C15 alternator rotor

[Barnsey]

I bought a new tab washer to go between the nut and the alternaor rotor on the end of the crank shaft.
However, Having done up the nut the rotor is still rocking loose on its woodruff key.  This looks to be because there is a shelf on the shaft which the washer is pressed up against.  Is this normal? Or should the rotor be gripped solid.  I am guessing that this loose rocking could make a lot of noise and lead to wear. 

[DAVE BRADY]

Hi,

Have you got the spacer/washer between the sprocket and the rotor?

Dave.

[Barnsey]

Yes.  The spacer is in there plus one shim, in order to align the primary sprocket. 

By chance, the Enfield Alternator arrived today.  It turns out that the Enfield one is around 3mm wider than the original, i.e. the former is about 17mm wide vs 14mm.  I might be tempted to try adding a shim between the sprocket and the rotor, so that the rotor stays in line with the new stator. That might fix this issue too.  I hope that there are enough threads on the shaft to be able to do this and still get the nut on. 
 
 It looks like the cover is deep enough to take the new alternator without issue.(Just cross everything).

[rhyatt]

The C15 has 2 drive side nut options and 2 lock tab options to hold the rotor hard against the shoulder on the crank.
1) is a nut that has a step on it which has a different ID to match it's own lock tab. From memory, this step goes down inside the magnetic rotor.
2) nut with no step and its own washer. Either way, the nut should hold the rotor firmly up to the crank step.
Ensure that the act of pushing the rotor onto the crank doesn't cause the woodruff key to ride up out of its slot.

[Barnsey]

Ahhh!  Now I had a dished washer without tab on my bike, so I replaced it with a tab washer.  Maybe this was a mistake. 

[DAVE BRADY]

Hi,

So you have the spacer that goes in the against the bearing and a shim for alignment. Then the sprocket and the spacer/washer and then the Rotor.
Spacer/washer indicated with arrow.

To help to stop the movement of the rotor on the shaft use some bearing fit and make sure the nut is done up really tight.

Dave.

[Barnsey]

Thanks!  Bearing Fit on order.  I'll hopefully continue on Friday when I am off work. 

[V500]

Thanks!  Bearing Fit on order.  I'll hopefully continue on Friday when I am off work. 

You shouldn't need to use Bearing Fit here as the components should tighten up when using the correct parts.
It'll be a sod to get off next time, too.

[Barnsey]

Point taken!

[JulianS]

If the rotor is rocking on the key I would try a new key which might be a better fit.

Are you certain the rotor is rocking on the key or is it the rotor centre rocking within the rotor body? The rotor centres do sometimes work loose in the rotor body and except for the later ones the pole pieces are not welded to the rotor centre it is just held together by the alloy casting metal. The results of a loose centre can be catastrophic.
Photo show a rotor I took from an A65 a few years ago, note the centre punch marks trying to stop the movement within the rotor.

[DAVE BRADY]

Hi,

If the rotor is a perfect fit on a perfect shaft it will probably need a puller to get it off anyway.  No different with bearing fit. It fills the space caused by wear through use and especially if it has not been tightened up properly over the years. A new key is a good idea but it will not compensate for wear in the rotor slot or the slot in the shaft or both.  Having to strip it down to cure a noise from the rotor is far more annoying than a bit more effort with a puller to get it off next time.
Next time should be long way off if done properly.  Also make sure you use a torque of 60 ft/lbs.

Dave.

[rhyatt]

I have just been checking my own C15 parts listing for this spacer mentioned above.
My own bike does not have this spacer and I therefore checked the BSA parts books - the earlier bikes do not show it and the later bikes DO show it.

[DAVE BRADY]

Hi,

The extract is from a '62 parts book. If Barnsey's C15 is earlier and never had one then something else is different.  However, in the first post it looks like the rotor is going on too far hence the washer is butting up against the step in the shaft. Fitting this spacer will solve this problem by bringing the rotor out a bit.

Dave.