Dimensions and shape of toothed ring

[robert verhey]

Are there any specific limitations to the size and the shape of the 36 - 1 toothed wheel?

The standard toothed ring has main dimensions
OD 144 mm ( 5.7 inch )
ID 128 mm ( 5 inch )

For various reasons i like to install a toothed ring with the following dimensions:
OD 100 mm ( 3.9 inch )
ID 91 mm ( 3.6 inch)

For ease of manufacturing, the shape between two teeth I like to have as half a circle. Will that work?

FYI, the ignition will be for a Willys M38A1, 1955, F head engine.

Thanks,
Robert Verhey
Finspång, Sweden

[MartinM]

Hi Robert

Have a look at the trigger wheel styles on www.trigger-wheels.com - they can be quite varied!

I'm pretty sure that you should have equal tooth:space ratios

You'll also see on the examples on that page that the shapes are not half circles...

[steve100]

Robert
I have made a ring from a 7 inch dia aluminium disc with 36 holes drilled in it with 35 x 832 (approx 3mm dia)steel bolts & nuts. The spacing is about 2-3 times the bolt diameter and it works just fine. All you need is a regular approx sine shape wave and the missing pulse. The flux generated by the ferrous bolt does a fine job. I wouldnt worry too much about the shape - particularly the base shape.
regards
Steve