Magneto points open at 5 o'clock ??

[john.nash]

I am just about to time my WNG (still being assembled and waiting for some bits; but I am this far) with it's M01L

I got a secondhand magneto which sparks strongly (thanks Pete Collings - who put a new points block on it etc.).
However, I would usually be expecting the points to opening around the 10/11 o'clock position.
On this they are wide open at that point and they are closed/opening around the 4/5 o'clock position ???

It's marked anti-clockwise (correct) and it's a tightwire type -cable take off on the right as you look at it, which is also correct.
Sparks when spun both ways...

I don't see why I cannot time it at the 4/5 o'clock position ..?

[Steven.Carter]

I suspect the bump is around 11:00 to make it easy to get the fag paper in so like you said it shouldn't matter where the ramp is but could there be something loose?

Steve

[john.nash]

The points block only goes on one way ?

Looks like the points should be fully open, on this one, is at 4/5 o'clock ?

Seems odd? Wrong cam?
Does it make a difference ? I have a mag timing light, so the fag paper ain't that much of an issue ?

How can I tell a clockwise from an anticlockwise?

[Steven.Carter]

Theres another cutout on the cam plate above the one your using, stick it in that one? perhaps.

[pete.collings]

I have never discovered if there is any significant difference between the basic operation of a clockwise and anticlockwise rotation MO1 magneto, although there is for the twin K2F magneto, which has a different slipring.
In essence, the points should close and then open around the period of maximum magnetic flux, felt as a pull or resistance when rotating the armature, this is when the armature primary windings will be generating the most electrical power, the abrupt cut off of which (by the points opening) generates the high voltage in the secondary windings and hence the spark.
The shape of the cam should reflect this, I have come across cams with the flat in the wrong position to give a spark, these may have come from one of the other types of magneto made by Lucas.
The cam plate bottom has a slot to allow rotation of the cam to advance and retard the timing, the peg that locates this is eccentric, I believe that on manufacture this was rotated to give the best spark at full advance. The points gap is also important, too large a gap will advance the timing and lessen the time the points are closed and generating primary current, too small a gap will retard timing and possibly lead to more sparking across the points, no gap (when the points tappet wears through no lubrication) means no spark!
So long as the cam fulfills these requirements, evidenced by a good spark, having the points open 180 degrees from the usual Ariel position should not affect its operation, although it might be easier to drop the fag paper if using this method of setting the timing!!

In answer to Steve's suggestion, the position of the camplate is fixed by the bottom peg, so the top one cannot be used, it may be that this camplate was designed for use in more than one type of magneto.

[john.nash]

Tee Hee
Been sat here fiddling with it.

It is a cam-plate thing.
Had a scrap magneto with a different cam-plate.
Mine was marked "R"; t'other one as marked "L" and it now does what I think it should (I think) AND it still sparks !

I reckon it would spark, as you mention Pete, every 180 degrees but the cam plate decides when.

I have learned a little more tonight ....

[nevhunter]

An ordinary single magneto can correctly spark at 180 degrees. The points have to open in relation to the stage at which the magnetic flux in the armature changes direction. This is when the electrical energy is induced into the primary coil. You should check where the spark is strongest in the direction of rotation that you are using. It should be when you have full advance. If your magneto sparks in both directions it may try to run backwards when it kicks back. While it won't do this for long it may injure you. Another camplate will remedy this and it will have a different opening period to prevent that.
I had a Scott that would go from idling forward to running quite well backwards, without stopping which understandably freaked my wife out when she was riding it as it usually happened in traffic when you couldn't detect the change in engine note. The engine had to be idling slow for it to happen. Nev

[john.whiting]

Ive reversed magneto and generator direction for both my Nortons,as anything Norton is dearer. Norton reversed direction in 1935 and changed back in 1948.In a MO1 the only difference is the camplate,with the advance as you prefer it.Grind another notch in the plate in the correct spot,and rotation is reversed.The long generator only requires the leads swapped,but the short generator needs a longer lead fitted .Regards John.