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#374648 - 05/22/11 4:00 pm BSF and BSC  
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Hi guys. Just a random thought, but how do you guys distinguish between BSF 1/4-26tpi and BSC(or CEI)1/4-26tpi? For example, the rocker box nuts, the steering stem securing bolt and the brake arm stopper bolt for late rigid model are all 1/4-26tpi but I'm not sure which pattern is used. In addition to this, what is the difference between BSC and CEI? I know they are 60 degree but I don't know more details.

Thanks,
Machico

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#374656 - 05/22/11 4:54 pm Re: BSF and BSC [Re: machico]  
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DMadigan Online content
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I do not have my Machinery Handbook handy but I believe BSC has a 47.5 degree tooth form.

#374657 - 05/22/11 5:17 pm Re: BSF and BSC [Re: DMadigan]  
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Originally Posted By: DMadigan
I believe BSC has a 47.5 degree tooth form.


I think the thread angle of BSC is 60 degree. The thread angle of BA is 47.5 degree.

Thanks,
Machico

#374659 - 05/22/11 5:51 pm Re: BSF and BSC [Re: machico]  
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Hi Machico,

Originally Posted By: machico
distinguish between BSF 1/4-26tpi and BSC(or CEI)1/4-26tpi?
the difference between BSC and CEI?

BSF has a 55-degree included angle in the triangle formed by each thread peak or trough; otoh, as you've said, Cycle has a 60-degree included angle. Nevertheless, in general, it's almost impossible on decades-old parts.

However,:-
Originally Posted By: machico
For example, the rocker box nuts, the steering stem securing bolt and the brake arm stopper bolt

... when you know that, as a general rule, Triumph and BSA standards were BSF threads into aluminium alloy and Cycle threads into/on iron and steel (including nuts on bolts and screws), then you can make an educated guess depending on the component.

That said, the fun starts when you get a 1/4"-dia. stud that screws into an alloy component and takes a nut on the other end - both ends will be 26tpi but which end is BSF and which is Cycle? grin

Finally, bear in mind also there's BSB - British Standard Brass - thread. 26tpi at all the diameters Cycle is, but 55-degree included angle. smirk

Hth.

Regards,

#374681 - 05/22/11 9:28 pm Re: BSF and BSC [Re: Stuart]  
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Hi Stuart

Originally Posted By: Stuart

Originally Posted By: machico
For example, the rocker box nuts, the steering stem securing bolt and the brake arm stopper bolt

... when you know that, as a general rule, Triumph and BSA standards were BSF threads into aluminium alloy and Cycle threads into/on iron and steel (including nuts on bolts and screws), then you can make an educated guess depending on the component.


This is very interesting. I didn't know that. So, the parts I listed as an example are all cycle thread right? Are there any source of this rule?

Is this because aluminum alloy is more fragiler than steel? I'm just guessing but it seems that the thread of BSF is deeper than cycle thread and the deeper thread may be better for fragile material? Am I correct?

Originally Posted By: Stuart


That said, the fun starts when you get a 1/4"-dia. stud that screws into an alloy component and takes a nut on the other end - both ends will be 26tpi but which end is BSF and which is Cycle? grin


In this case, I will ask you which is which. grin
But are there any studs like that for Triumph? The 1/4 studs for rocker box have a BSW 20tpi and a BSC(CEI?)26tpi on the other end. I thought the 1/4 studs for the oil pump are same pattern as rocker box studs.

If the length of the thread is different from each side, it is easy to distinguish though.

Originally Posted By: Stuart


Finally, bear in mind also there's BSB - British Standard Brass - thread. 26tpi at all the diameters Cycle is, but 55-degree included angle. smirk


Oh no. I didn't know this either. It's so complicated!! Is BSB pattern used in Triumph model?

Thanks for your very informative post!

Machico

#374688 - 05/22/11 9:54 pm Re: BSF and BSC [Re: machico]  
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BA, BSC, BSF, BSP, BSTP, BSW, CEI, UNC, UNF, ME, BSB.


http://www.britishfasteners.com/threads/

#374767 - 05/23/11 8:47 am Re: BSF and BSC [Re: L.A.B.]  
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Thanks for the website! laugh

Thanks,
Machico

#374823 - 05/23/11 4:09 pm Re: BSF and BSC [Re: machico]  
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Hi Machico,

Originally Posted By: machico
For example, the rocker box nuts, the steering stem securing bolt and the brake arm stopper bolt

Originally Posted By: Stuart
Triumph and BSA standards were BSF threads into aluminium alloy and Cycle threads into/on iron and steel

Originally Posted By: machico
the parts I listed as an example are all cycle thread

A lot of the time; as I said, "you can make an educated guess".

