Simon, I'm not aware that any of our suppliers stock replacement bushes.
My local small machine shop turned up a pair for me from phosphor bronze. The bore will shrink very slightly once pressed into the gear cluster, but the fit on the shaft was still only fractionally tight - maybe I was just lucky. I 'adjusted' clearance by running a honing tool down the bore in an electric drill, lubricated with light oil. This was in 1995 and it's still going strong.
I'd suggest assessing the condition of the shaft before going to these lengths, it may stand a light grind to address uneven wear; then bushes can be sized to suit.
When all is assembled and tightened up you should have about 5 - 10 thou of end float (n.b. it will be about 5 thou more at running temperature). Shim as necessary.
I guess option 2 is find another gearbox - they are still fairly cheap and plentiful - but it may well have the same issue. The wear is principally due to the axial force generated by the single helical gears.
My local small machine shop turned up a pair for me from phosphor bronze. The bore will shrink very slightly once pressed into the gear cluster, but the fit on the shaft was still only fractionally tight - maybe I was just lucky. I 'adjusted' clearance by running a honing tool down the bore in an electric drill, lubricated with light oil. This was in 1995 and it's still going strong.
I'd suggest assessing the condition of the shaft before going to these lengths, it may stand a light grind to address uneven wear; then bushes can be sized to suit.
When all is assembled and tightened up you should have about 5 - 10 thou of end float (n.b. it will be about 5 thou more at running temperature). Shim as necessary.
I guess option 2 is find another gearbox - they are still fairly cheap and plentiful - but it may well have the same issue. The wear is principally due to the axial force generated by the single helical gears.