Puch VZ50 Pedal Modification
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.
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.
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.
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
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.
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.