Author Topic: Hall trigger ignition on hit'n'miss exhaust pushrod?  (Read 155 times)

Offline rklopp

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Hall trigger ignition on hit'n'miss exhaust pushrod?
« on: November 24, 2021, 12:44:45 AM »
I am building a Breisch/Peters 1/2-scale Olds Type R hit-and-miss. I want to use a Hall effect sensor as an ignition trigger, with triggering from a magnet on the exhaust valve pushrod, but I am concerned about double-triggering. The plans call for old-school Kettering points that trigger from a ramped cam on the pushrod. With points, the ignition will fire when the points open, but will not fire when the points re-close. They re-close 360 crank degrees from firing, meaning at or just before TDC at the start of the intake stroke. If I use a Hall sensor, the ignition will re-fire at this point. Do I risk lighting off the fresh charge just as it's coming into the cylinder, perhaps causing a backfire? Has anyone successfully run a hit-and-miss with a Hall sensor triggered from the pushrod?

I have a Breisch 1/3-scale Associated Hired Man with a Hall sensor triggered by a magnet on the cam gear, so there's not risk of double-firing. I would like to avoid putting a magnet on the cam gear on the Olds, if only for "authenticity." (Yeah, I know, Hall sensors are not exactly authentic, but neither are over-scale points.)

« Last Edit: November 24, 2021, 05:57:24 AM by rklopp »

Offline Jasonb

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Re: Hall trigger ignition on hit'n'miss exhaust pushrod?
« Reply #1 on: November 24, 2021, 07:28:44 AM »
Mixture is unlikely to ignite until it is compressed so should not be a problem.

Depending on who's ignition you are using you could change to just a metal contact which just uses 2 of the three hall connections, that's how I mostly fire the S/S ignitions and often looks better than a hall sensor and it's wiring.