The drive from the crankshaft is by spring belt so a small pulley with a vee groove is required. Turn down a length of mild steel bar to 15mm (0.590") diameter and turn down additionally a spigot of 6mm (1/4") diameter. Drill through 2.5mm (3/(32)") to finish a tight fit on the governor shaft. Drill under size and then finish with the right size drill which usually gives a good fit, though you might like to try on a piece of scrap material to check the fit. Put in the vee groove using a 60-degree thread turning tool and part off. Though I have not tried it yet I was chatting to a friend at an exhibition and he came up with a good idea for using spring bands on small diameter pulleys, which can be prone to causing the belt to slip. The idea was that instead of turning a vee groove to turn a square sided groove and to fit into the groove two tight fitting O-rings. The side-by-side O-rings form a natural vee groove into which the spring band can fit and the rubber of the O-rings provides a good grip for the spring band.
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