Britbike forum Forums Thread Like Summary - 6T Alternator

hi, just bought a 1957 6T that has no alternator fitted, would I be correct in thinking it should be a Lucas RM14 ?
Thanks, Jez

Yes, RM14 would be correct for 1957 models. However, as has been pointed out, it would be prudent to fit a later 12-volt unit such as an RM21. I own a 1957 6T and that is what I did.

No mate,

As Koan58 says, the RM designation is the entire alternator pack. For example Lucas did produce an RM 13/15 which was a blend of the 13 stator and the 15 rotor.

I think you should go to 12 volt with a rotor that fits your crankshaft, and a stator that matches it and doesn’t foul the primary case.

If Jon W says RM21 then I’d head in that direction.

Hi Jez,

Yes, you will need the later adapter ring, and if I remember correctly, you may have to file the keyway on the rotor to match. I did it back in 2006, so a little fuzzy on the details but all of that information is available on the web between this site and the Jockey Journal.

The unit engines fitted studs without an adapter. AFAIK all alternator primary cases need the adapter. I find that new "pattern" adapters are often to tight to the stator encapsulation, had one last week from my stash, but an original I had was fine. These pattern adapters are cast, with just the mounting bits machined, so you need to take a dremel(or file) to them to clear the encapsutation . I'd be very careful about removing any encapsulation, just clean up any mould flashing.

youre being kind .
it seems my understanding is whats lacking .
There are certain things I know from experience ,
And other things I have inferred from that experience .

i thought a later stator , open core or not ,
was a direct fit on the inner primary studs ,
when a pre-unit alternator inner cover had them there .

i have seen/see the adapter plate , just didnt know it was needed in all cases .
... i guess the older RM14 stator had a different mounting Center .

Hi Jez,

If you look at the No. 16, 1960-1962 B-range parts book, that will lay out what you will need. If you need a .pdf of that parts book, let me know, and I will email it to you?

That would be great if you could email it mate, it’s [email protected]
Many thanks for your help man

Hi Jez,

It's on the way.

You’ve chosen the lower output version of the RM24.

Is your bike using magneto or distributor?

If distributor, then it takes power from the generating system, a magneto does not.

This makes a difference to your electrical requirements.

I would have chosen the highest rated RM24 myself, as it leaves you with the largest margin for future eventualities (eg if a magneto fails and you wish to install EI , or simply want better lighting).

I think that you have not got the best value for your money.

Of course, if you only wish to sell a working machine, it only matters to the next owner. The bike will work just fine (especially if it uses a magneto).

Take special care of the gap all round between rotor and stator, (CRUCIAL!).
There is a tiny bit of freedom in the adapter mounting bolts to achieve this. I had to open the adapter holes a little to safely get there.

You can have a good enough charging system with the 10 A alternator.

I’m not saying more isn’t better, but 10 A will see you OK.

One thing I have noted on this thread is no real mention of a rectifier for the alternator, and a charging control such as a Zener diode.
In the past, I converted a generator and magneto pre unit rigid to a 60's era alternator with a a 60's era rectifier and a late 60's era Zener diode mounted in a finned heat sink. I then switched from magneto to distributor- all worked well and made a correct 12 volt electrical system.
The rectifier and Zener or modern day (hmphhh!) equivalents need to be considered and chosen to complete the charging system- and don't forget about a battery as well.
(Meanwhile, an hour later in the middle of my night, somewhere deep in the middle of a tropical jungle, a voice popped into my head.....)
"Hey Catt," the voice said.
"Yes?" I replied
"Deadstiffcatt, you also need to mention light bulbs! If he switches to an alternator and a 12 volt system, he may need to change those." said the voice.
"Ok, fine." I replied, "I'll edit the post to mention that. But what voice are you?" I inquired.
"It is I, Lucas, the Prince of Darkness!" the voice replied, "And remind him to make the proper sacrifice to ensure the system works!"
So with that, I got up, wrote this, and am now going back to bed, leaving you to think about zeners and rectifiers and bulbs and making sure it's all powerful enough that you can still mount an 8 track player on the bike's handlebars so you can blast Born To Be Wild as you cruise through the night. Cheers!

A bit earlier I said “ Adaptor ring is now fitted with the new flange bolts, all looks great so I’ve ordered the 10 amp 3 phase RM24 with matching rotor and regulator, I am getting excited lol”
So that takes care of the regulator which is 3 phase.
I realise if I don’t want any risk the magneto should be reconditioned but it seems good and I have other bikes I can ride if I need to fix it later.
The rest of the electrical circuit has already been converted and rewired to 12v!

My 6T has a single phase alternator, modern reg/rec plus a capacitor, Pazon IE fitted into the distributor, 60/55 Halogen headlight bulb, and a small alarm type 12v battery. The alternator runs it all without any problems, even if you disconnect the battery it will run with the capacitor, lights on, apart from ticking over, but if you speed the tickover to about 1200, all is well