Monday, 1 May 2017

Gear Selecter

While putting the kickstart & gear selector case together after the spring incident, I noticed that the selector pawl persistently fell off as I replaced the outer case. With the SQ4, I don't remember having a problem reassembling this complex bit of the gearbox.

Something was wrong.

Pulling the selector apart, I realised that the pin on which the pawl pivots was loose, and that the small springs were not moving freely. Investigation found the pin bursting out of the spring box casting:

In the absence of a better solution, I fixed the pin with Araldite Steel and scraped the spring box enough for the small springs to move freely. At the same time, I searched eBay and put an advertisement on the AOMCC forum:

I never tested the repaired spring box, though I am sure it would have worked (but not for how long). I now have this fine replacement, very kindly provided by Guy Hovey after a plea on the AOMCC forum:

So this is now in place, the box back together and selecting gears again.

The way this works is interesting.
  1. Movement of the gear lever is transferred into the interior of the box, moving a short internal lever (item 37 in the picture below), which has a pin fixed at one end
  2. The pin moves up or down against the small springs, moving the pawl (item 36) about its pivot until they become coil bound. The pawl is now engaged with the selector quadrant.
  3. More gear lever movement then moves the whole spring box against the large springs, which are resisted by the pin screwed into the outer case, behind the gear lever.
  4. The pawl moves the selector quadrant (item 35), changing gear
  5. When pressure on the gear lever is released, the pawl moves back over the teeth cut in the quadrant and returns to the central relaxed position.
The mechanism works in both directions, in the same fashion.

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