Re: Loose alternator rotor centre.

Started by Bess, 07 Apr, 2023, 16:45

Previous topic - Next topic
Print
Go Down Pages1 2 3
User actions

Bess

07 Apr, 2023, 16:45
Hi,
    Thought I would share this, I looked on the forum and cannot find anyone else having the issue.

I recently put a rotor on a A65 before the stator, turned the rotor by hand to check if there was any play in the key and keyway. The rotor turned a few degrees either way on its centre. I had another spare rotor which I checked and that was the same, so a new rotor on its way (expensive bit of metal). If the rotor is off the bike clamping the rotor centre in a vice and turning the rotor works, as the centre is bigger than the rotor.

I searched the internet and found a Triumph service sheet which addresses the issue and a few horror stories of rotors coming apart. I also read of a bodge of putting large star washers either side of the rotor locking the centre to the rotor, which maybe worth looking for.

I didn't have a tell-tale knock as described on the service sheet, although another clue could be the strobe timing not as expected.

Best wishes...

Spaceman

#1
07 Apr, 2023, 17:21
From pics of this type of rotor, it looks as though the centre with the key way cut in it is probably a press fit in the body of the rotor. If the original rotor is now scrap, it would be interesting to see if the centre can be pressed out. If it can, I would have thought a coating of suitable Loctite retaining fluid would then hold it firmly in position once the centre was pressed back in?

Bess

#2
07 Apr, 2023, 18:12
Hi Spaceman,
                    I have investigated and the centre cannot be pressed out, the zinc is cast on and the centre is made from hexagon bar. I believe the later rotors have the centres welded to the arms connected to the magnetic section which stops the possibility of loosening.

I guess you could melt all of the zinc off, weld the arms to the hexagon then the magnetic section on the arm ends. Wouldn't be something I'm going do.

Best wishes...

Spaceman

#3
07 Apr, 2023, 19:45
I assume this pic shows the construction and the hexagonal bar? At face value, I would be surprised that the centre could come loose or is the assumption that the magnets are starting to break up? In looking into this, I read a suggestion that the welded centre was just a marketing ploy by Lucas and didn't actually exist?

Bess

#4
07 Apr, 2023, 19:59 Last Edit: 07 Apr, 2023, 20:01 by Bess
Hi,

Worth a look at a loose centre, both of mine are exactly the same:

    https://www.youtube.com/watch?v=Ge9NUoBz3W4

Advertised as welded rotor, note the part number has changed:

https://www.feked.com/alternator-rotor-magnet-genuine-lucas-rm20-rotor-lu-54202299.html


Best wishes...

Mike Farmer

#5
07 Apr, 2023, 20:42
 :) :) :) :)

I used a large punch and 'piened'? mine into the join and stopped the movement. Seems OK, Ill let you know.

Mike 8) 8) 8) 8)

Bess

#6
11 Apr, 2023, 08:21
Hi Mike,
             Did you hear the rotor knocking when the bike was running? Or did you notice an issue when building the engine?

Best wishes...

ChrisG

#7
12 Apr, 2023, 12:07
Dave Smith mentions in his RR Unit single manual that 'The rotor has one main failing which is that the steel centre come loose in the surrounding magnets and aluminium..'
However, it can be 'resuscitated' but will need a lathe and some epoxy resin and turned to remove the rotor centre.

If you want to take this route and haven't got the manual, PM me with your address and I'll send you the full details

JulianS

#8
12 Apr, 2023, 15:51
Below are some photos of a 1970 rotor, casting number 54212006. I thought it was scrap so melted off the casting material to see what was beneath.

First photo shows the heavy punching to stop the rocking.

Second photo same rotor same side with most of the casting material removed. When heating it to melt off the casting some oil seeped out from between casting material ane the pole pieces and the casting and the centre.

Third photo show reverse side, note the steel brace between centre and 4 of the pole pieces.

Last one shows the rotor and a shining mark where a magnet has been rocking on the hexagonal centre.

Bess

#9
12 Apr, 2023, 17:37
Hi Editor,
              Thanks for your offer, I now feel Julian finding oil in the rotor internals would make me wary of any repair using epoxy. Coincidently the new rotor arrived in the post today, need some good weather to fit it.

Best wishes...

Mike Farmer

#10
12 Apr, 2023, 22:18
 :) :) :) :)

Hi Bess.

I found it whilst doing rebuild. So no idea what my success or otherwise may be. If I have to purchase a new one where would it be a sound idea to try. I'm in no rush and in truth I'm never going to ride it just would like to get it right.

Mike 8) 8) 8) 8)

Mike Farmer

#11
12 Apr, 2023, 22:24
 :) :) :) :)

I've just looked at the pics and wonder why the cover is actually there. Is it just to keep it dry or is it to stop rotation
, or???

Mike 8) 8) 8) 8)

Mike Farmer

#12
12 Apr, 2023, 22:32
 :) :) :) :)

To continue from wrongly pressed button. If punching is unsuccessful I might try drilling in a couple of places and using roll pins.

Mike 8) 8) 8) 8)

JulianS

#13
13 Apr, 2023, 09:08
Some more photos of the rotor bits. My concerns would be if the magnets and laminated pole pieces moved when the rotor heats in use.

Bess

#14
13 Apr, 2023, 10:01
Hi Mike,
            I believe magnets are brittle and if drilled for a roll pin may cause more problems.

Best wishes...
Print
Go Up Pages1 2 3
User actions