Lucas magnetos

[tractorman]

Hi, can I use an armature from a clockwise rotation magneto, in an anti clock mag, just by changing the slip ring from left hand to a right hand one ?

[Rex]

Yep.

[rogerwilko]

The points have to be changed too if its a ring cam type. They are handed, i have both types.

[cardan]

Why do you need to change the slipring? Surely the maximum flux point is the same regardless of direction of rotation, so the HT brush will be in contact with the slipring at the time of the spark regardless of which way the armature is spinning. As rogerwilko points out, the points arm needs to match the direction of rotation (rubbing pad always trailing), and be sure to check that the key that locates the points block has the points opening at the maximum flux point on full advance. Presumably face-cam magnetos don't mind too much which direction they rotate, although I suppose they're a little different because the magneto is timed to have the points opening at the max flux point when the magneto is at full advanced. It pays to check any "swapmeet" magneto!

Leon

[esometisse]

the points should open just after the magnetic field changes its direction. This certainely doesn't happen at maximum flux point, so the position of the pickup brush on the slip ring is different for the different directions of rotation. Thus for a twin the slip ring has to be changed if the direction of rotation is changed even if the firing interval is even - i.e. parallel twin.
For a single, however, it doesn't matter as the slip ring's circumferential surface is not interrupted by non-conducting portions.

Cheers
Andy

[tractorman]

thanks everybody, I thought it was just a slip ring change, but best to ask the experts first. I take the point about contact breaker and cam ring but this dosen't apply as I am robbing the armature only from a working clockwise mag to put in a non working anticlock mag

[rogerwilko]

I,m too lazy to check but doesn't the ring type just flip around? The face cam ones do.

[cardan]

Senior moment in my comment above - I wasn't thinking about a twin. I'm not sure about Andy's comment, since all Lucas magnetos I know of have fixed magnets, so the field is static; it never changes direction (although it gets complicated by the iron in the rotating armature). I'd say "theoretically" the best time to open the points is when the induced voltage is highest in the primary circuit; this happens when the rate of change of magnetic flux is highest - simplistically when the primary coil is at 45 degrees to the field. But of course the shaping of the pole pieces and the iron in the armature create a rather complicated field arrangement as the armature rotates.
So all my comment above are pretty-much theoretical waffle: just make sure there is significant resistance to rotation at the times when the points open (never perfect for a V twin, or course), and that there is one (and only one!) HT brush in contact with the slip ring segment when the points open. Flipping the ring might do this, but you'll need to check.
Leon