I imagine this solves the thread angle question. https://britishfasteners.com/threads-bsc
ET: Engine (Twin) Black Shadow Crankcase Threads
- Thread starter RayF
- Start date
Nope, its not on the list.
Sorry Roy,
the 20 TPI series in BS811 are 60 degree, UNTIL they get to 7/16"-3/4" from when on they are Whitworth form; 55 Degree.
Nope, I don't know why either, but it's there in black and white.
Delboy is correct. If you look up BS811 which is the British Standard for all cycle threads and look at table 14 & 15 on pg 15 (from the page numbers printed on the page or pg 21 of the PDF) you will see the 9/16" thread we are discussing.
That's probably why you can have issues with new studs if the thread pitch is 60 deg and not the correct 55 deg........many damaged threads, and many times it can happen if the original studs are not used......On early engines that originally used the 2 piece stud/tube arrangement, it is common for the upper section of thread in the cases to feel a bit "Sloppy" this is because the upper section of thread has been over tightened at some point and damaged the upper thread section.......with the lower part having the small brass insert, once removed this section of thread seems fine........It is a double edged sward to leave this and rely on the existing thread to handle the load.......The repair is not easy, unless you are clever enough to custom make new studs........time consuming and expensive......i feel the 5/8" UNF studs that Maughan's make is the best and quickest method.......I resist welding these cases unless absolutely necessary........distortion and annealing the surrounding alloy is not good.
Sorry Simon, when I wrote the 60 deg for the cylinder studs I had a nagging doubt in my mind so I checked again, but obviously not the larger sizes.
I made my titanium studs over 20 years ago and must have looked in KTB and used the Whitworth form (55deg). Titanium is interesting as it stretches slightly so is probably better for things like cylinder studs.
I made my titanium studs over 20 years ago and must have looked in KTB and used the Whitworth form (55deg). Titanium is interesting as it stretches slightly so is probably better for things like cylinder studs.
not a 5/8" stud all the way down, the bottom thread of the stud only.
Today I learnt that bicycle pedals are still most commonly 9/16 by 20TPI (but 60 degree).
https://www.lprtoolmakers.com.au/cycle-thread-bscy-20tpi-tap-sets-7-16-to-3-4/
Another of the places metric dare not tread.
https://www.lprtoolmakers.com.au/cycle-thread-bscy-20tpi-tap-sets-7-16-to-3-4/
Another of the places metric dare not tread.
Last night I checked my Argentinan two part cylinder studs with microscope, they were 60 degrees thread form definitely, 9/16 x20 , the tap I got for cleaning up engine threads was marked UN 9/16-20. So no, not 55 degrees here.
As to titanium cylinder studs, I did not have the courage to have that material for this, loads are tension and my gut feel is the ht type looks a bit brittle. So it was stainless for studs and M 10x1 resp. 10x1.5 for stud ends, stainless very tough, no brittleness but you have to have MoS2 paste or the like on threads, even more critical on titanium threads I guess ?
Funny with bicycle threads same cycle threads for a century still. But it is a weird business anyway, always was, with all sorts of threads you won´t find anywhere else. Seems they are even more "conservative" than in the rest of engineering. But for no rational good reason having imperial sizes. Allright, once the production line is set up it does not matter much, if metric or imperial. But in a small workshop for one-off jobs it is just a waste of time in the awkward imperial manufacturing system.
Vic
As to titanium cylinder studs, I did not have the courage to have that material for this, loads are tension and my gut feel is the ht type looks a bit brittle. So it was stainless for studs and M 10x1 resp. 10x1.5 for stud ends, stainless very tough, no brittleness but you have to have MoS2 paste or the like on threads, even more critical on titanium threads I guess ?
Funny with bicycle threads same cycle threads for a century still. But it is a weird business anyway, always was, with all sorts of threads you won´t find anywhere else. Seems they are even more "conservative" than in the rest of engineering. But for no rational good reason having imperial sizes. Allright, once the production line is set up it does not matter much, if metric or imperial. But in a small workshop for one-off jobs it is just a waste of time in the awkward imperial manufacturing system.
Vic
