Quoting Richard Wood:-
"Helical timing gears are a lot quieter and really a must. Velocette tried straight cut in the 50's when they introduced the M series. It was found acceptable on prototype engine but the thinner timing cover on production models forced them to use helical gears which solved the problem".
I know helical gears would be quieter but they also impose axial loads on the shafts and/or bearings on which they are mounted, and these loads would have to be accomodated in the design of the complete set-up.
I believe, if the timing cover (it would obviously have to be the early type without the cooling slots) were to be made oil tight by means of a gasket and provided with a filler plug, a drain plug and a level plug so that the lowest gear (i.e. the gear on the crankshaft) could be up to half it's diameter in oil, the gears would then be running in oil.
I believe this would reduce the noise to an acceptable level but this would need to be proven.
