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Jon W. Whitley
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#870534 01/30/22 6:00 pm
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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

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Jez #870543 01/30/22 6:36 pm
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Originally Posted by Jez
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
RM14 is the rotor. Any modern alternator will fit. I'm currently working on a 57 5T which has a 3-phase alternator fitted.

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Thanks, did you mean that is the correct Rotor?
Thanks for reply, Jez

Jez #870558 01/30/22 8:59 pm
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RM number identifies the entire alternator. Early ones used a smaller OD rotor (70mm). I wouldn't bother with these, even if you can find one.

Irrelevant for you, If you have no alternator at all, then you need a complete alternator (stator and rotor).

RM19 onward use a 74mm OD rotor. Only these versions are available new.

You may also need the mounting support.

If you want to keep the original 6V system, only the 3-wire RM19 is available AFAIK.

If you want to make a useable bike, as Stein says any of the RM21 to 24’s will fit, the 24 being the best value (in terms of power) for money.

koan58 #870560 01/30/22 9:12 pm
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Thanks for that, it will give me something to think about!

Jez #870586 01/31/22 12:23 am
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Originally Posted by Jez
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.


Jon W.


1957 6T Thunderbird 650
1968 T100R Daytona 500
1971 TR6R Tiger 650
1970 BSA A65F 650
1955 Tiger 100 - Project
1971 BSA A65 650 - Project
1972 Norton Commando 750 "Combat"


"Every time I listen to AC/DC, so do my neighbors"

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Originally Posted by Jon W. Whitley
Originally Posted by Jez
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.

Thanks, I’m a complete novice with electric, have I got it right in understanding that the RM21 is the stator? And I would need a 74mm rotor to go with that?
Would I need some kind of adapter to fit these?
Cheers, Jez

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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.


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Originally Posted by Jon W. Whitley
Originally Posted by Jez
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.

hi Jon, I’m thinking of fitting the RM24 10a stator, would that need the later adaptor ring or will the original work? Thanks

Jez #870810 02/02/22 1:52 am
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Originally Posted by Jez
Hi Jon, I’m thinking of fitting the RM24 10a stator, would that need the later adaptor ring or will the original work? Thanks

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.


Jon W.


1957 6T Thunderbird 650
1968 T100R Daytona 500
1971 TR6R Tiger 650
1970 BSA A65F 650
1955 Tiger 100 - Project
1971 BSA A65 650 - Project
1972 Norton Commando 750 "Combat"


"Every time I listen to AC/DC, so do my neighbors"

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Jez #870827 02/02/22 6:29 am
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I thought the RM24 was 3-phase, would need a different regulator.


"Gosh, it's not a 1/4 20, must be metric."

72 T120V cafe project "Mr. Jim"
72 T150V "Wotan"

DavidP #870840 02/02/22 10:59 am
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Originally Posted by DavidP
I thought the RM24 was 3-phase, would need a different regulator.

Yes, would need different regulator from what I understand

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Originally Posted by Jon W. Whitley
Originally Posted by Jez
Hi Jon, I’m thinking of fitting the RM24 10a stator, would that need the later adaptor ring or will the original work? Thanks

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.

Thanks Jon, I rang a company here in UK who specialise in these items and on an eBay advert say to ring them to confirm if it will fit, they said it will fit the standard mount but I’m sure that’s not right! Everything I have read says you need the later one

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Originally Posted by Jon W. Whitley
Originally Posted by Jez
Hi Jon, I’m thinking of fitting the RM24 10a stator, would that need the later adaptor ring or will the original work? Thanks

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.

I’ve found the later adaptor ring with the stator studs n nuts and the flanged bolts, will se how that mounts up and there are no problems before I order the Stator and Rotor etc, do you remember what spacers were needed Jon when you did yours for the rotor?

Jez #870906 02/02/22 9:46 pm
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if the inner cover is from a 6t it will have stator mount bosses and holes for studs
as this model came with an alternator
[Linked Image from i.ebayimg.com]
but in any case , if an adapter ring is needed , because its a different inner cover .
the fixing hole pattern for mounting any and all of the RM stators ... is the same .
this is the one thing on all stators that did not change .
[Linked Image from tigercubandterrier.com] .

when rotor size changed from 70 to 74 mm ... the stator fixing hole pattern remained the same

cant guarantee that the outer cover is wide enough to fit an rm24 ?
... but mounting a later stator and rotor shouldn't be much of a problem .
stators , from about 1967 , have encapsulated coils .( an the width can vary a little )
you may have to carefully grind away some of the plastic to get a good fit ? ( or you may not )

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Originally Posted by quinten
if the inner cover is from a 6t it will have stator mount bosses and holes for studs
as this model came with an alternator
[Linked Image from i.ebayimg.com]
but in any case , if an adapter ring is needed , because its a different inner cover .
the fixing hole pattern for mounting any and all of the RM stators ... is the same .
this is the one thing on all stators that did not change .
[Linked Image from tigercubandterrier.com] .

when rotor size changed from 70 to 74 mm ... the stator fixing hole pattern remained the same

cant guarantee that the outer cover is wide enough to fit an rm24 ?
... but mounting a later stator and rotor shouldn't be much of a problem .
stators , from about 1967 , have encapsulated coils .( an the width can vary a little )
you may have to carefully grind away some of the plastic to get a good fit ? ( or you may not )

Thanks for that, just had my outer cover off and mine is tha same as the photo, I’ve sent off for the stator mount that fits but allows a later Stator that is encapsulated to be mounted, like you say hopefully with no fouling! And of course with the 74mm rotor common to all the Stators from RM21 upwards?

