While waiting for the Busa motor to turn up have been working with Greg Watters on how to get another gear happening.
Greg's build diary is here:
http://www.dlra.org.au/forum/viewtopic.php?f=18&t=2006 A proven runner on a sit on bike.
We look at a fair few options from making one out of a car gearbox, Lenco 2 speeds, drag bike 2 speeds etc. most of the were too hard, to big or to expensive or any of your imaginable combinations of those options.
Ideally what we were looking for would fit in the standard chain line width, be small diameter, strong and cheap.
In among our research we came across the Laycock overdrives that at first look had nothing going for them other than small and cheap.
Wasn't after an overdrive, we wanted underdrive and the sprag clutch locked up in the direction that we it would turn in a bike.
We looked at trying to turn the sprag clutch around but as always the real solution is simple.
Turning the box around so Input becomes output and vide versa we now have an underdrive box that turns the way we want.
It can't be that easy though as the box will now want to start off in direct and not have enough pressure to shift to low until moving at speed, that doesn't really help us much.
By having a look at the hydraulic circuit we have worked out where to plug a few galleries and drill one so that the internal pump only runs as a lubrication circuit at 20 psi rather than the 450psi it normally works at.
The shift will be done by CO2 with pressure to hold it in underdrive then releasing to go into direct.
Woodshed and Underhouse engineering at its best, strong, small and home built.
27% is a big gear step but shift it first then it's got I put and output shafts locked together and just along go the ride.
One downside is that the bikes CANNOT go backwards in underdrive, I stripped on today and remove a couple of the springs that hold it in direct and packed the pistons so that it is in underdrive, it works the way we want but will not rotate the wrong way.
Cheers
jon