How To: Excelsior rear hub Cushion Sprocket
Excelsior Cushion Sprocket
Excelsior offered a Cushion Sprocket, which used coil springs to dampen out the vibrations that the motor transmitted through the drive train. Remember that this was about 10 years before crankshaft shock absorbers became common. While belt drive bikes had a smooth feel due to the belts absorbing vibrations, the chain drive bikes were less comfortable…
X’s solution was to let the sprocket float between two plates that were locked to the rear axle. The sprocket was free to rotate relative to the axle, but while rotating it would compress 6 springs. This would take up some of the shock, then the springs would push the sprocket to rotate it back into its relaxed position. Of course, this happened many times per minute as the power pulses were delivered from the pistons, through the chain, to the sprocket.
The springs in my X were tired and broken. Square section springs are available from tooling shops, as used for die presses. I bought a set of springs from MSC that had a spring rate that seemed to approximate the old ones. Fitting them was a simple plug and play ordeal.
The MSC part number is #07660590 The link is here.
With the brakes and Cushion Sprocket sorted, once again I had to fire up the lathe to make some new shafts and nuts. That crack in the hollow tube axle worried me, but it wasn’t under much stress due to the solid axle that runs inside it. But I made up a new part from 4140 chrome moly anyway. Straightforward lathe work, and a quick session on the mill to cut the groove on the end for the lock washer. Then a large hex nut and a special round nut with grooves, as shown in earlier posts. Please do yourself a favor, if you have these types of nuts on your old bike, don’t use a hammer and screwdriver to tighten/loosen them! It will work ok for a few times, but eventually the nut will be destroyed. And the next owner of the bike will curse your name….
I popped it all back in the bike, and it did fine on the ride from Atascadero to Creston and back. Now to start carving a wooden brake for that Premier…