rebuilt engine, well at least not since I've had it, that the clearance should have been correct between the rotor and the stator and since the cover has 2 dowel pins to locate it, aligning/centrering the rotor in the stator should not have changed.
I have a rotor of 74.05mm OD and a stator with an ID of 74.70mm which gives me a side clearance of 0.65/2= 0.325mm=13thou
Im thinking that getting the rotor turned down by 7thou so that I would in theory have a 20thou air gap all round unless the rotor is not perfectly centred in the stator, ( which is impossible to tell when the primary cover is bolted up).
What do you think if I was to get 10 or 15 thou machined off the rotor? Anyone else got any input?
thanks
 
My rotor and stator had welded themselves together so both scrap. Yours should be ok if you create an adequate air gap. I checked the end of the crank with a dial gauge and took a bit more off for the slight 'wiggle'. Probably worth taking a bit more than too little, Mine still charges OK.
 
Back
Top