Puch VZ50 Pedal Modification

As a moped "trying" to be a motorbike, the VZ50 left pedal could be orientated like a bicycle with the cranks 180 apart, or it could be swung round 180 to create two level pedals.

However to make the change, it was necessary to remove a cotter pin to disengage the simple dog clutch to choose the pedal position.

Thumb wheel pedal system

The modification here was to enable either pedal orientation to be used but without the need for tools to make the change.

The idea being the bike would be run with level pedals most of the time, but could be converted to "pedaling mode" easily, if it was being difficult to start for instance.
In addition, on this particular bike the left pedal was not held very securely with the cotter pin. The pedal drooped at a sad angle and wobbled a lot during riding.

The drawing below shows the new part. It was a simple thumb wheel but with a thin knurled area to avoid catching the rider's trousers or ankle.

The only critical dimension was the 25mm boss at a length of 10mm. This would be the  working face that would clamp the pedal hard against the dog clutch when tightened.
The cavity on the inside was just for clearance about the axle.

The thumb wheel was turned on the lathe and drilled to take a length of threaded rod. This was then silver-soldered into place.

Thumb wheel and drilling guide

To fit the thumb wheel to the bike the axle had to be drilled and tapped with a matching M6 thread. To ensure the hole was drilled centrally, a guide bush was made up to be a snug fit in the pedal.

This guide was drilled for a 5mm drill.
It was then opened out to 6mm to help guide a tapered M6 tap in.

Drilling the axle 5mm using a guide

The final assembly looked OK and worked fine.
There was no issue with it catching the rider's leg during pedaling.

Done up finger tight it remained secure for a decent test ride.

In hindsight this modification has not been that useful. The bike starts surprisingly well even in the winter months from just a single push on the pedals; so there is yet to be a need to restore the pedaling mode.
However it is a nice feature to have on the bike.