Thanks John.
That Vincent set-up is incredible. Trouble I'm facing, as with most aftermarket manufacturers, is having to work around issues that could easily have been avoided had an electric starter been envisaged from the outset. Remember originally this engine was destined for race use, not road. Hence the large belt drive, capable of transmitting 100+bhp. Another reason for choosing that was the ability to make the engine sprocket much larger, in order to reduce torque on the gearbox. Clearly with a vee twin in a frame designed for a parallel twin, things are tight in places, limiting my choice of starter placement. For example, I have space above the gearbox a la Vincent, but alas the intake manifold for my rear cylinder precludes putting anything there. No room at the front either, unless I change the forks to a bobber style! No room between engine and frame, then there's the front exhaust pipe between the downtubes ......
Before this exercise I'd not paid much attention to sprag clutches, though I was familiar with them from auto gearbox repair. What I find is having a sprag and bearing combined in one unit severely limits torque and speed ratings. For example, a CSK40 will transmit 385Nm of torque (I need more like 500) but has a max overrun speed of 3,000rpm. A CSK15 will stand nearly 3x those revs, but only transmits 20Nm. A sprag alone (fitted to suitable shaft and housing) and oil lubricated are often rated 3x those figures and with unlimited speed. Altogether a real pain.
As for alternative ratchets, I had toyed with a face ratchet (larger version of our kickstart ratchets). That would, as Neil discussed some while back, address the issue of having too many degrees between consecutive pawl engagements. Trouble is I can't see any way to engage that other than manually. There just isn't the crankshaft room for fancy face cams to initiate engagement.