Originally Posted By: machico
Are there any source of this rule?

There probably was at some time somewhere; I just know it by observation.

Originally Posted By: machico
Is this because aluminum alloy is more fragiler than steel?

Ime, not generally at the torques used on motorcycles. If the designers were that worried, imho they'd have used a coarser thread into aluminium. After 1968, when BSA and Triumph changed to Unified threadforms, they used UNC into alloy; if they'd been worried before, they'd have used Whitworth (BSW) which is the same tpi as UNC for each diameter (except 1/2"). Problem with a coarse thread on something that vibrates (not that British singles and twins vibrate much whistle ) is it takes less rotation to loosen than a fine thread. frown Subsequently, the Japanese used metric coarse threads, which aren't that dissimilar to BSF threads at similar diameters (e.g. M5 31.8tpi, 3/16"BSF 32tpi M6 25.4tpi, 1/4"BSF 26tpi, M8 20.3tpi, 5/16"BSF 22tpi).

Originally Posted By: Stuart
a 1/4"-dia. stud that screws into an alloy component and takes a nut on the other end - both ends will be 26tpi but which end is BSF and which is Cycle?

Originally Posted By: machico
which is which.

Originally Posted By: Stuart
the fun starts

Originally Posted By: machico
are there any studs like that for Triumph?

I can't remember where but I think I must have come across it/them, or I wouldn't have thought of the problem?

Originally Posted By: Stuart
BSB - British Standard Brass - thread.

Originally Posted By: machico
It's so complicated!!

Not really. I didn't mean to confuse you; afaik, neither Triumph nor BSA, not any of their suppliers used it. However, sometimes it's difficult to get the correct Cycle-thread tap or die and, especially if you want to just clean up a thread, sometimes knowing about BSB can sort out the problem quickly. wink

Hth.

Regards,

#374831 - 05/23/11 5:52 pm Re: BSF and BSC [Re: machico]  
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Machico, 1/4BSF and 1/4 BSC both have 26 turns per inch. But the thread angle of BSF Has 55 deg, while BSC is 60 deg, the difference between te two is difficult to see with the naked eye. I advise to buy a thread gauge to determine what thread you are dealing with, but even with a thread gauge the difference between 1/4 bsf and 1/4 bsc will not be easy to spot.

Anyway, with the aid of thread gauges, a caliper and a screwthread tables it is usually fairly simple to determine what thread type you are dealing with.

Concerning BSC thread, it is not generally known that a type of BSC thread exists with 20tpi rather than 26tpi, this is used for the rocker spindles, and brake cams on the BSA Goldstar for example.
Confusing? maybe, but with the aid of the above mentioned tools it is certainly no rocket science to find out what thread you are dealing with on your British bikes.


Peter.
1974 Commando 850
1972 Trident T150T
1961 Goldie DBD34
1969 Benelli 250 sport special
#374854 - 05/23/11 8:23 pm Re: BSF and BSC [Re: machico]  
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All the pre units used coarse thread into alloy. That fine thread was a unit thing....
I've never had a case screw back out. If anything, they get tighter. Oh, and I don't use cap screws either as they are way too easy to over-tighten.
There are five 22tpi oddball fasteners on a pre unit. Four handlebar bolts and the one case bolt just below the cylinder in the back. Must be Whitworth or something else instead of CEI.
Bill


Bikes
1974 Commando
1985 Honda Nighthawk 650
1957 Thunderbird/T110 "Flying Tiger"
Antique Fans: Loads of Emersons (Two six wingers) plus gyros and orbiters.
#374936 - 05/24/11 6:17 am Re: BSF and BSC [Re: Stuart]  
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Hi Stuart,

I have been kinda confusing but I noticed that BSC isn't used into alloy for pre unit. As you said, they used coarser thread which is BSW into alloy. when I get confused regarding BSF 1/4 26tpi and BSC 1/4-26tpi, I will follow the line which is "BSF into iron or steel". It is kida easy rule but I still don't get used to the british thread.. frown

Thanks,
Machico

#374938 - 05/24/11 6:51 am Re: BSF and BSC [Re: Peter R]  
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Hi Peter,

I have a thread gauge and the thread table but as you said, it is difficult for me to determine which pattern for the 1/4-26tpi is used by thread gauge and naked eye. When I wanted to clean the 1/4-26tpi thread with tap, I just couldn't figure out which tap I should use into the thread. Only 1/4-26tpi makes me confused because they have same size and same tpi. frown

Originally Posted By: Peter R

Concerning BSC thread, it is not generally known that a type of BSC thread exists with 20tpi rather than 26tpi, this is used for the rocker spindles, and brake cams on the BSA Goldstar for example.


