Magneto direction

[willowbedone]

can anyone answer a question from a good friend of mine Can a magneto which the arrow on the casing shows clockwise rotation be used with it turning anti clockwise
Thanks Ian

[aobp11]

Ian,

That will work when the field coil wires are interchanged or the brush connections are interchanged, and the dynamo "flashed" to be sure it's polarised for the new application.
But... when it's that simple, why have an arrow on the casing as if there were really different models? I guess that's because of the so-called armature reaction. Given the way the windings are connected to the commutator segments, that effect is not the same for both directions of rotation. The winding/segment/brush structure is more or less optimal for the arrow direction of rotation, and bad for the opposite direction. More on this for instance here: https://en.wikipedia.org/wiki/Armature_ ... gineering) .

Albert

[dave16mct]

Are you getting mixed up Albert? The question is about a magneto.
Cheers Dave.

[Harry44]

I'm no expert on magnetos but:

When turned the wrong way the points will open where they should be closing. This will be a long way away from the peak voltage provided by the generating coils. So if you do get a spark it will be very weak.

[aobp11]

Ah yes Dave! I immediately associated an arrow on the casing with a dynamo.
Thanks,
Albert

[Groily]

The answer is yes, but some small parts will need changing or modifying and it can be a fiddle.

A twin cylinder mag will need a differently-handed Slipring on the inside; its camring will need repositioning; and it will need the opposite-handed contact breaker assembly if it has a brass backplate. The heel on the opening cb point with the long spring blade attached needs to TRAIL. But no need if it has the later low inertia steel assembly which is symmetrical and can work both ways provided there are 2 contact points on the fixed part (which will now be working in the opposite sense with the opening point reversed on its pillar: some points sets only have a rivet where the original Lucas item would have had a 2nd contact point to facilitate this very thing.)

A single can be done more easily as the slipring will not need changing so you don't have to play with the armature. (There are some BTHs where the slipring will need changing however, as they didn't use rings with 360° of brass on them in all single cylinder applications.)
If there is a face-cam cb assembly (eg N1 as standard, MO1 magdynamo) then all that is needed is to reposition the Camplate by cutting new notches, so that the points open at the right moment when turning the other way. The right moment is 'a very few degrees after the flip point' with the camplate fully advanced.
A single with a camring (MSL for example, or N1C or R) will need the camring repositioning and the cb assembly changing as above if it is handed.
In both cases, tight and slack will be reversed henceforth in terms of cable position for advance and retard.

With a single, it is also desirable to maintain a negative spark (which jumps from centre to earth electrode). That may be possible depending on exactly how things are set up. But if using the second magnetic flip point, which is often the case, then the polarity will change absent reversal of the magnetism.

It's not THAT hard to do, but it can be a bit delicate to get the internal timing right, and it's a pain extracting bearing races if the slipring has to be changed.

[willowbedone]

Thanks everyone this has helped We can now sort the mag it's a moil magdyno which will just need the slipring changed over
Thanks
Ian

[Groily]

Noooo! The slipring certainly won't need changing (see previous comment).
It will be OK (unless it has other faults) as the direction of rotation doesn't come into the equation with MO1s. The slipring has brass round it through all 360° of itself, and will work both ways.

What you do have to do is sort out the camplate and the internal timing so the points open at the right moment relative to the magnetic flip point after the reversal of direction. Not the same thing at all. Lucas made camplates with an R and plates with an L stamped on them - but it's not (usually) hard to convert from one to the other as I mentioned earlier by making suitable notches for the AR cable and for the plate's movement.

There is absolutely no need to take out or play with the armature at all unless there is some other problem. (There might well be if it's original, tis true . . . but it won't be relevant to this issue.)

Almost the only Clockwise drive MO1s on Brit iron are for Norton singles (pre-1934 I think, the year when they changed the timing gear arrangement with the effect that the mag then went anti-clock like nearly everyone else's). And just maybe - haven't checked - some REs. Some of their twins went clockwise, but not sure on COs or Bullets).

[willowbedone]

Sorry groily I meant to say the cam plate not the slip ring I will have a go at modifying it
Thanks
Ian

[willowbedone]

So am I right in thinking anticlockwise viewed from points end should have a camplate marked with an R and clockwise viewed from the points end should have a cam plate marked with an L ?