I have been through several designs for the ignition cam. I made the first one from brass as indicated in the plans, but decided not to use it because I was going with the hall sensor.
The second one was made from plastic (Delrin, I think), and was on the engine for quite a while. You can see where the magnet is mounted. I glued it in with super glue. I also removed the screws attaching it to the flywheel and added a setscrew so the timing could be adjusted without moving the flywheel around.
The final design is a governor mechanism that I designed to keep the rpm's from getting too high ( detailed in another post).
You can also see the Delrin stand that I made for the Hall sensor.
I'm glad to see others building this engine. I haven't seen another at any of the shows I attend.
This one was a bit difficult to get to run properly, but I eventually fixed it.
The biggest issue was compression - make sure your piston is an extremely close fit to the cylinder.
Happy building and Happy Holidays!
Scott