Thread : BSC vs BA ?

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Thread : BSC vs BA ?

Post by FGF » Fri Jul 17, 2020 1:59 pm

Hello ,

I was looking for the oil pump screws (41-0609) which are made with a BSC thread.
A supplier change them by the breather head screw ( 40-0309 ) with a BA thread and a larger slotted head.

These two threads are very close ...
but does someone has used any BA in a BSC thread with a good fortune ?

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Re: Thread : BSC vs BA ?

Post by crankbuster » Fri Jul 17, 2020 3:07 pm

I think that 2BA and 3/16 BSC are interhangeable.
Certainly BSA & Triumph did, if you compare the B25 with the TR25 parts books. You see that the threaded rocker spindles (with the same part number) can use both, BSA BA, Triumph BSC:
BSCBA.jpg
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Re: Thread : BSC vs BA ?

Post by eebtr7 » Fri Jul 17, 2020 11:11 pm

Would some good soul please explain to this antiquated, more or less demented brain why BSA and Triumph used different part numbers on the B25 and TR25 when the same machines were built in the same building, on the same assembly line track, with 98% of the same parts? In the above illustration, the rocker spindle is a good example.

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Re: Thread : BSC vs BA ?

Post by kommando » Sat Jul 18, 2020 7:10 am

2 sets of dealers, 2 engineering offices, 2 part numbering systems, uncommon parts, common parts etc etc.

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Re: Thread : BSC vs BA ?

Post by hhh » Sat Jul 18, 2020 6:52 pm

Isn't BSC 60 degree and BA 47.5 degree thread angle? That's about as bad a mismatch as possible.

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Re: Thread : BSC vs BA ?

Post by beat » Sat Jul 18, 2020 8:44 pm

hhh wrote:
Sat Jul 18, 2020 6:52 pm
as bad a mismatch as possible.
= english masterpiece :!:

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Re: Thread : BSC vs BA ?

Post by Jeff K » Sun Jul 19, 2020 3:57 am

Yes
BA is 47.5 degrees and BSC is 60 degrees.
screw5.gif
screw5.gif (4.11 KiB) Viewed 845 times
bsc.jpg
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Re: Thread : BSC vs BA ?

Post by Jeff K » Sun Jul 19, 2020 4:58 am

It has been a long time, but I seem to recall one of the "butcher Job" quick fixes was to use a 10-32 screw in place of a 2BA.
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Re: Thread : BSC vs BA ?

Post by Canberra » Sun Jul 19, 2020 10:09 am

I remember that one Jeff. The 10-32 is 60 degree, similar size and works well as a bodge for worn threads. Slightly less TPI but wouldn't be noticed on a standard 2BA nut. Although I doubt if you'd find a deep thread to be tightened into before it becomes a bind.

I remember when I worked in a metrology lab many years ago chucking out boxes of screws supplied from the supplier with stretched threads so unless you have a profile screen to view and measure most of us wouldn't know what crap is supplied even by the big companies.

John

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Re: Thread : BSC vs BA ?

Post by beat » Sun Jul 19, 2020 8:42 pm

why not creating a new, - better tread ?
BSACB named, and with a angle of 53.75 :?: :?: :?:

:thumb

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Re: Thread : BSC vs BA ?

Post by Jeff K » Sun Jul 19, 2020 9:17 pm

I also seem to recall that the 10-32 will fit a odd Japanese JIS thread, the M5 x .8 used up until 1968. Sadly after all of these decades of working on motorcycles, I have a huge collector to Taps and Dies. Many are very obsolete.
Jeff

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