This shifter cam is what makes it happen. The FX (34006-74). Above and below are complete views of the gate path.
There was a slight discourse with my co-author about whether my jockey shift-pattern opinion was subjective and out of line with the rest of the Vol.2 contents. I agreed that I went "over -the-top" and needed to be reeled-in, and removed a single paragraph in Chapter C., but kept the trans. photos in there because they relate to jockey and ratchet assemblies.
My own interest in Knuckle and Pan OHV is focused solely with surfing on asphalt. The information below will be of no interest to most people, but it has a history.
I heard about the FX cam from Lakeside Bill.
He furnished the FX shifter cams. My co-author knew nothing about the FX cam (shift pattern reversal), though a (younger) line-mechanic at San Diego Harley-Davidson, overheard the open discussion we were having, in 1997, near Randy's service-bay, and voiced his agreement (with me) that there were two shifter cams produced between 1971-1979, ; but nobody listened to him so he shrugged his shoulders, and went back to installing throttle spirals on new floor models that were being service-readied. Years later, Stett did explain the reason why the FX shifter cam came to be; (FX had a shifter shaft that went through the middle of the primary and H-D need to create another shifter cam that would allow the shift arm, swing movement in a tight space).
You can install this shifter cam as a straight swap-out with the earlier cams and drums in a ratchet top, and create a jockey shift set-up by removing the mousetrap and installing a new front brake cable, cutting off the the brake cable tube to 12", and moving the brake lever to the left handlebar. Nothing but the brake cable tube is permanently altered.
This is all about un-weighting on water and on land. When you un-weight, you float for about a milli-second.
Focus on the inside face of the wave. That's where you want to be on a surfboard - inches away from the face of the wave - In the sweet-spot of a horizontal tornado - under the lip. Taken from the front, the wave looks flatter than is actually is. You could easily fit two Big Twin's riding side-by-side under that lip and neither of the handlebars would touch the water on either side.
The sweet spot is within the hook. There's safety in the hook. Touch either one of those sidewalls though, and your going to get sucked up into the face of the wave or slammed towards the sand-bottom by the lip.
The hook is like being in third gear in the middle of a banked curve on clean asphalt. Torque is wound up. Speed is 25-35 mph.
A few more photos will try and parallel the effect obtained between 2nd and 3rd gear, and bring the entire concept full circle (or as with an OHV motor, 720 degrees - two full circles).
It all has to do with piston diameter, stroke, heavy flywheels, firing degree and duration, and a foot pedal. Those mechanical elements produce the same ground swell as this wave, that moves onshore with the inertia of a turning flywheel.
So, here's the wave (reversed image). If you look ahead of R. McBride (whose inches away from the inside wall), towards some spot that's gathering to develop a hook, where you'd think you were going to find the apex of all gathering-energy to dig into a turn and change direction, well then,
that is same spot in a banked road turn, where you (back-shift) from 2nd to 3rd gear or 3rd to 4th, and release the foot lever.
Big Twins surge more with jockey lever/foot clutch release than with footshift/handlebar clutch lever release - (and a tank shift is 180 degrees, a different ride than stick).
You can see the rigid section of a swing-arm frame dip rearward on a footshift Duo-Glide, if your standing from behind, watching it pull away from a dead stop. That's the same punch that gets transmitted to your rear tire, when you release the foot lever and twist the throttle coming out of a curve, riding with a rachet top and FX shifter cam.
There is no ride like it. Not on land, there isn't.