Author Topic: k2f magneto location of fiber washers on points. Solved!  (Read 234 times)

Offline oldbikerbill

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  • 1954 Bsa A10 Plunger. Located outside San Diego,
I'm just getting my '53 A10 back on the road after 3+years sitting in my barn.  I cleaned out the carbs, adjusted the valves and checked the gap on the points, which were too close.  So I took them out  and ran a nail file between them to clean off a little pitting and now that I'm putting them back in I have an extra fiber washer and there is connectivity between both the plate and the point bearing arm.  I have a fiber washer under the set screw, and under the center bolt.  Any exploded diagrams that show their location or pictures or a simple explanation would be very helpful.  Thanks in advance.
Bsa A10 Plunger, '72 Moto Guzzi Eldorado,'73 Bmw r75/5

Offline groily

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Re: k2f magneto location of fiber washers on points.
« Reply #1 on: 05.04. 2019 07:38 »
There are some pics here which might help a bit: http://www.brightsparkmagnetos.com/easycap/index.htm
Ignore the green circuit board - that replaces a simple insulator that normally goes between the brass block that holds the fixed point and backplate in a standard installation.
There are insulators going through the smaller off-centre hole of the brass block that takes the fixed point; a similar but bigger thing passes through the backplate, with a little tophat on the outboard side, to stop the centre screw touching the backplate as it goes through the assembly, and there should be a fibre or other insulating washer under the head of the smaller screw, to ensure that the brass block is insulated from the backplate proper.
No insulating washer under the head of the centre screw.
Little dimpled plastic or fibre tit sits on the opening point, to locate it under the springy arm that helps keep it on its pivot post - it but doesn't 'do anything' in an electrical sense.

The opening point should be permanently connected to the backplate (earthed), via the small screw at the end of the spring blades.
The fixed point and its mounting block should be insulated from the backplate but in contact with the centre screw.

With the cb assembly off the magneto, or with the centre screw withdrawn if on the bike, you'll see no continuity across the points when they are open.
With the centre screw in place, you'll see the resistance of the primary winding, about half an ohm, across the points when they are open, or zero if you're lucky with them closed.
The centre scew is attached at its bottom to one end of the primary, the other end of the primary is permanently earthed in the armature. The arrangement ensures that the centre screw and fixed point (which are 'live') are insulated from the backplate, while the moving point and the cb backplate are earthed always.
If those things check out OK, then there shouldn't be anything to worry about.

In the event you have the later steel cb assembly with more car-like points, the arrangement is different. The opening point is live, the fixed one, on the 'butterfly-like' bit, is earthed. There must be a fibre insulator under the head of the small off-centre screw that attaches the fixed point, which sits on a figure-of-eight-like insulator that locates on the backplate. The electrical arrangement is reversed, but the principles of what is in contact with what and when are the same. Fitting and removing the centre screw has the same effect on continuity. Failure to fit the insulating washer under the head of said screw will create a link straight from live to earth and kill the system dead. The reason these assemblies are fiddly to mess with is that they are designed to operate for either direction of mag rotation (assuming there are 2 fixed contacts provided), whereas the earlier brass sort are handed according to the required direction.
Also very important, as has been said here many times by many people, not to allow the spring blade on the moving point to kiss the camring as things go round - as that creates a short circuit on the primary.

Hope this helps a bit.
Bill

Offline oldbikerbill

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Re: k2f magneto location of fiber washers on points.
« Reply #2 on: 05.04. 2019 16:41 »
Thank you.  One last question, I appear to have the late type, as you describe, so there should be a fiber washer on the center screw.  Should there be a washer at the bottom of the post that the moving point rotates on?
Bsa A10 Plunger, '72 Moto Guzzi Eldorado,'73 Bmw r75/5

Offline groily

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Re: k2f magneto location of fiber washers on points.
« Reply #3 on: 05.04. 2019 17:09 »
There is a thin insulating washer usually (sometimes more than one in fact) under the heel of the opening point on the pivot post  to ensure a) it's isolated from the backplate and b) to assist with alignment of the mating faces of the points.
Should be one on the top of the pivot post too, under the star washer that holds things together.
There would normally be a steel lockwasher under the centre screw's head - the underside is flat on those screws, not tapered - but no insulator.
Cheers.
Bill

Offline oldbikerbill

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Re: k2f magneto location of fiber washers on points.
« Reply #4 on: 06.04. 2019 03:36 »
That di it!  Got a nice fat spark!
Bsa A10 Plunger, '72 Moto Guzzi Eldorado,'73 Bmw r75/5

Offline groily

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Good News and well done. Hope they stay fat and happy  . . .
Bill