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Wipac alternator rotor


All I have read about the Wipac alternator rotor states that the bore of the rotor is 1" diameter as opposed the the 3/4" bore of the Lucas rotor.  Most recently mentioned in the "Alternator Help!"  thread that is presently running.

My Navigator crank shaft measures 31/32" (0.968") diameter, I've also measured a Jubilee crank that is the same.  The rotor is a good fit on the crank, as it should be. 

I wondering if there ever was more than on size of Wipac rotor bore, or is the 1" wrongly stated, or is there some other explanation?

I'm running my Navigator with a Lucas encapsulated stator and a Wipac rotor, seems to work well enough.

I did consider boring a Lucas rotor to fit the shaft, anyone tried that?  I wonder if the construction of the Lucas rotor would allow this?  If I can find a tired rotor I am going to give it a try before modifying a good 'un.






Not wanting to live up to the title above, but...

Electra uses a Wipac rotor with a larger bore than Jubilee and Navigator.

Wipac alternators were fitted to many types of m/c and other small engines so I'd be amazed if there were only two bore sizes for Wipac rotors.



The Wipac rotor is known as 1" bore, or is this 31/32 or is this 24.6mm? Yes Wipac were fitted to many other machines but in all these years with Norton NO ONE has mentioned another size for Wipac inside. There is only the ONE size (as far as we know) Even if there was a 3/4-19mm version it would be 50yrs old (low magnetism).  I have looked at the Lucas rotor, as soon as you look at boring it out stop and think how it is made, how much metal will be left, how crucial is it to be safe? If it comes apart in service, you will loose charge, you will also seize your engine at speed and if you are lucky you might just fall off. Another small point as the Wipac is a few mm smaller than the Lucas then the Lucas rotor inside the Wipac would interfere. If you can get a batch of said Lucas rotors bored out with a 10 year guarantee I will have a box full.


..lists the complete alternator with a Norton number 24865, and another presumably Wipac number G1697. 

The bare rotor is only listed with a Norton #, S0734.

Not sure how this helps, but now you know... 


The crank dimensions are THE SAME on all 3 models, so the magnetic rotor is ALSO the same on all 3 models (Jubilee, Navigator & Electra). However, the stator (coils) are different for the Electra (it is wired 2 coils + 4 coils), as opposed to the Navi & Jubilee (3coils + 3coils).

The crank dimensions are 0.9670" to 0.9675" - which, as you can all see, is a whisker less than 1"

My details are in RoadHolder under "Tech Advice"


So sorry. The Wipac rotor of the Electra is the same as measured by John.

Just measured both.

Thank you to all for reminding me not post rubbish.



Still haven't found a tired Lucas alternator rotor to have a look at its insides.  I have found out that construction of the rotor changed over the years so it will not be so easy to determine if its worth doing.

I also found an article in Roadholder describing the fitting of an alternator to a heavyweight twin, this involved boring the rotor to suit the crankshaft.  Couldn't find out if there has been any feedback giving an indication as to the success or otherwise of the work.

I am making some significant modifications to my Navigator crank shaft.  While I'm making other modifications to it, I'm considering maching the end of the shaft to suit a Lucas 3/4" bore rotor.  I cannot see this being a problem, the 3/4" bore rotor is okay on the likes of Triumph and BSA's.  I assume Commando's also used the same?


Michael, would rather not share at the moment, I want to see if my ideas work first.  If they do then happy to share.  If things go wrong then I'll just keep quiet!

I'm not a slave to originality and some of the modifications, engine and gearbox, are quite involved, no going back if it goes wrong!  Having said that most parts will return to original if necessary and I make sure I have spares for those that will not.

I think it safe to say that the lightweights had very little development after being brought  to the market, probably for financial reasons. Does anyone wonder how the bikes may have developed if Norton/AMC did develop the bikes?



John.  Sounds like need the dimensions of the inner rotor boss (with the bore and keyway, normally concealed within the moulded alloy outer)

If so let me know and I,ll attach them to this post or send directly to you. I have an intact inner from one which exploded on my Commando. Latest 14.5amp 3 phase alternator but I believe the rotors are the same.

Not welded by the way, all held together by the alloy


ALL the Lucas rotors are 19mm bore. Prior to 1960 (or there about) the outside was 70mm. The later ones are all 74mm. 54212006 rotor was prone to coming apart, and perhaps earlier ones.

54201143, 54202298,  54202299,  54212298.  These are all thought to be Hot riveted, hence NOT prone to flying apart.  All Lucas rotors are magnetically identical. 3 phase is 9 pole pieces (not just 3 wires)


Lucas rotor bores are 3/4" diameter, if they were 19mm they wouldn't fit!

Lucas recommended the shaft the rotor fits on to be 0.7520/0.7505", 19mm = 0.748"

Apologies for being a pedant


Correct John, no chance of pressing that on easily with basic hand tools. I would also like to see evidence of why someone thinks they are hot riveted as well. The rotor centre I have in front of me from a 54202299 rotor which DID fly apart, has no hot riveting or weld marks whatsoever….  Held together within the alloy as stated unless someone has more info on this. A post some time ago on another forum where someone stripped a rotor down to the bare centre came to the same conclusion.


I did say I 'thought' they were hot riveted. But the snag here is that we don't find out until it's too late. I have some reasonable conversant alternator numbering but NOT a definitive listing. Does any one else have info.


Why is this thread still running?

The Lucas Rotor, as stated above, has a 3/4" bore.

The Wipac Rotor is a whisker under 1" - there is no way that you are going to bore out a Lucas Rotor to suit an Electra crank (whose dimensions are 0.9670" to 0.9675") without compromising it. Early Lucas Rotors were known to fly apart even without assistance!

In addition, the Wipac Rotors are more robust (they never flew apart, or got loose on the central spacer) - and keep their magnetism better as well. If you do not have an alternator at all on your Electra, try & find one on eBay. If you find the stator coils are damaged/burnt out/shorting to ground/whatever - then replace it with a 2-wire 12 Volt stator from Lucas. Wassell import them at present (from India?). They are well made & good value.

The airgap will be slightly larger than with the original Wipac Stator, so Power produced will be lower - but with modern LED headlight bulbs, that should not be an issue.

I would also suggest you use a modern Rectifier/Regulator, rather than the mechanical curiosity under your seat - hence I suggest a 2-wire stator. Good Luck


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