Surely BSC 9/16-20tpi is used to gearbox adjuster for rigid pre unit too.

Anyway, as you said, it is easy to determine the thread type by using the gauge and the table but I still have to be used to the british thread. frown

Thanks,
Machico

#374944 - 05/24/11 7:24 am Re: BSF and BSC [Re: HawaiianTiger]  
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Originally Posted By: HawaiianTiger
All the pre units used coarse thread into alloy. That fine thread was a unit thing....

Yes, I noticed that BSW is used into alloy.

Originally Posted By: HawaiianTiger

I've never had a case screw back out. If anything, they get tighter. Oh, and I don't use cap screws either as they are way too easy to over-tighten.


I don't use cap screws either. I have broke up the thread hole before. eek

Originally Posted By: HawaiianTiger

There are five 22tpi oddball fasteners on a pre unit. Four handlebar bolts and the one case bolt just below the cylinder in the back. Must be Whitworth or something else instead of CEI.


Really? Four Handlebar bolts are BSF5/16-22tpi but the bolt just below the cylinder in the back is BSW5/16-18tpi. Mmmm.. wait. Not BSC but BSF is used for handlebar bolt?? confused

Anyway, it seems that small amount of BSF is used for pre unit.

Thanks,
Machico

#374964 - 05/24/11 11:18 am Re: BSF and BSC [Re: HawaiianTiger]  
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Originally Posted By: HawaiianTiger
All the pre units used coarse thread into alloy. l


Not quite all.

The short alternator Thunderbird primary case on my Triton has fine threaded screws holding the cover on.


Amateur Loctite enthusiast.
#374983 - 05/24/11 1:25 pm Re: BSF and BSC [Re: Stuart]  
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I found the 1/4 stud 26tpi both side. E3956. I'm not sure where to use it though. Maybe studs for AMAL?

Thanks,
Machico

#375026 - 05/24/11 5:02 pm Re: BSF and BSC [Re: machico]  
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Hi Machico,

Originally Posted By: machico
I found the 1/4 stud 26tpi both side.

That reminds me. Not strictly relevant to you but, on pre'69 (when they changed to Unified threads) single-carb. unit twins, the manifold is mounted to the head with four 1/4" studs. The head's alloy, so BSF; the other end of each stud takes a nut, so Cycle. There are probably others grin

Originally Posted By: HawaiianTiger
All the pre units used coarse thread into alloy.

Originally Posted By: triton thrasher
Not quite all.

Originally Posted By: Stuart
you can make an educated guess


Originally Posted By: machico
When I wanted to clean the 1/4-26tpi thread with tap, I just couldn't figure out which tap I should use into the thread.

Not helped by even the correct tap or die will almost always remove a small amount of metal from the thread. frown

If you're unsure whether to use a Cycle or BSF tap/die on a 1/4"-26 thread, if you think about it, start with Cycle. Because, with a 60-degree included angle on each thread peak or trough, from the same nominal outside diameter, the Cycle thread is slightly shallower than the 55-degree i.a. BSF thread.

Then, only if the cleaned thread still doesn't work, cut it a little deeper with the BSF tap or die.

Originally Posted By: machico
I will follow the line which is "BSF into iron or steel".

Originally Posted By: Stuart
BSF threads into aluminium alloy
Cycle threads into/on iron and steel

grin

Originally Posted By: Peter R
Concerning BSC thread, it is not generally known that a type of BSC thread exists with 20tpi rather than 26tpi,

Afaik:-

. 20tpi Cycle applies only to diameters 7/16" and larger;

. Triumph used them extensively.

Originally Posted By: Peter R
1/4BSF and 1/4 BSC

Originally Posted By: Stuart
BSF has a 55-degree included angle in the triangle formed by each thread peak or trough; otoh, as [Machico] said, Cycle has a 60-degree included angle. Nevertheless, in general, it's almost impossible on decades-old parts.

Always worth reading the whole thread before posting, so you don't post duplicate information. wink

Hth.

