The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Lucas, Ignition, Charging, Electrical => Topic started by: PatM20 on 03.04. 2018 08:25
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Should there be electrical continuity between the points retaining spring clip and the shoulder of the points or is there some sort of rubber grommet the size of a small ball bearing that fits in the hole on the shoulder of the points that the spring clip locks onto?
Regards
Pat
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Lots of different sorts of points but this link to an image from Brightspark may help if it's a standard brass set.
brightspark magnetos (http://www.brightsparkmagnetos.com/images/Exploded%20CB.JPG) note then fibre washer (ignore their green easycap condenser)
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........... or is there some sort of rubber grommet the size of a small ball bearing that fits in the hole on the shoulder of the points that the spring clip locks onto?
My understanding of this is 'YES'...kinda resembles a very small sombrero
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On the brass points assembly, the fixed point is 'live' and attached to the low tension armature winding by the centre screw.
The opening point is 'earth'.
So whether the retaining clip is insulated or not makes no electrical difference because the post, the clip and the opening point assembly are already to earth.
But something is needed to help keep things in position. The original little bobble, often reddish, was smaller than the black plasticky sort supplied with replica points.
It is worth underlining the fact that with the later 'low inertia' steel backplate and more car-like points, the opening point is live, and the fixed one is earth. So in that case it is vital that no part of the opening point - notably the spring blade - touches an earth. No bobble there, but absolutely crucial to have the right insulators in the right places.
If running around the cb assembly with a meter, what you want to see is 0 ohms across the points when they're shut, and - with the cb centre screw off - open line when they're open. With the centre screw in place, you'll see half an ohm when they're open, which is the resistance of the primary winding, and when they're shut you'll probably see a rapidly rising resistance as the meter (tries to) charge up the condenser.
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Thanks for this.
I made up a small grommet from a rubber tap washer.
Regards
Pat
ps tap washers are brilliant for all sorts of stuff as is CT1 and black mouse mats!