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Tightening Loose Gears
The large second gear in the drive train sits on a stub shaft that is integral with the rack driving pinion. The gear bracket is sandwiched between the two gears.
The large gear can become loose on the shaft. If this is happening, support the small pinion on a metal block or anvil, and expand the shaft where it protrudes through the large gear with a centre punch. If this causes the gears to bind to the gear bracket, support the gear bracket either side of the pinion and hit the end of the shaft with a flat-ended drift.

If the rack driving pinion is worn then a new one must be made. Gear cutting is beyond the scope of this website. The large gear is rarely badly worn, but if it is, the same comments
Re-assembly
Re-assembly is the reverse of dismantling. If the knob shaft pinion has been replaced,  you will have to solder the new pinion onto the end of it before refitting the gear frame. The only problem with re-assembly is that it is difficult to solder the washer back on the end of the knob shaft without it getting stuck to the bush in the gear bracket. The best solution is to leave off the washer. Make a strip of thin brass the same width as the distance between the pinion and the side of the burner, and wrap it round the shaft as a sleeve.
Worn Knob Shaft Pinion
If the knob shaft pinion is worn, this is a big problem, as the pinion is too big to allow the knob shaft to be withdrawn from the burner. The knob shaft must originally have been fitted from the inside, before the outer wick tube.
There are only two ways to get out the knob shaft.
1. File or grind down the pinion in situ, then withdraw the knob shaft.
2. Prise out the knob insert and de-solder the knob. De-solder and pull out the bush where the shaft goes through the side of the burner so the shaft can be tilted to one side of the outer wick tube, then push the shaft into the burner. This method is quite tricky, and later burners don’t have a bush that can be removed, just a punched hole with a flange. You will need to get a new pinion made to fit the knob shaft.
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