I have been rebuilding the Lucas
MO1L magdyno from my 1955 Royal Enfield 350 G2 Bullet over the last few weeks and I think I now have a pretty good understanding of how everything works.
There are still some grey areas and I was hoping someone could maybe help to clarify things for me regarding the magneto points cam and it's advance/retard mechanism?
The magneto section from my bike is anti-clockwise rotation with a right hand spring (which I believe refers to the advance/retard cable entry) and a left hand HT pick up. This is as viewed from the drive end (timing side of the bike).
If you refer to the first of the attached images you can see the cam in position in the housing in (what I believe to be) the fully retarded position. Looking at the cam from this end view the rotation of the contact breaker carrier is clockwise and you can see that there is a rectangular notch at the bottom of the cam that allows the cam to rotate by approximately 32 degrees. The edges of the notch stop it rotating any further in either direction by hitting the stop screw in the magneto drive end housing. You can see the ramps that the contact breaker tappet ride over at about 7 o'clock and 11 o'clock. This means the points open at about 11 o'clock, as the the tappet is pushed up onto the raised section of the cam. The points stay open for about 270 degrees until the tappet goes down the second ramp at about 7 o'clock and then they stay closed for about 90 degrees. Rotating the cam with the advance/retard mechanism in an anti-clockwise direction will advance the ignition, as the ramp which opens the points will, in effect, be getting hit earlier in the cycle? I believe I am correct in this thinking and if I am then the ignition will be fully advanced when the advance/retard cable spring is fully compressed? Turning the handlebar control lever to un-compress the spring will make the spring push the advance/retard plunger down and turn the cam anti-clockwise to the fully advanced position?
This fully advanced position is as seen in the second image.
So, my first question is am I right in how I believe the advance/retard mechanism works? How would you normally go about using it in normal operation?
When I used to ride the bike regularly, as a youngster, I cant even remember having an advance/retard lever on the handlebars?
Secondly the notch that the advance/retard mechanism engages with is not alone. There are three of them. I am guessing the one at about 4 o'clock will be for housing with the advance/retard cable entry at the other side? But what is the third notch for, which is in about the same position as the top cam plate ramp?
Thirdly, what is the mark stamped close to this mystery notch? Is it the letter 'L' or is it an arrow?
All of these things I would like to know in an effort to make things clearer in my head. I'm never truly happy until I know that I have got things right and my understanding is clear of grey areas. My wife says I am autistic, my friends call it anal. lol