Replace Alternator Rotor??

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WEM

WEM

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I had an electrical issue earlier this year with my 1974 Commando 850 which, with considerable help from forum members, was ultimately diagnosed as a bad stator. Sure enough, when I pulled the primary cover off to investigate, the stator epoxy? coating was cracked and looked like it was partially melted at one location. A new stator is definitely a must. However, my question now relates to the existing rotor. The rotor came off easily and looks good physically. No obvious signs of damage. The rotor will hang unsupported from a wrench handle so the magnets appear to be holding their magnetism as well. I'm wondering if it's false economy to re-use a 46 year rotor as opposed to spending $140.00 CAD for a new rotor, or if buying a new rotor is an unnecessary expense given that the old one seems fine?
 
I elected to buy a kit from here https://www.rexs-speedshop.com/product-category/classic-british-motorcycle-electrical/

Stator, rotor in Lucas boxes and R/R.
The stator holes were hit and miss as far as the ID and fitting over the primary cover studs but easily machined to do so.

(L.A.B and Kommando posted at the time (or might have been on BB.com when I asked) regarding this subject/parts source)
In hindsight I would have bought the "UK made" stator which might not be Lucas branded from here http://www.tms-motorcycles.co.uk/

The new rotor I got (Lucas box) looks to be a decent part and fits the crankshaft with a firm push fit though.

I think the catch is (based on plenty of OEM parts still working fine) are the modern replacements (only time will tell) as good as those decades old parts.
My thinking was to replace the lot as one unit and be done with it (I hope)
 
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From your description of the rotor holding a wrench, I would say the magnetism is sufficient.
If you are running a LED headlight, it would be certainly sufficient.

I vote to save $140 CAD.

Slick
 
I got Lucas branded rotor & stator with a Podtronics R/R from Walridge here in Canada for what I consider fair price and fairly quick delivery .....
 
46 years old? get a new one cost is around $100 US.. cheap insurance... they get loose and can hand grenade too...
 
Craig said:
I got Lucas branded rotor & stator with a Podtronics R/R from Walridge here in Canada for what I consider fair price and fairly quick delivery .....
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'Genuine Lucas' (sold in the green boxes, now red) is W E Wassell.

Electrical :: Charging System :: Alternator :: Lucas Alternator Stator 47244 RM24 - 3 phase, 12v

Genuine Lucas Alternator Stator 47244 RM24 12V 3 phase Lucas Equivalent Stator. 3 lead, 3 phase 14.5 amp stator. 9 PoleAmperes: 14 Three Phase No. of Leads: 3 OEM: 47244, LU47244
www.feked.com www.feked.com

Lucas Classic | Motorcycle

www.lucasclassicmotorcycle.com www.lucasclassicmotorcycle.com

Wassell Limited

www.totalbikebits.com www.totalbikebits.com
 
Don’t recall color of boxes , I do remember the toasted Wassel stator I was replacing was branded as Wassel , the new item from Walridge motors was branded as Lucas as was the rotor .... I had mined the Wassell stator and repaired broken wires , turned out to be a wasted afternoon in bike shed as I had no faith in my repair , used it most of this season with no troubles but found myself staying close to home , so ordered up the new kit and now at least in my mind I’m free to roam on the old bike .... no doubt I have old stator in new box , will take a look in the morning ...
 
I had one blow up and so did a friend so I always replace them now. Most of them are 45 years old. Some of them have been in engines that have already been worn out once or twice. If the core looks a bit loose then definitely throw it out. The new ones have more magnetism so they balance the battery at a lower RPM.
 
But are the new Rotors of the same quality as the old ones? for some time people that I know [and myself included] machine at least 005" off the rotor to avoid the rotor "growing" and damaging the stator.
 
It is very important to check rotor to stator clearance on the new stuff. Some I’ve had have been rather less than the specified clearance.

I also had an original rotor rub on the stator despite careful setting of the gap. I had tended to assume this was due to crank flex rather than rotor growth?

The last two I’ve done I’ve had the rotors machined to give a .020” clearance with no detectable down side.
 
How are the magnets "staked in" in the new rotors? I have long wondered if machining the rotors weakened the stacked in effect.

Slick
 
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I think this pic was taken by someone on here - apologies, I can’t remember who.

D84563C8-2AF7-4E2C-9DB1-97E670A640BB.jpeg

This is the ‘welded’ rotor - you can see it isn’t and never has been welded (that was a Lucas marketing term used after the cases of exploding rotors hit the press)

Casting the zinc alloy around the centre, magnets and keepers makes the whole thing secure (notice the ’barb’ on the keepers - that bit has evolved).

Machining the OD merely skims a little off the keepers and the zinc alloy casting material - the keepers (and therefore the magnets) are still well locked in to the casting after machining.

 
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texasSlick said:
How are the magnets "staked in" in the new rotors? I have long wondered if machining the rotors weakened the stacked in effect.

Slick
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What is the best Alternator Rotor available today (2019)

Are those rotors balanced, even if so a recheck could never hurt. I remember reading an article although can't recall the exact numbers where an ounce of out of balance out there on the end of the crank was (iirc) equivalent to 126 lbs at reline (4 cylinder bike) Once that early style center...
www.accessnorton.com www.accessnorton.com

"the centre core is in effect now a 1 piece spider with reverse dove tails to retain the tapered magnets , these are slotted in to the core prior to the pressure die casting process which then fully encapsulates the centre core and magnets in effect making it one piece construction , rotors are then CNC machined to internal / external tolerances"
 
gtiller said:
I think this pic was taken by someone on here - apologies, I can’t remember who.

View attachment 20310
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Lucas Alternator rotors

I am working on a 1970 750 Commando. First cleaning the parts and putting it back together, it came in boxes, then I will take it back apart to 'restore' it. That being said, it came with several alternator rotors and I remember reading that Lucas went to welded rotors sometime in the 70's. I...
www.accessnorton.com www.accessnorton.com
 
Thanks @L.A.B.

I knew I’d seen it here first - I’d saved it to my phone, as it was the best pic I’d seen to date, and I wasn’t sure what was going to happen to photobucket at the time!!!
 
Fast Eddie said:
I also had an original rotor rub on the stator despite careful setting of the gap. I had tended to assume this was due to crank flex rather than rotor growth?
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I had my original Lucas rotor self destruct and wipe out the entire primary. Primary chain, chaincase, timing scale, stator, and a bent gearbox mainshaft. I think that's called "catastrophic failure". I've always chalked it up to having not checked clearances well enough, but who knows. Crank flex? Maybe.
 
Crank flex is only a hypothesis. Fortunately I didn’t suffer a catastrophic failure like you.

I was super careful in ensuring a min 10 thou gap on my 850, but when I stripped it (for other reasons) the rotor had clearly been fouling and the stator was looking very unhappy as a result.

The engine was revved hard, hence my crank flex theory. Can’t think of anything else?
 
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