Speedo threads

[Alan]

Does anyone know the thread size on input to a PA type governor speedo? Thanks.

[Austin in the Shed]

3/4”x26.

[Alan]

Thanks Dave

[JonE]

Are you also trying to find a die after a mazac failure repair, Alan?!

[Alan]

No, I’m thinking about a reduction gearbox to correct speedo inaccuracy

[Dave Mann]

You could fit a bicycle speedo which is probably easier and cheaper to fit, I fitted them to our cars and found that two PA speedos read correctly and one 3 mph fast.

[Alan]

I’ve got a bike speedo on the RL but I want the original speedo on the chummy to read correctly. It’s a belt drive that provides 3360 turns per mile into a 2240 instrument.

[Dave Mann]

If the chummy has it's original speedo why is the belt drive incompatible?

[Alan]

I used original in the sense that I wanted the speedo that’s fitted to read correctly not to replace it with a bike speedo. The problem is it’s a belt driven system- that outputs 3360 turns per mile. The rather nice speedo head I have takes 2240tpm so it over reads somewhat. Options as I see it are new pulleys, a corrector box or just get better at mental arithmetic.

[Ivor Hawkins]

My speedo works but it it so inaccurate I ignore it anyway. Top speed so far downhill with the win£ behind me is 57 mph.