Classic cars forum & vehicle restoration.

peter scott · Joined: 18 Dec 2007 Posts: 7119 Location: Edinburgh

I confess that I don't understand the earthed third brush either. The cut-out is quite normal and has its shunt coil across the dynamo output and a series coil just to add to the pull current and prevent the contacts from chattering at lower voltages.

I suspect that the shunt on the dynamo is the field coil although diagramitically it is shown external to the casing. See if you can trace the connections to it and you might discover what and where it is. With the switch in the M position it should be possible to measure the resistance of the shunt. There might be more than one field winding and this shunt might be adding or opposing the magnetism as selected by the D or M switch positions.

Operating it in the car should tell you what's what.

HTH

Peter
_________________
http://www.nostalgiatech.co.uk
1939 SS Jaguar 2 1/2 litre saloon

jp928 · Joined: 07 Jun 2016 Posts: 249 Location: Australia

Back to the starter - on further inspection there are 4 screws holding the mounting face onto the body. On removal it was very easy to rotate the plate 90d, without any electrics being involved, and the connections are now safe and in the same position as the other examples.
Another win, only a few 100 more to go...

thanks
jp

jp928 · Joined: 07 Jun 2016 Posts: 249 Location: Australia

Next query - the headlight bulb holder seems incomplete - am I missing some sort of spring loaded electrical contact here. The unit is a Lucas R40M.
Whats the std wattage one would use for a 6V bulb here ?
tks
jp

goneps · Posted: Wed Jul 06, 2016 4:27 am Post subject:

Can't help with the bulb holder I'm afraid, but I'd guess the wattage would be 24/24W—certainly no more. That's 8 amps just for the headlamps, and the dynamo may only have a maximum output around 10-12A.

In my experience the majority of those who complain bitterly about 6V lighting are the ones who put in bulbs of higher wattage than the dynamo can support.

Richard

47Jag · Posted: Wed Jul 06, 2016 4:31 pm Post subject:

PJ,

I think the part you are looking for is a plastic contact holder that were used in a lot of Lucas lamps. They come in single and double contact and have the two flat sides to keep them in position on the reflector. I think the get centre punched in the side paso that they don't fall out. I found these which may be use as substitute. Item 153 or 153s.
https://www.completeautomobilist.com/search?query=Bulb+holder

Art

MVPeters · Joined: 28 Aug 2008 Posts: 822 Location: Northern MA, USA

That's a bulb holder for a single contact bayonet bulb, a BA15, BA15S or SBC.
Note there are 3 detents for the bayonet - they are to adjust the focus.
If you can find any yellow-lens rear light unit off a Mini or MGB or hundreds of others, you can pull out the spring-loaded bit from the front & insert it in your reflector. Even the 21W bulb will work, though it may not be optimum.
The correct bulb would be a bit larger & more global in shape.
(Edited to add - 12V bulbs will be dim! but you get the idea).
_________________
Mike - MVPeters at comcast.net
2002 MINI Cooper 'S'

jp928 · Joined: 07 Jun 2016 Posts: 249 Location: Australia

Excellent, thanks guys! Will look for such an item down here, or order from UK next time I need something else from there. Another problem solved!

jp

jp928 · Joined: 07 Jun 2016 Posts: 249 Location: Australia

As a final note on the starter - having got some wiring in place and a battery ready. I wired an isolation switch on the main +12V feed, with live side to the new loom, and heavy lead to the starter. Starter switch is in the negative heavy lead as in the wiring diagram. So I thought before I chance any smoke escaping I would check some stuff - there was full battery volts across the isolator - that cant be right? The wiring diverges a bit from the diagram because the internally grounded 3rd brush requires that the dynamo body be earthed, which means the car is now neg earth. After a bit of chasing I found the neg pole of the starter was shorted to the starter body. Starter motor out again. There was a fibre washer evident INSIDE the body on the neg pole bolt isolating the internal connections....but not on the outside. When I pulled the retaining nut and washers off, there was a steel washer at the bottom. Problem found. Had a nice big fibre washer hand, enlarge the hole a bit and reassemble. That works much better now, and it cranks over as it should. Whoever overhauled the starter made an assumption , that might be safe on modern starters, but wrong in this case.
jp