Restoring an original rev-counter reduction gearbox

This gearbox was screwed to the dynamo when I purchased TA0844. It had a circular tag under one rivet, engraved with the words: REDUCTEUR R=100/266 COTE REDUIT. It was made from Mazac or something similar. The input and output shafts were Yeager Tube, with the input shaft having a short attachment to convert it to key drive for the dynamo armature end.

Photo 1: “everything fell apart”.

As can be seen from Photo 1 the gear casing was distorted and cracked in many places. The two rivets holding the cover were also holding the bits together. When these were removed everything fell apart.

I made a new case from stainless steel. The case dimensions were the same as the original except for the thickness of the input face which I made about three mm. The input spindle housing or tube, was made to be an interference fit in the case with a thin rim or flange to locate it at right-angles when pressed in. The outside edge of the flange (inside the box) was chamfered to allow easy rotation of the gear. Instead of rivets, I used two 4BA screws to hold things together.

The cover with the output spindle was warped and cracked. When screwed to the case it split almost in half. I made a cover of brass with a reduced thickness edge to fit the case and provide a grease seal, and a similar output spindle tube to the input, but with a larger flange, also chamfered. The cover thickness was 2 mm thick and being brass, the tube would not be a mechanically sound fit with the arrangement as for the input tube. I made a ring collar to fit on the outside of the housing to ‘lock’ the spindle in place with an interference fit. Once again these were made from stainless steel, when pressed together the flange and collar sandwiched the brass cover.

Photo 2: the various components before assembly.

The various components are shown in photo 2. Photos 3 and 4 show the completed gearbox with grease nipple fitted, hardly original, but looks good.

Photos 3 and 4: the completed job.

Bob Butson
June 2011

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