Having replaced my Electrex ign/lighting set up with an electronic ign and alternator with combined regulator/rectifier I have the following problem. The ignition is fine but on an initial test putting a multimeter on the battery terminals I find no increase in voltage with the engine running/revved. I already had a decent rotor with good magnets off an RM21 Alternator and so bought a new RM20 stator which I believed to be compatible. When I fitted the stator, as a quick test I put a bulb across the 2 output terminals of the alternator. The bulb lit when I started the bike and the bulb glowed brighter and brighter when I revved the bike seemingly ready to blow. So ok. I looked in Lucas testing papers and read that in the early 60's the outside diameter of the Rotor was increased from 70mm to 74mm. I looked at my alternator and saw a larger gap between stator and rotor than expected and measured the rotor at 70mm. The same papers said the gap should be a minimum 10 thou but no maximum. I now looked for a new rotor to replace it and all for sale said they were a direct replacement for all alternators from late 50's to early 70's and measured 74mm! So how would a 74mm replacement rotor fit the original stator which had my 70mm rotor fitted to it? Do you think the now 2mm gap is ok and the problem lies with the Wassel reg/rec which I have had lots of trouble with on previous bikes? Sorry for the length of this Post but I wanted to include as much info as possible.
John.
A 70mm rotor will not work properly in the stators designed for 74 mm. I dont think anyone is making new 70mm rotors.