Gear ratios

[John.Newbury]

I have a 1956 NH with a 57 GB44 gearbox which I believe is the gearbox fitted to the FH, does anyone know if the gear ratios are different FH to NH and if so any ideas how they differ?

[pete.collings]

The gear ratios should be the same as a GB39 gearbox which would originally have been fitted to a late NH, and would have exactly the same internals as a GB 44 box (and virtually all the other GB boxes, although the mainshaft lengths could differ dependent on the model/year).
The gearing was changed via the engine sprocket, a NH having a 19t sprocket and a Huntmaster a 24t sprocket.
It was only in the HT trials boxes that there were different gears to accomodate the lower gearing that trial bikes needed.

[John.Newbury]

Thanks Pete that's reassuring. I seem to have te correct main shaft as I have the enclosed chain case and everything fits!