Thread types

[Steve64]

Hi guys, this may sound like a silly question but what threads were used on the mid 40s bikes, I have ben told BSF and BCY,(BSC) similar threads but slightly different cut. I need to purchase a few taps that cost a small fortune for each and would like to order the correct ones. Any help greatly appreciated.
Thanks , Steve.

[SPRIDDLER]

BSF is generally used for threads and studs going into alloy castings and BSC (British Cycle) for frame/cycle parts. I would say that Whitworth thread is the most common on our old bikes. It's common the a stud will have BSF on the end that goes into say an alloy crankcase but Whitworth at the other end for a nut. BA threads are also found - mainly on electrical equipment (dynamos, switches plus the end cover plates on the singles oil pump) but it's unlikely they'll ever need to be tapped out on electrical equipment .

Shame you're not in the U.K. as loads are available cheaply at autojumbles.

This info in the 'Tech Articles' section will help you.

https://www.jampot.com/article_read.asp?id=391

[Steve64]

Thanks for your reply , it sounds like I may need a bit of everything but at least i know now what to start collecting if and when I do come across them.
Thanks again for advise, as usual invaluable.
Cheers, Steve.

[Pharisee]

Tracy Tools stock just about every tap you can imagine and their delivery is excellent. If you're only buying taps to clean out existing threads, you don't necessarily need expensive HSS ones. A cheaper carbon steel tap will do.

[Groily]

Tracy Tools stock just about every tap you can imagine and their delivery is excellent. If you're only buying taps to clean out existing threads, you don't necessarily need expensive HSS ones. A cheaper carbon steel tap will do.

+1 for that.
Their 'loose sets' of two taps per size, plus die, in BSF, BSW, BSC, BA etc, at £20 a pop in the sizes we need, are pretty OK. I've used them for ages, saving a bit of hard-earned for HSS kit in sizes I need regularly for cutting fresh threads.
https://www.tracytools.com/product-cate ... -and-dies/
Because they come loose, no wasted weight or postage cost on packaging or tools either.

[Joker_Bones]

I would say that Whitworth thread is the most common on our old bikes. It's common the a stud will have BSF on the end that goes into say an alloy crankcase but Whitworth at the other end for a nut.

Is that the case for '40s bikes? All the bikes I have worked on are '50s and '60s but I can't think of any Whitworth threads on them.
As you say... BSF into ally but, with a few exceptions, the remainder have been BSC.

[SPRIDDLER]

Is that the case for '40s bikes? All the bikes I have worked on are '50s and '60s but I can't think of any Whitworth threads on them.
As you say... BSF into ally but, with a few exceptions, the remainder have been BSC.

You've got me thinking now, JB. I mostly use Whit spanners and sockets on the engines and gearboxes of my ex '47 Ajay and current '54 Matchless.
TBH I just pick up the spanner that I habitually use for that particular job without looking at what it is marked and without giving a thought to the thread form of the fixing. I've always assumed, perhaps naively, that a fixing requiring a Whit size spanner has a Whit thread form.

[Groily]

Ha! Thinking can be a risky biz Neville. But - the thought's not essentially wrong.
Whitform (hybrid sort of word) about covers it, as BSF and BSW (and I think one or two other thread forms maybe) come under that heading. Just a Q of tpi, but all 55°as opposed to other thread angles, and I'm sure there's stuff on roots and crests and all that good stuff too.
BSF was developed to provide heavier / stronger core diameter than the coarser original 'whitworth' offered, and I guess more contact area between bolt 'n 'ole/nut.
Same spanners fit Cycle nuts and bolts too of course . . .
So, there's loads of whitform on our machines, and loads of 60° BSC at 26tpi, some at the alternative 20tpi in larger sizes, and there's BA at 47 'n a 'arf. Most of the whitform as we might now call it is BSF - but some fasteners into aluminium are in fact BSW. Studs with 1/4 x 20 tpi (BSW) one end and 1/4 x 26 t'other (60° BSC or could be 55° BSF to the naked eye just to confuse) aren't rare on AMC stuff (and are common on a lot of other marques).
In terms of tap and die usage on 'our' bikes, BSF and BSC are the main men, but a few BSW things may be handy, and a bit 'o BA for the 'leccy side as you said originally (also, for Twin owners, for timing cover screws, at a ridiculous 2BA into ally - no wonder so many timing side crankcases have trouble there).

[SPRIDDLER]

Thanks Bill. Thinking about it (for the first time in 60 fettling years), I'm pretty sure I use a Whit spanner on my single's rocker cover bolts which have a 5/16" BSF thread form.

[Joker_Bones]

And... British Standard Pipe (BSP) on the oil and petrol fixtures and fittings.