I have been thinking about this for some time and a fellow forumite said he could try it.
the objective is to take a new HG Shimano 7 speed freewheel
and narrow it down to be 24mm thick 6 speed.
I have 120mm spaced junior road bikes that are 5 speed- it would be great to built them to be 6 or possibly even 7.
yes I hear you -it sounds quite easy to respace to 126
or throw in an Ultra-6 suntour freewheel.
well I have tried it and the ultra 6 just does not work.
a regina 5 freewheel is 25mm outside cog to outside cog,
the ultra-6 is 27mm
a junior road bike(JRB) has such a short distance between the bottom bracket and the rear axle that the chain just cant flex that much-
yes I hear you- I have tried a 7 speed, 9 speed and 11 speed chain.
I looked at an old 9 speed casette I had lying around and noticed that 6 cogs outside to outside are 24mm!
now the HG freewheel has the same thickness cogs
cogs are 1.8mm thick and spacers are 2.6
so a 6 speed with narrow cogs should be something like this-
1.8 x 6= 10.8
2.6 x 5 = 13.0
total is 23.8
the 7 speed,6 speed and 5 speed HG bodies avail are all 31-33mm wide assembled
this wont do- 27 is the max I can go on this.-it just wont fit.
idea is to mount it up on the lathe and turn off the threads, and make new deeper threads,
and new shims at 2.6 and see how it goes.
any thoughts on this project are greatly appreciated.
and then again if it does work I hope we can make more- even a narrow 7 could be assembled with just shim swapping