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if the inner cover for a 6T has the 3 studs and wire exit hole ... these are for Direct stator mounting ,
you will not need the "adapter ring ."
this inner cover came paired with the fatter outer-cover ( that had room for the stator )
( used in 57 , on only 5T And 6T )

( back in the day more to most pre-units ran an external generator and Magneto
the inner cover is simpler as it has no stator Mount studs or stator-wire exit hole ... and they were paired with
a lower volume outer cover )

you can see the two different inner covers and 2 different outer covers
Pictured and listed in the "57" parts book .
Figure # 24 , primary chain case(s) , page 77

its the other pre-unit engines , that originally I didn't come with alternators that will
need the stator-ring , and a replacement wider cover , if/when an alternator is to be fitted .

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Originally Posted by quinten
if the inner cover for a 6T has the 3 studs and wire exit hole ... these are for Direct stator mounting ,
you will not need the "adapter ring ."
this inner cover came paired with the fatter outer-cover ( that had room for the stator )
( used in 57 , on only 5T And 6T )

( back in the day more to most pre-units ran an external generator and Magneto
the inner cover is simpler as it has no stator Mount studs or stator-wire exit hole ... and they were paired with
a lower volume outer cover )

you can see the two different inner covers and 2 different outer covers
Pictured and listed in the "57" parts book .
Figure # 24 , primary chain case(s) , page 77

its the other pre-unit engines , that originally I didn't come with alternators that will
need the stator-ring , and a replacement wider cover , if/when an alternator is to be fitted .

I probably didn’t explain it right, I’ve ordered the direct stator mounting that will mount the later encapsulated Stator, rather than the original mount that had the early hexagonal stator with the exposed coils like in the diagram

quinten #870930 02/03/22 1:02 am
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Originally Posted by quinten
if the inner cover for a 6T has the 3 studs and wire exit hole ... these are for Direct stator mounting,
you will not need the "adapter ring ."

it's the other pre-unit engines, that originally I didn't come with alternators that will
need the stator-ring, and a replacement wider cover, if/when an alternator is to be fitted.


Negative. If one wants to fit an RM19 and later rotor and stator to their 1953 through 1959 5T or 6T, they will need the adaptor ring.

As far as the "other" magneto and generator engines are concerned, if they are 1959 or earlier, they will need inner and outer alternator cases to accept the adaptor ring. Mag/Gen inners have no provision for fitting anything like an adaptor ring, let alone, a stator. And, the non-alternator inner or outer cases won't match up to alternator inner and outer cases..rigid or swingarm type.


Jon W.


1957 6T Thunderbird 650
1968 T100R Daytona 500
1971 TR6R Tiger 650
1970 BSA A65F 650
1955 Tiger 100 - Project
1971 BSA A65 650 - Project
1972 Norton Commando 750 "Combat"


"Every time I listen to AC/DC, so do my neighbors"

Jez #870935 02/03/22 1:23 am
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Originally Posted by Jez
I’ve found the later adaptor ring with the stator studs n nuts and the flanged bolts, will see how that mounts up and there are no problems before I order the Stator and Rotor, etc, do you remember what spacers were needed Jon when you did yours for the rotor?

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?


Jon W.


1957 6T Thunderbird 650
1968 T100R Daytona 500
1971 TR6R Tiger 650
1970 BSA A65F 650
1955 Tiger 100 - Project
1971 BSA A65 650 - Project
1972 Norton Commando 750 "Combat"


"Every time I listen to AC/DC, so do my neighbors"

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Quote
I probably didn’t explain it right, I’ve ordered the direct stator mounting that will mount the later encapsulated Stator, rather than the original mount that had the early hexagonal stator with the exposed coils like in the diagram

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 .

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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.

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Originally Posted by Jon W. Whitley
Originally Posted by Jez
I’ve found the later adaptor ring with the stator studs n nuts and the flanged bolts, will see how that mounts up and there are no problems before I order the Stator and Rotor, etc, do you remember what spacers were needed Jon when you did yours for the rotor?

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

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Jez #871036 02/04/22 12:37 am
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Originally Posted by Jez
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.


Jon W.


1957 6T Thunderbird 650
1968 T100R Daytona 500
1971 TR6R Tiger 650
1970 BSA A65F 650
1955 Tiger 100 - Project
1971 BSA A65 650 - Project
1972 Norton Commando 750 "Combat"


"Every time I listen to AC/DC, so do my neighbors"

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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

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