Kokusan Alternator on my Commando

For the last 30 years or so my Commando electrics have been powered by a Kokusan 19Amp alternator, as fitted to the air-cooled rotaries. The stator is spigoted and screwed to a machined adapter plate which bolts to the existing stator mounting The original stator mounting studs were replaced with bolts, the heads being thinned to clear the stator (c's'k screws would have been better but, I didn’t have any). The rotor is screwed to an adapter which replaces the original lucas rotor on the crankshaft, using the existing sleeve nut and key. I made this adapter from a lucas rotor center that I removed from an old rotor (it was already loose in the rotor so no harm done) to which I welded a spacer and flange to mount the Kokusan rotor. The ignition timing plate had to be removed from the outer case to provide clearance for the rotor owing to the space being a bit tight!. All machining I did on a very nice and well equipped 9" swing South Bend cabinet mounted lathe (I now have a Boxford ME10A which is a more modern version of it). The voltage control unit came from the same source as the alternator. I've included a couple of photos showing the stator and rotor loosely assembled.
I didn't have to do it, but it was free (an unwanted old development alternator) so why not?
I thought I should post this in case it gives anyone else a similar idea.

Nice. What, if any, are the advantages/drawbacks from the conversion, versus the stock Lucas and aftermarket replacements?

Ken

lcrken said:

Nice. What, if any, are the advantages/drawbacks from the conversion, versus the stock Lucas and aftermarket replacements?

Ken

Click to expand...

I have no experience with aftermarket replacements so can’t comment on those.

Advantages over Lucas - greater clearance between rotor and stator. Plenty of power at low revs for extra equipment eg more lights, heated clothing/gloves/boots. Uses a proper 3 phase regulator - No zenor diodes. When I did the installation I don’t think there were any alternatives to the Lucas items.

Disadvantages- the regulator used on the rotaries had a major design flaw in that if battery is disconnected while running the engine the voltage regulator will be damaged. Designed for negative earth so bear that in mind. Norton claimed that the regulator was specially made for the rotary bike and nothing else would fit but I think that applies to the bike as any 3 phase 19A plus regulator should work. Needs special mounting plates/adaptors making. The ignition timing plate is in the way and must be removed so an alternative needs to be made and fitted.

I think it took me a couple of weekends to measure everything, design and make the parts and fit it. The materials I had in stock. HE30T6 aluminium and 50/55 ton steel for the rotor adapter. Or thereabouts. Fasteners to suit. Now that alternatives exist you have to like making things to do it, but it was satisfying to do something nobody else had done.

hybridracer said:

I have no experience with aftermarket replacements so can’t comment on those.

Advantages over Lucas - greater clearance between rotor and stator. Plenty of power at low revs for extra equipment eg more lights, heated clothing/gloves/boots. Uses a proper 3 phase regulator - No zenor diodes. When I did the installation I don’t think there were any alternatives to the Lucas items.

Disadvantages- the regulator used on the rotaries had a major design flaw in that if battery is disconnected while running the engine the voltage regulator will be damaged. Designed for negative earth so bear that in mind. Norton claimed that the regulator was specially made for the rotary bike and nothing else would fit but I think that applies to the bike as any 3 phase 19A plus regulator should work. Needs special mounting plates/adaptors making. The ignition timing plate is in the way and must be removed so an alternative needs to be made and fitted.

I think it took me a couple of weekends to measure everything, design and make the parts and fit it. The materials I had in stock. HE30T6 aluminium and 50/55 ton steel for the rotor adapter. Or thereabouts. Fasteners to suit. Now that alternatives exist you have to like making things to do it, but it was satisfying to do something nobody else had done.

Click to expand...

Those are some big advantages there. A new regulator rectifier would solve those disadvantages. I am playing with a similar design using a modern japanese alternator design that can run in oil as I have a MK3.