Hitchcocks Forum

Afternoon all,

Quick question - I wish to replace the bolts that attach the outer gearbox cover to the inner on my 4 speed box. However, I'm not sure what thread is used. Ideally I want to replace the slot heads with an allen or hex head.

Thanks,

Andy

They are likely to be 1/4 Whitworth. I personally like the slotted heads its the classic English look and they aren't anywhere near so easy to over tighten. There is a fetish for replacing with cap screws and stainless Nylock nets which I think is a pity but each to their own I suppose.

I believe they are BSF which is also similar to BSC but you can get away with Whitworth, thread pitch isn't quite the same but will do

1/4 BSF is 26 tpi like cycle and 1/4 whit is 20 so you can't interchange them without grief. Im pretty sure the threads into alloy are whitworth on the Albion and its copies as are the ones on the rest of the pre metric Bullets.

Hi Simon, this is what info I have from the "Nuts and bolts of the matter", an article written about the thread types Occasionally you might turn up BSC or CEI taps in second hand dealers or at swap meets. Generally these won't be worth bothering with because they will be carbon steel, old and worn out. Other Whitworth form threads that have pitches corresponding to BSC or CEI are as follows
3/16th BSF equilavent to 3/16th BSC,
1/4in BSF equilavent to 1/4in BSC
9/32 BSF equivalent to 9/32 BSC
1/8th Model engineers equivalent to 1/8th BSC
7/16th Model Engineers equivalent to 7/16th BSC
1/2in Model engineers equivalent to 1/2in BSC
Small screws and nuts on non cycle parts, carbs and electrical components for example will generall (not always) be British association (BA) threadsBA thread form is generally similar to Whitworth but has an included angle of 47.5 degrees. The Ba series of threads was intended as a combination of the BSF series. It is an imperial thread but with a decided metric influence.
In other words Whithworth will be good enough for the gearbox cover lol

Just take one to aNut&Bolt place, they will tell you and sell you the replacements, dont think it good to use Hex. heads in this application

I am very fortunate to have a brilliantly equipped friend who has BA, BSF, and Whitworth and Metric medium and fine taps and dies all sharp and fresh.You can still buy them from Trade Tools over here although some are getting a bit hard to find now. I remember my Dear Old Dad was restoring a Riley 9 Tourer a while back and we need to make some wheel nuts for it which were left hand thread on the left hand side. We thought we were buggered but when we asked Trade Tools for a 9/16ths BSF left hand tap the bloke said first second or plug? Having a lathe makes single point cutting possible for most things but the very small stuff and internal threads below 1/2 are a bit troublesome.
This is a good chart I found on line http://www.gerardsgarage.com/supportfil ... Tables.pdf

The 4 speed gearbox main and inner cover screws, Indian and Redditch use 1/4" bsw (british standard whitworth) as Simon says. DO NOT try 1/4" bsf or bsc as these are completely different and will ruin the threads in the cases.



1/4" bsf and cei are both 26tpi but one is 55 degree thread angle and the other is 60 degree, but with the 1/4" whitworth, this has only 20tpi. Norm is getting confused between a whitworth thread form and british standard whitworth which are 2 different things.
Chev