Moped Luau: Puch ZA50 Clutch Rebuild Part 2: Second Gear

Thursday, September 27, 2012

Puch ZA50 Clutch Rebuild Part 2: Second Gear

My second gear clutch was surprisingly in great shape compared to my first gear clutch. The clutch shoe lining were all intact and not cracked. I previously lightened the shoes without taking them apart by drilling numerous holes via a drill press. (Note: Optimal location to lighten the clutch shoes is along the outer edge as shown below because it has the most "metal mass" that can be removed. Also, you want to take out the most "metal mass" toward "that side" of the linkage hole pivot point to optimize the "lightening" effect on the clutch. The outer edge of the pivot point has the most mass that produces the centrifugal force which the clutch shoes needs to generate to overcome the centripetal force created by the clutch spring. When this happens the clutch will engage. Less mass on the shoes means you need more angular velocity to generate the centrifugal force. Hence, the clutch shoes will engage at a higher RPM giving you that longer "stall". Anyway, enough physics!!) As I did with the first gear clutch, I banged out the linkages:

All blown up!!

I weighed each clutch shoe to see how much mass I previously took off. I re-drilled some of the holes to balance all shoe weights.

On the dot!!

For the modification, I opted to only do a spring replacement. I decide to go with a 20# Tomos spring (uncut). A new Tomos spring is much more stiffer than a stock ZA50 spring. And since the shoes were already lightened and the clutch assembly will be reinstalled "flipped", this combination should be enough to provide the "stall" and "downshift" in and out of second gear.