Engine prop shaft adapter

The Hayabusa engine normally has a toothed gear to transmit the power from the gearbox to the rear wheel of a motorbike. Wesfield in their cars mount a special adapter on the gearbox output shaft that adapts it to a split Sierra drive shaft. The adapter is normally made of mild steel and is rigidly attached to the gearbox shaft via a large M20 lock nut and a large washer. If you trawl the forums this nut comes undone with amazing regularity. Mine unwound at Croft on 7th June 2014. It was trailered back home as I had no chance of repairing it at the trackside. The mild steel adapter was badly damaged and I did not want the gearbox shaft to go the same way.

I took the advice of Andy at AB Racing. He has a special adapter made to his exacting requirements which is reported to solve the problem. It is designed to be loose fit on the gearbox shaft unlike the Westfield part and is made of hardened steel.

It is unfortunately about 10mm shorter than the original Westfield part so I had to make an alloy spacer in the lathe to make it all fit back together.

The M20 nut was also modified to make the adapter a loose fit on the shaft and I tightened it up such that it will not come off again. I used the permanent nut thread fluid to bond it up tight.

I have no idea if this will permanently solve the problem but is seams like a good approach. Time will tell.




Westfield adapter after failure

Gearbox splines

10mm custom spacer



Nut modified on right to remove some of the step



Reassembled

Update 11th Sept 2014

Kept a regular eye on this part of the car and it regularly gives an 1/8-1/2 turn between race events on the cap head screws no evidence of the 32mm nut loosening again. I decided to wire the bolts to ensure they don't come loose again. I drilled the cap heads in place using some carbide burrs (long job).