Hi Ron
I did not think my comments would stir up such a hornets nest, but hopefully it helps push the rebuild forward.
A bit off the thread but regarding the clearance for the points on WD/D I was wondering if the design of the engine was unchanged from 1936/7. Around that time the Lucas Magdyno was redesigned. The earlier MN/1 Magdyno which was equipped with a 3 brush dynamo, the MN/1 was fitted with ring cam point set up, I suspect with the change to a simpler 2 brush dynamo set up with a CVC regulator there also a change to face cam MO/1 magneto. I have not got access to a MN/1 magneto to measure the difference between the two types, but it I sure the difference in overall length would make access to the points on WD/D much easier.
Also to be considered is the limitation of the height of the s.v. engine. One way round it would involve a major redesign of the crankcases, which would prove expensive, new tooling etc. so they stuck with the existing set up. Other manufacturers got around this problem by fitting an extended inlet manifold to move the carb. clear of the magdyno. There was not the same problem with the case of o.h.v. engines with the carb. being mounted higher. Note on the BSA the Magdyno is mounted higher relative to the chain case so the access to the points is not so difficult.
Back to the thread - Regarding the Miller Magdyno the operation of the Miller dynamo is set up differently to the Lucas EL3 dynamo. I have included notes taken from vincent.com website.
The Miller dynamo as originally wired, work differently then Lucas. Millers have three states of operation:
1. Output voltage is too low
2. Output voltage is about correct
3. Output voltage is excessively high.
In the first state the armature voltage is impressed directly across the field coil. Assuming that the cut-out relay is closed this would also put the battery across the field coil. If the voltage is low enough then the battery will be disconnected (as in start up conditions). This will maximize the current flowing through the field coil, implying a maximized magnetic field.
In the second state, where the system has equilibrated (sort of), the current through the field coil is decreased but not to zero. There is a resistor that is inserted in the field coil circuit. The resistor, which is the second winding on the field coil (wound non-inductively) is the mechanism for decreasing the field coil current.
The third state has no current flowing through the field coil. Without this current there can be little or no output voltage.
While this system sounds good, in practice it barely works. It is a fragile design that typically has been abandoned for the simplier Lucas type voltage control (states 1 and 3 only). I am not aware of any solid state regulators that will support the Miller regulation design,
I am no expert on electrics but I think it would be possible it could be easily set up to run as a direct lighting set in a manner similar to the Royal Baby/Flying Flea, where the dry battery in the headlamp was to power the parking light and tail light only when the engine was not running.
Is it not possible that the same battery could used to to excite the field coil, to enable the the dynamo to run the lighting load, but it would be necessary that once the dynamo starts charging it would be necessary to switch out the dry battery to avoid charging it, so may be a further cut out was installed elsewhere, maybe the headlight.
The use of Miller Headlight & Tail Light would indicate that the Miller Company supplied the electrical equipment. Another piece of the puzzle nearly solved - just finding the bits - Great.
Cheers SteveL.