At the weekend I took the boxes and degreased with acetone.

Then ran them at 4.5 volts for 8 hours submerged in rubbing compound (coarse). Then degreased and ran for 4 hours in motor oil. Degreased, oiled them again on the bushes and then greased again (heavily).

I adjusted the pinion until there was room for a sheet of paper between the teeth of the pinion and the first cog in the gear train.

And they still clatter. I admit it is deadened somewhat by the thick grease but its still louder than one would expect.

There are no burrs or anything on the teeth. The wheels are not touching each other.

Looking at it carefully I see no major problems at all.

I did read before that the gears should spin for a few seconds just by turning by hand if they are properly "broken in " (a concept I am rapidly losing faith in).

But they are physically impossible to turn by hand from the drive shaft end with the motors attached. So unless the "spin freely for a few seconds" refers to a motor-less situation.......... I dont see how that condition can possibly be achieved.

At the risk of starting a storm of abuse......I also spoke with a buddy who fixes clocks and he maintains that grease on brass gears is a bad idea if the box cannot be sealed against dust and grit and they should be run "dry" except for some lubrication on the bushes/bearings.

Admittedly a clock is different to a gearbox but should I be heavily greasing brass gears or not?

Beraring in mind that I can 1) never seal these boxes, 2) can never seal the tank entirely against dust and grit and 3) dont want the boxes to accumulate what would in effect be an abrasive sticky mixture.

p