Forum

[Beezabryan]

Just wondering why?

[stinkwheel]

Why?

A distributor on a single cylinder engine is a bit of an oddity and a relic from the days when these bikes had magnetos. The sensible and logical place to mount the ignition timing mechanism is on the end of the crank.



There are 4 gears between the crank and the points cam, one cam sprocket, two idler gears and the dizzy drive gear. There is play on all of them. It adds up to a LOT of backlash. Anyone who's tried to set static timing on a 350 bullet the the cam in the retarded position will realise just how much.



With the timing on the end of the crank, this is completely eliminated. I'm planning on building quite a poky engine and + or - 5 degrees of slop on the ignition timing is a lot in anyones book. I'm building this bike from scratch so I'm looking into ways of making it as good as it can be.



It would then be tempting to put something fun on the end of the dizzy shaft. Like one of those optical illusion spinning discs. Or a mechanical siren. Or more sensibly. Remove the idler gears altogether and blank off where the dizzy casting attaches.



Bullet whisperer posted a video recently showing just how much backlash there is. https://youtu.be/4aQc2cv5kmY?t=2m48s

[binary]

There is zero backlash in my motorcycle ignition. There are no idler gears and no distributor. There is an after market ignition control module (black box) that has a screw on the side to adjust the timing. I bought one of these but I have never tried it as my ignition with the Indian ignition control module that came with it works perfectly. Crank shaft timing is much better than the Boyer Bransden inside the distributor kit. If you can find a crank mounted ignition that will work on the existing drive shaft of your motor you will certainly save a lot of time.

[binary]

Hopefully here is a picture on the drive shaft showing the position of the reluctor and the need for the longer drive shaft.