Regards,

#375071 - 05/24/11 9:01 pm Re: BSF and BSC [Re: Stuart]  
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Originally Posted By: Stuart
Hi Machico,
If you're unsure whether to use a Cycle or BSF tap/die on a 1/4"-26 thread, if you think about it, start with Cycle. Because, with a 60-degree included angle on each thread peak or trough, from the same nominal outside diameter, the Cycle thread is slightly shallower than the 55-degree i.a. BSF thread.

Then, only if the cleaned thread still doesn't work, cut it a little deeper with the BSF tap or die.


NOT SO with a tapped hole.Use a 26 tpi BSF or Brass tap first.Smaller nose radius and 55 degree angle takes out less metal.
A BSC die will take less metal off a bolt or stud.

#375306 - 05/25/11 9:55 pm Re: BSF and BSC [Re: Stuart]  
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Originally Posted By: Stuart

Originally Posted By: machico
I will follow the line which is "BSF into iron or steel".

Originally Posted By: Stuart
BSF threads into aluminium alloy
Cycle threads into/on iron and steel

grin



Oh shocked
Thanks for pointing out. I use BSF, BSC, BSW, Japanese and English. I got so mixed up crazy

Thanks,
Machico

#375314 - 05/25/11 10:21 pm Re: BSF and BSC [Re: Pete R - R.I.P.]  
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Originally Posted By: Pete R
Originally Posted By: Stuart
Hi Machico,
If you're unsure whether to use a Cycle or BSF tap/die on a 1/4"-26 thread, if you think about it, start with Cycle. Because, with a 60-degree included angle on each thread peak or trough, from the same nominal outside diameter, the Cycle thread is slightly shallower than the 55-degree i.a. BSF thread.

Then, only if the cleaned thread still doesn't work, cut it a little deeper with the BSF tap or die.


NOT SO with a tapped hole.Use a 26 tpi BSF or Brass tap first.Smaller nose radius and 55 degree angle takes out less metal.
A BSC die will take less metal off a bolt or stud.


mmmmm, I have never seen the drawing of the both type of threads so I'm not sure exact dimension but I think the BSF thread is shallower than BSC thread to me if I think of it simply. They have same diameter and same tpi. So as Pete R said, it seems that the BSF have a smaller nose radius than BSC. BSF 26 tpi tap first for the holes and BSC die first for the bolts and studs sound better to me. smile

Thanks,
Machico

Last edited by machico; 05/25/11 10:28 pm.
#375324 - 05/25/11 10:47 pm Re: BSF and BSC [Re: machico]  
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Hi Machico,

Originally Posted By: machico
I have never seen the drawing of the both type of threads

BSF, Cycle

Originally Posted By: machico
I think the BSF thread is shallower than BSC thread

As you can see from the table under each drawing, for the same nominal o.d., Cycle thread core diameters (i.e. measured from the bottoms of two opposite threads) are greater than BSF thread core diameters. So the Cycle thread must be shallower than the BSF thread.

Originally Posted By: machico
They have same diameter and same tpi.

But the included angle at the nominal peak or trough of each thread is different. Or, as I say, just compare the core diameters for each o.d. wink

Hth.

Regards,

#375337 - 05/26/11 12:09 am Re: BSF and BSC [Re: Stuart]  
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Originally Posted By: Stuart
Hi Machico,

Originally Posted By: machico
I have never seen the drawing of the both type of threads

BSF, Cycle

Originally Posted By: machico
I think the BSF thread is shallower than BSC thread

As you can see from the table under each drawing, for the same nominal o.d., Cycle thread core diameters (i.e. measured from the bottoms of two opposite threads) are greater than BSF thread core diameters. So the Cycle thread must be shallower than the BSF thread.

Originally Posted By: machico
They have same diameter and same tpi.

But the included angle at the nominal peak or trough of each thread is different. Or, as I say, just compare the core diameters for each o.d. wink



First, I misunderstood the word "shallow". I thought it means narrow or something but it is different. Sorry.

Thanks. I saw the both drawings. Now I understand what you are saying. Surely BSC thread is shallower than BSF thread when I compare the core diameters. That's why the bigger size of tapping drill is used for BSC. According to the table and the drawing, when I'm unsure whether to use BSF 1/4-26 tap or BSC 1/4-26 tap, it's better to use the BSF tap first instead of BSC not to make the core diameter of the hole bigger. When I clean the studs and bolts, it's better to use BSC die first. smile

Thanks,
Machico

#375393 - 05/26/11 11:20 am Re: BSF and BSC [Re: machico]  
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I just refreshed my memory with a quick peek at my copy of "Machinery's Screw Thread Book; 20th Edition 1969"!

