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At the humpy club meetings we have a "show and tell". Last night's did not disappoint.
One of the guys brought in what looked like a steampunk distributor rotor. And so it was . . .
He said it was from an air-compressor-on-a-trailer, powered by a grey motor, which the Defence Department was putting up for auction. The engine had a grand total of 12 hours time.
It's a distributor rotor to fit Bosch distributors, but almost circular and nearly fills the inside of the cap, and it had all this extra weird stuff hanging off it.

The normal brass "tongue" that rotors have was still there, but almost completely encased in Bakelite. Then about 150 degrees away was a brass block on a rod which moved in and out, retained by a coil spring over the rod. When the rod was at its full extent, it contacted a vertical pin mounted on a metal horse-shoe-shaped bracket riveted onto the Bakelite. The bracket was connected electrically to the detent spring which holds the rotor in position on the distributor cam (and earths it).

It's an overspeed cutout. As engine speed increases, the spring-loaded brass block moves outwards under centrifugal force, until the gap between it and the vertical pin is small enough for the spark to jump the gap, depriving the spark plugs of lightning. Engine slows down, brass block retreats inwards, and the spark plugs get their zap back.

That's not all. In the rotor there was also what looked like a resistor, probably for interference suppression.

Has anybody ever come across one of these distributor rotors?

And I'm thinking of a hypothetical situation in which a father is teaching his rev-head son to drive the family's grey-engined Holden, so he can go for the test on a manual car. This would perhaps be the ideal device . . .

Rob

Do you have a pic of it Rob?

Craig,

Unfortunately, no. I don't have a smartphone, but others who were at the meeting do. Should have thought of that.

Rob

ok no worries. From what you've written you're on the money. I saw a fair bit of this stuff when I was in. Rotors in magneto's and some other dissy's used these arrangements as rev limiters. One notable was the Rolls Royce Meteor engine in the Centurion tanks. Same thing utilising a spring loaded brass button. Also of note was all the double shielded wiring on everything not just the ignition to stop interference with the radio sets used for communications. Some say it was also for the reverse to stop outside interference effecting the engine but I'd only imagine something like a nuke blast doing that. Interestingly one tank they blew up in the atomic trials in SA was found to have run out of fuel and did not stop running becuase of the blast......I digress.

Off the subject I'm not far off testing all my balancers.....been busy as with Nationals prep. Time is fleeting.

Craig,

Yes. It's astounding. Madness takes its toll.

I'm with you on the radiated, rather than received interference.
And while on balancers - I got a batch of 70 duro rubbers made. A bit of an oops previously - I wanted 70 but ended up with 90. Well spotted.

Rob

The speed limiter sounds very, very similar to the ones used in Vertex maggies. There is some info on the design and adjustment in my grey motor magneto thread. Never seen one on a dizzy though.

The photo below is the one I have at home:
Cheers,
Harv

Humpy club AGM last night, so I was able to get a photo of the steampunk distributor rotor:
Big file. Should have compressed it before posting.

Rob

Now that is cool. Is it adjustable?

Cheers,
Harv

Harv,

Yes, it would be. See the tang that curves up above the brass plate? That'd be the anchor for the return spring. So you'd undo the two screws and bend the tang, thus varying the spring tension. Probably a factory setting though - you'd just order a maximum rpm and they'd come suitably set.

Rob