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Gearbox backlash

Posted: Sun Jan 28, 2018 10:44 am
by Gannet
I am rebuilding a couple of the small 10:21 gearboxes of FV/LM/SJM model type and would like some advise as to how much gear backlash to set.
I have been advised in the past to shim the prop shaft so that the gear meshing feels 'nice'. Well, these gears are 60+ years old with some of the expected corrosion and pitting damage, so 'nice' is not what they feel. But apart from that there must have been a factory build and also agent rebuild instruction to set a specific backlash tolerance.
I have provisionally rebuilt them with 0.012 as measured on the end of the prop shaft.
But what is the correct specification? Can anybody advise me?
Thank you.