1978 R80 ignition advance

[nickrides]

Hi Gents
I recently tuned up my R80 and for the life of me I cannot understand how the ignition advance works.
I see as the RPM increases the springs move out and the timing advances, but how does the timing advance?
The cam lobe that lift the points seems fixed, How does this work? The point plate is fixed..
Thanks in advance

 

[20774]

Nick -

On the stock advance unit, there are two weights which are hinged to the central collar. The points rubbing block rides on this collar and the collar isn't perfectly circular but has two high points. As the camshaft spins faster, the weights begin to move outward in an arc...springs keep the weights from immediately moving to their outward limit...this controls the ignition timing advance. As the weights move out, and being hinged to the central collar, the collar begins to rotate. This rotation changes where the high points come into contact with the points rubbing block. The rubbing block is fixed and with the collar rotating underneath it, the point at which the high point encounters the rubbing block changes, and thus the point at which the points open to begin the spark plug firing sequence.

 

[nickrides]

Kurt
Thanks for that explanation, next time I'm in there I'll have to take another look.