Project Miatabusa Gets the Shaft!

miatabusa gets the shaft lead

Project Miatabusa Gets the Shaft!

by Dave Coleman

The last time any of you heard anything but excuses about Project Miatabusa was January. I almost can't believe that myself. The excuses? Well, we were busy… I was busy winning a LeMons champoinship and then enjoying the spoils of victory. Tim (who supplies all the actual talent for this endeavour) was busy putting a CBR1000 engine in the Angry Hamster. And Alex, who's really good at talking the rest of us into doing silly things like this, was busy trying to talk us back into finishing it. 

It finally worked.

Hayabusa gearbox

To re-cap just a bit, the idea was to take the Hayabusa's relatively fragile transmission (it'll pull a car around for a while, but before long things start breaking from the substantial extra load) and replace it with a shaft that holds a Miata flywheel. That's pretty simple to say, but actually doing it… 

miatabusa cad drawing

To turn the idea into reality, Tim designed a complex, 4-piece Hayabusa-to-Miata adaptor. If you never saw these before, you REALLY need to go read the first few parts of this project to get up to speed.

Miatabusa hayabusa flywheel shaft

And there it is, just as easily as we said it, Tim made it. Ok, not quite as easily…

To understand just what you're looking at, we've got to walk through how everything works. With the original shaft, on the left, the giant gear is driven directly off the crank. That gear carries the Hayabusa's multiplate wet clutch, and when the clutch is disengaged, the gear spins freely on the shaft. That detail will be important later. The small gear next to the giant one is the drive gear for the oil pump. Next up is a bearing, then 1st gear, 5th gear, 4th gear, 3rd gear, 6th gear, 2nd gear, and finally another bearing.

Look closely at the new Miatabusa shaft and you can see we moved the big bearing to the other side of the gear. This puts it halfway between the gear and the flywheel, two things that really should be well supported.

The oil pump drive gear is actually a separate part from the main drive gear. It sits on a loose spline and is normally held in place by the bearing. Tim threaded this portion of the shaft so the gear could be held in place by a threaded collar.

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