Gearbox Studs | Scotts Owners Club

This topic has 2 replies, 2 voices, and was last updated 15 years, 5 months ago by Maurice.

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2nd November 2007 at 6:25 pm #1996

Maurice
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My 1934 bike apparently started life with a hand gear change. At some time this has been converted to a foot change. I suspect it was a home made modification for the angles of the linkage are poor. Despite my best efforts the gear change is unacceptable and the linkage becomes loose after a very short ride. Whilst wishing to remain authentic I have reluctantly decide to fit a newer box which came with the bike. This box has a nice casting on the end cover to take the gear change unlike the original which has a plate bolted onto it.

This long tale brings me to my questions. The old box has two studs with which to secure it to the gearbox undertray. When I tried to transfer these studs to the newer box I found the threads were different.

1. Can anyone tell me what thread is likely to be on the newer box?
2. Might it possibly be held in place by two bolts rather than studs and nuts? This would certainly ease removal.
3. The fore and aft adjuster goes around one stud only, effectively tilting the gearbox forward. Should there be a spacer on the forward stud.
The original box has a flat bottom there are two raised spacers on the newer box.

Any comments appreciated.

2nd November 2007 at 9:37 pm #7081

BRIAN MARSHALL
Participant

Hi Maurice. Earlier handchange boxes and 1930’s footchange boxes have three eighths Cycle thread studs (26TPI), and later boxes, including Birmingham boxes, have three eighths BSF bolts, which make removal and installation of the gearbox much easier. Be VERY CAREFUL that any new bolts, when tightened up, do not protrude into the works, or you will have a major disaster on your hands!! The only drawback to bolts is that oil does tend to seep down the threads, so use PTFE tape on the threads when installing. Obviously you can use Cycle thread bolts instead of studs on the earlier boxes. Do use the correct large diameter washers to spread the clamping loads on the alloy tray, or a steel plate about 4″x1″, which is even better if you are not concerned about originality. Hope this helps. Regards. Brian Marshall.

4th November 2007 at 11:25 am #7082

Maurice
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Thank you very much Brian, all that I needed to know.
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