Hi, thank you for your replies.
I’ve got a little further towards a cheap solution to emulate a gold star style tachometer for my plunger.
Initially I thought I would need a 2:1 reversing gearbox in the cable after my Austin Healey 1:1 angle drive to power a 4:1 clockwise tachometer I’d seen on e-bay.
I looked for g/boxes but all were as expensive as the 4:1 reversing angle drive original to the gold star.
Then I thought of making my own box from meccano gears but perhaps a bit too ambitious for a neat solution.
An e-mail prompt from e-bay showed me first a 4:1 clockwise tachometer, then a 2:1 clockwise, then a 4:1 anti-clockwise, and then eureka, a 2:1 widdershins (anti-clockwise) tachometer for an incredible cheap £16, probable cheaper than the cable I’ll need to drive it.
So I hope I’ve got this right. The magneto turns anti-clockwise at half engine speed, my Healey angle drive turns this 90Deg non-reversing with a straight cable into the back of a 2:1 anti-clockwise tachometer.
Muskrat warned me about drag on the auto-ignition advance mechanism, so thank you. I had to look at my auto-advance to see why.
I understand it now but don’t want the expense of changing to a manual magneto especially as I plan to only adapt the points system on mine
to switch a SparkRight electronic unit, another cheap modification using parts I have laying around. You may see a trend here when it comes to spending money, but many kids and even more grandchildren, car projects, house maintenance and shiny bits for the plunger all take a toll on my little pension.
So I looked again at my auto-advance system and think I could mount a square pin needed to drive my angle-drive onto the four stops that limit the movement of the bob-weights under centrifugal force at high speed negating any drag from the cable on the armature.
I’ll have to accommodate access for a spanner to the nut and allow easy coupling to the collar I’ll turn up of my lathe that will be mounted on the timing case cover to hold the angle drive.
So I need to stop talking about it and actually do something.
Thanks again,
Steve.