Disintegrated rotor

A single phase high output alternator will do all you want. My Altas is so equipped and it is used extensively at night. 60/55 watt headlight, heated handlebar grips, electrical load matched easily.

Hello Gordon.....You are correct but the HI OP RM23 is quite hard to come by and is often very expensive. A three phase stator would work well for extra output but again you would need the 3 PH rec/regulator to go with it.

Back to the Mercury, if you did get a high output single phase you would still not be able to use the original single Zener system. So having to buy a reg/rect for Hi OP is about the same as such for the 3PH Your choice. BUT very often with these aged bikes....the real reason for low output is the magnestism in the rotor has faded away, so... a new rotor alone might bring you back to enough electricity. If the bike is hi days and holidays and you tend to 'nip down the bypass' quite a bit then the standard RM21 will suffice, if you want to potter in town with lights on half the time then you do need a few more amps.

Get in touch if you want any more info.

Al Osborn.

Hi Al, it's actually an RM21 on the Atlas but of course it is magneto ignition so no ignition drain. Seems perfectly adequate with headlight on all the time plus hot grips when it's a bit parky - not altogether a rare occurrence up here! Naturally I have a voltage regulator black box from AO Services (who else?). A big improvement on the rectifier/zener setup. Haven't heard of the famous rotor explosions for a good while now - implies an original and hence rather elderly alternator. Time for a complete new one I reckon. Dare I recommend AO Services once more?

Previously Gordon Johnston wrote:

Hi Al, it's actually an RM21 on the Atlas but of course it is magneto ignition so no ignition drain. Seems perfectly adequate with headlight on all the time plus hot grips when it's a bit parky - not altogether a rare occurrence up here! Naturally I have a voltage regulator black box from AO Services (who else?). A big improvement on the rectifier/zener setup. Haven't heard of the famous rotor explosions for a good while now - implies an original and hence rather elderly alternator. Time for a complete new one I reckon. Dare I recommend AO Services once more?

Hello Gordon, one might think you were a mate of mine! seriously though folks the cost of my alternators (with the name Lucas on them) are very prohibitive so I do not recomend you buy one from me. Mind you there is a lot cheaper ones from the far east with a short life I am told-your choice.

Now Gordon you are a naughty boy if you were running around with a 12V Atlas (all Atlas were 12V!) using a Zener/rectifier and a Magneto!! Don't do it, the lack of ignition drain when using the RM21 pushes the Zener over the top-pop! This did not happen when the Atlas came frm the factory as it had the three wire alternator (left over from 6V days) along with the 6V alternator switching to control the alternator output-hence charge current. So beware don't run RM 21 (or any two wire system) with Zener with Magneto, you have been warned.

By the way the older 74mm rotors with the number****106 are very prone to self distructing the older they get. The earlier (pre 1960 ish) 70mm rotors seem to last much better but due to age they still lose their magnetism.

Al Osborn

The 74mm rotors are quite handy bench magnets for keeping fiddly little screws from disappearing. Not much use for anything else.

Al, I think you missed this bit: "Naturally I have a voltage regulator black box from AO Services (who else?)."

As if I would use an RM21 with a Zener/rectifier. Well, hardly ever...

My 59 rotor still works fine and shows no sign of loose center and gives a good charge according to the meter. I would happily swap it for a new "welded" one except I dont think they exist (did they ever?).

Previously robert_tuck wrote:

My 59 rotor still works fine and shows no sign of loose center and gives a good charge according to the meter. I would happily swap it for a new "welded" one except I dont think they exist (did they ever?).

If your alternator works as well as you say, why would you be happy to swap it?

Hi John, It is a poor design, and it will fail --sometime, As its going to be belted round the IOM by my son , hopefully chasing me, a little insurance would be worth it. Are there any better rotors for the early alternators?.

A 1959 alternator is likely to be the old 74mm one. Best buy a complete new encapsulated one if you intend to change it. Of course the concours afficiondos would leap at the chance of a genuine 1959 alternator...

Previously robert_tuck wrote:

Hi John, It is a poor design, and it will fail --sometime, As its going to be belted round the IOM by my son , hopefully chasing me, a little insurance would be worth it. Are there any better rotors for the early alternators?.

Sorry Robert, can't accept your reasoning. If the alternator has lasted since 1959, the design can't be that bad. "If it ain't broke, don't fix it!".

Previously dominic_gomes wrote:

Hi John

That's what I thought - until mine exploded. It looked fine a week before it broke with no stress cracks as I was in the primary case checking the clutch spring tension. Admittedly I didn't take it off for a close exam.

OK Dominic, but where do you stop? Everything is going to wear out, or breakdown, eventually. If an alternator, made in 1959, is still functioning the design could not have been too bad. I ride a '54 Dominator, if I replaced everything that could be "Improved", it would no longer be the same machine.

I too have had an alternator explode (on a '71 Commando), but only because an "Expert" persuaded me it needed upgrading.

I have a healthy aversion to improvements , so my 99 is more orriginal than most. There are worries over components that would cause serious damage or safety issues if they fail.Alternators,old con rods ,slotted pistons and cracked sliders come to mind. I would have replaced the alternator already if I was convinced that the replacements were better designed.I bought new chains some years ago,only to be dissapointed with the quality , the old chains are back on and I have no idea of their age.The alternator on the 67 Atlas is past use now with a loose center.

Previously Gordon Johnston wrote:

A 1959 alternator is likely to be the old 74mm one. Best buy a complete new encapsulated one if you intend to change it. Of course the concours afficiondos would leap at the chance of a genuine 1959 alternator...

A slip of the finger/brain here Gordon, the older early 60s rotors are 70mm late 60s and now they are 74mm.

No 70mm parts, only second hand.

AO