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Lucas Mag' Earth Brush Holder Thread

cinquecento

Well Known and Active Forum Website User
Non-VOC Member
.. can anyone tell me the thread size, in anticipation of having to reset timing at some point and not wanting to go through the rigmarole of adjust, set, amature slips; I'd like to make up a 'locking tool' to insert through earth brush holder.

Yes, I understand there is an technical article somewhere on the site re this tool but my 'pute just runs too slow and life's too short.

Ta' in advance.
 

Magnetoman

Well Known and Active Forum Website User
VOC Member
I'd like to make up a 'locking tool' to insert through earth brush holder.

Keep in mind that unless the hole for the earth brush was drilled and tapped precisely over the centerline of the armature, and precisely perpendicular to it, and unless the tip of your locking screw is precisely flat (and perpendicular, etc.) screwing it down will impart a rotation to the armature that defeats the purpose. This can be minimized by it either having a freely rotating "foot" on your locking tool (like on a 'C' clamp), which would be a lot of trouble to make, or by making it with a blunt tip instead of a flat on its end.
 

Kansas Bad Man

Well Known and Active Forum Website User
Non-VOC Member
I'd like to make up a 'locking tool' to insert through earth brush holder.

Keep in mind that unless the hole for the earth brush was drilled and tapped precisely over the centerline of the armature, and precisely perpendicular to it, and unless the tip of your locking screw is precisely flat (and perpendicular, etc.) screwing it down will impart a rotation to the armature that defeats the purpose. This can be minimized by it either having a freely rotating "foot" on your locking tool (like on a 'C' clamp), which would be a lot of trouble to make, or by making it with a blunt tip instead of a flat on its end.


The KISS approach would be , using a 6 point box end wrench that fits the point plate bolt. heat and bend a tab that fits the snuggly too the mag outer diameter, hose clamp tab to mag housing.
 

nkt267

Well Known and Active Forum Website User
VOC Member
All of the above replies apply..I ran a 5/16 BSF plug tap into the hole,making sure that I did not touch the armature.I chamfered the thread at the end and polished it to remove any machining marks that might mark the armature.
I had no trouble holding the armature still whilst the locking tool locked the armature..You could epoxy some friction material or hard rubber on the end of the tool to avoid any damage..the tool does not need to be wrenched up really hard to do it's job..John
 

Magnetoman

Well Known and Active Forum Website User
VOC Member
The KISS approach would be , using a 6 point box end wrench...
Simple is better only if it actually is simpler, and if it does the job. Because the "radius" of the bolt head is so small the normal tolerance of a spanner would allow rotation of at least a degree or two to begin with, and that's assuming attaching the hose clamp didn't move it. Maybe it's just me, but if I were to do this, an appropriate fastener for the earth hole seems at least as simple to make, easier to use, and almost certainly would have better final results.
 

Kansas Bad Man

Well Known and Active Forum Website User
Non-VOC Member
Simple is better only if it actually is simpler, and if it does the job. Because the "radius" of the bolt head is so small the normal tolerance of a spanner would allow rotation of at least a degree or two to begin with, and that's assuming attaching the hose clamp didn't move it. Maybe it's just me, but if I were to do this, an appropriate fastener for the earth hole seems at least as simple to make, easier to use, and almost certainly would have better final results.


A degree or two would only matter if the timing was perfect for a given day and a given fuel, remember
you are only talking 1/2 to 1 degree as the mag is half speed of the crank. The timing of the Vincent varies from machine to machine. I have had to many Vincent's on the dyno to InterTAN 1 degree.
 

Magnetoman

Well Known and Active Forum Website User
VOC Member
A degree or two would only matter if the timing was perfect for a given day and a given fuel, remember... The timing of the Vincent varies from machine to machine.
Yes, I completely agree with this. But, if someone is trying to dial in their particular machine they need to be able to reproducibly set the timing. If they are having trouble doing this without the magneto moving, and they want to use a locking tool of some kind, they need that locking tool to be as reproducible as their ability to determine BTDC. Otherwise, there's no point to it.
 
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