So, what happens next? We re-design every single part of the Hayabusa-to-Miata adaptor, that's what.
Re-installing the sprung hub is no simple task. Instead of taking torque off the middle of the primary drive gear, we need to take it from the other side of the sprung hub. We also have to allow for some rotation between the flywheel shaft and the primary drive gear, two parts that we brazed together into one piece. Look closely at this stock sprung hub and shaft and you can see the end of a needle bearing here between the primary drive gear and the stock Hayabusa input shaft.
Here's that bearing with the gear removed. When the Hayabusa's clutch is disengaged, the shaft can be stationary and the gear spinning at engine speed. Hence the need for a needle bearing. In our case, the bearing will only ever see the movement allowed by those springs. A short rocking back and forth motion that's not terribly good for roller bearing durability. We'll likely replace this bearing with a sintered bronze bushing, which should be better at dealing with this kind of motion.
Next, we'll have to connect the shaft to the clutch basket somehow. Problem is, the clutch basket won't fit inside this cover. Not only is this cover too short to contain the clutch basket…
…but it's full of stiffening ribs that surround the giant bearing we use to support the flywheel side of the shaft.
To make this work, we'll have to cut down the clutch basket to some unknown fraction of its original size, leaving enough meat to use a clutch-disc shaped drive plate to connect the basket to the shaft. Then we'll have to design a new shaft that accommodates that bushing under the primary drive gear, a new wedge plate with shorter ribs and a repositioned crank support bearing, and…
…the big bellhousing adaptor plate will have to be changed slightly to allow this flywheel flange to actually pass through it so we can accommodate a new one-piece shaft design.
Designing and building all these new parts is being delayed by the Miatabusa Triumvirate's aforementioned distractions of old houses, zombies and medical parts, but there is at least very reasonable hope it will happen before the end of (this) summer. Having heard this thing run, and having felt the surprisingly tractable torque delivery as it pulled itself up the steep ramp of a flatbed tow truck, we are more motivated than ever to get this thing on the track.
And big thanks to these guys for helping the Miatabusa's slow march of progress:
Apex Speed Technology (tuning…eventually)