Miller or BTH

[Andy B]

I'm lucky to be in a position to have the original Miller setup for my 37 A, but I also have a BTH from an earlier model. Question, what was the better setup? I'm not a stickler for originality, the Miller was on the bike when it left the factory but if the BTH is the better unit I'll use that.
Both need full resto!

 

[Marvel]

Nice position to be in.

 

[Simon Dinsdale]

To fit a BTH unit the factory had to grind a small area at the back of the crankcase where the mag dyno butted up to the crankcase. This was only done on engines that used BTH so your crankcases may not have this. If so then would you be willing to remove metal from your crankcases to fit the BTH mag/dyno?
This is my bike showing a BTH unit fitted showing the area where the cases are relieved:

It was always considered that the BTH magnetos were of a better build quality to Lucas and others. Today that can be dismissed though as its down to the ability and quality of the person rebuilding the mag and rewinding the armature etc.
The BTH dynamo only generates a max of 24 W at 6V and as its a permanent magnet dynamo so there is no voltage control and so a basic charge control is done via a charge resistor on the headlight switch.
The Miller dynamo is I believe is 36W and a more standard field coil and so can be regulated via a modern electronic unit. So you will have more electricity for lighting with the Miller unit.

 

[Andy B]

To fit a BTH unit the factory had to grind a small area at the back of the crankcase where the mag dyno butted up to the crankcase. This was only done on engines that used BTH so your crankcases may not have this. If so then would you be willing to remove metal from your crankcases to fit the BTH mag/dyno?
This is my bike showing a BTH unit fitted showing the area where the cases are relieved:
View attachment 45251


It was always considered that the BTH magnetos were of a better build quality to Lucas and others. Today that can be dismissed though as its down to the ability and quality of the person rebuilding the mag and rewinding the armature etc.
The BTH dynamo only generates a max of 24 W at 6V and as its a permanent magnet dynamo so there is no voltage control and so a basic charge control is done via a charge resistor on the headlight switch.
The Miller dynamo is I believe is 36W and a more standard field coil and so can be regulated via a modern electronic unit. So you will have more electricity for lighting with the Miller unit.

Thanks Simon, I will restore both and hopefully the Miller is serviceable, I'm sure someone will want the BTH.

 

[greg brillus]

Andy, I sent the main parts of the Miller I did for Stephen to Chris Zoch.......On the north side of Sydney........He re wound the armature, replaced the damaged slip ring, new condenser and re magnetized the housing........The rest i did myself including the full overhaul of the Dynamo.......It put out a lovely blue spark at a relatively low turning speed and the bike was an easy starter.......I installed a 6 volt modern regulator inside the front upper corner of the tool box neatly out of the way.........all worked a treat.

 

[Andy B]

Andy, I sent the main parts of the Miller I did for Stephen to Chris Zoch.......On the north side of Sydney........He re wound the armature, replaced the damaged slip ring, new condenser and re magnetized the housing........The rest i did myself including the full overhaul of the Dynamo.......It put out a lovely blue spark at a relatively low turning speed and the bike was an easy starter.......I installed a 6 volt modern regulator inside the front upper corner of the tool box neatly out of the way.........all worked a treat.

Thanks Greg, I'll get Chris's details and give him a call, I'm on a roll t the moment.