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Navigator alternator replacement

Submitted by nicholas_clarke on Mon, 22/04/2019
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Light Twins

I know this is an issue much discussed in the past but I can't quite pin down the discussion thread that gives the definitive answer.  My old Wipac alternator has finally died and having already converted the bike to 12v electrics I want to replace it with a modern 12v stator and a new rotor.   From various threads I see that the Lucas RM21 stators is widely recommended as a readily available replacement but these require a 74mm external diameter rotor.   My question is does the 74mm rotor have the right internal diameter and key way to fit on a Navigator's crankshaft?    

Thanks in anticipation!

Nick        

Submitted by alan_osborn on Mon, 22/04/2019

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Easy answer NO. The Jubilee, Navi, and Electra crank shafts are all 1" so the Lucas type 74mm rotor will not fit ie it is made for a 3/4" crank, no you can't bore it out either, there would be little metal left to be safe. The Wipac rotors do seem to go on for ever, and you can get them re-magnetised if their is any doubt. The RM21 stator will give a bit bigger gap to the rotor but this is acceptable.

Submitted by robert_tuck on Tue, 23/04/2019

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I don't know if the lightweight stator studs are the same size as the Dommies ,if they are then the RM21 stator is not a straightforward fit. A rotor spacer,sleeves,stepped studs or rethreading the mountings will be needed. Perhaps someone with a lathe and the interest in keeping us going would step in and supply members directly, Anna ??. You've got my order ,3 stepped studs for a dommy please!!.

Submitted by nicholas_clarke on Tue, 23/04/2019

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Thanks Alan,really helpful as ever!    I am using your excellent modern rectifier / voltage regulator, should I use the three or two wire RM21 or doesnt it matter?   I am guessing the 2 wire is fine?    Thanks for the heads up Robert - can anyone advise over stator studs?   

Nick

Submitted by nicholas_clarke on Mon, 06/05/2019

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Well after a busy Easter I have finally got round to solving the Navigator's electrical problems.   A careful check through the charging system proved that the original, ancient and very battered Wipac 6v alternator had finally died and the modern rectifier / regulator had failed (perhaps as a result) so I bit the bullet and bought a modern Lucas rectifier / regulator and a two wire RM21 and fitted both which has solved the problem.   As Alan points out the original Wipac rotor is slightly undersize giving a circa 12 thou gap but the ammeter is showing a healthy charge rate so it isn't an issue.    As for the studs being undersized for the holes they are so I sourced a length of thin copper tube from my local model aircraft shop for £1.25 and cut three spacers which fitted perfectly so no need for stepped studs!    With the higher output of what is now a late 60s 12v system I am going to experiment with higher wattage headlight bulbs (60/55W H4 Halogen pre focus?) so perhaps I will actually be able to see at night which will be a revelation!   Thanks for the advise - it really helped sort this quickly.   Nick           

Hi Robert, sadly I've used all the remaining brass tube (not copper as I stated) tube on another job but it is readily available either from Hobby Hangar in Yeovil (01935 422400) or perhaps quicker if you don't live near from ebay for a couple of pounds.   I searched using K&S Copper tube #8133 5/16 x .014 and quickly found some for £4.25 from a dealer near Drifield in Yorkshire called flying-tigercat / Cottage-Craft-RMCE.   I have attached a photo of the packaging which luckily I hadn't thrown out!   Good luck - I found it was a perfect fit over the studs on my Navigator and into the holes on the Lucas stator and centralised it over the rotor without any more fettling.   I hope that solves your problem!    Nick   

Attachments
Copper tube for alternator.JPG

Submitted by philip_hannam on Mon, 06/05/2019

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Nick........think about changing all those filament bulbs for the latest LED versions. Paul Goff offers such replacements. This way any loss of Watts due to the mismatch of alternator chunks will easily be negated by the much lower total power drain when everything electric is being used.

 



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