BSW and BSF conform to the Whitworth threadform which has a 55 degree thread angle. British Standard Cycle thread has a 60 degree thread angle. BSF and BSCy only coincide at 26 tpi 1/4" major diameter. You would be very pressed to notice the difference if using a tap to chase out a thread.

Regarding the usage of BSF; my '60 T120 only has one BSF thread holding the handlebar clamps (Steel bolts into the forged triple-T). This is 5/8" 22 tpi. (presumably this thread pitch was chosen as a compromise between strength and vibration performance) All other threads were BSW (almost always into castings), BSCy 26 for fasteners (although there seems to be an unofficial optional 20 tpi for 1/2" and above) and BA for electrical and instruments. After 1962, (I am not sure of my ground which models and when), there was a progressive adoption of unified threads but with the retention for quite a long time of BSW in castings (a mish-mash if you want).
It's almost like a history lesson which started in the Industrial Revolution!
FWIW


mike
Member #: 147
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1999 H*%^a VFR 800 FI
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#375419 - 05/26/11 2:15 pm Re: BSF and BSC [Re: t120mike]  
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Hi Mike,

Originally Posted By: t120mike
After 1962, (I am not sure of my ground which models and when), there was a progressive adoption of unified threads

Ime, you don't see BSA itself (the parent company rather than the marque) adopting Unified threadforms 'til 1968. In 1965, the British government announced the Britain was going metric and the changeover would take ten years. The British automotive industry's (when we had one) answer was to adopt Unified threadforms, which is mainly why BSA did.

Originally Posted By: t120mike
with the retention for quite a long time of BSW in castings

BSA's policy seems to have been that threads were only changed if a component was redesigned. Obviously, that wasn't always possible - if the changed component affected those around it, the threads on those might have to be changed to match, even if the components themselves weren't otherwise changed. Otoh, for example, in the 500 and 650 cylinder blocks, the threads for the head bolts and studs remained Cycle - I believe the bigger block changed to Unified when the capacity was increased to 750(?) - but the 500 block never did.

Originally Posted By: t120mike
BSCy 26 for fasteners (although there seems to be an unofficial optional 20 tpi for 1/2" and above)

In fact, 7/16" and larger-diameter Cycle threads can be 26tpi or 20tpi; Triumph used 20tpi where it was available, I'm only not sure what the standard was for 7/16" specifically.

Hth.

Regards,

#375423 - 05/26/11 2:45 pm Re: BSF and BSC [Re: machico]  
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Confirm that the 650 head bolts and studs remained as Cycle thread right to the end of the 650 Bonneville (certainly on my 1974 T120RV---one of the last 650 Bonnies).
You are right IME that they changed to Unified threads on the 750 Head bolts and studs.
In terms of the 1/4" BSF vs. BSCY situation IME after 40/50 years it doesnt much matter which you use--- the threads are pretty much buggered about by now.
I have just finished stripping a 1965 T100SR and on the fringe parts (the parts that DPO could get to easily) I found BSF, BSCy, UNC, UNF and metric threads and fasteners!
HTH

Last edited by Tridentman; 05/26/11 3:02 pm.
#375447 - 05/26/11 4:54 pm Re: BSF and BSC [Re: Tridentman]  
Joined: Oct 2009
Posts: 226
machico Offline
BritBike Forum member
machico  Offline
BritBike Forum member

Joined: Oct 2009
Posts: 226
JAPAN
Hi Tridentman,

Originally Posted By: Tridentman
Confirm that the 650 head bolts and studs remained as Cycle thread right to the end of the 650 Bonneville (certainly on my 1974 T120RV---one of the last 650 Bonnies).


This is interesting. I have 1968 TR6C and am interested in Unit triumph too. Thanks for the informative info.


Originally Posted By: Tridentman

In terms of the 1/4" BSF vs. BSCY situation IME after 40/50 years it doesnt much matter which you use--- the threads are pretty much buggered about by now.


I think so too. I may not have to be so nervous about it because the taps or dies may be made with worn out equipment and the reproduction bolts and nuts may be made with worn out tap, dies or lathe after all. As you said, the threads may be buggered about by now. But what if the parts I want to clean is NOS? confused

However, I'm new to Triumph and want to use right tool as much as I can to learn the British threads and tools. smile


Originally Posted By: Tridentman

I have just finished stripping a 1965 T100SR and on the fringe parts (the parts that DPO could get to easily) I found BSF, BSCy, UNC, UNF and metric threads and fasteners!
HTH

shocked shocked shocked!! Crazy! too many kind of threads! crazy

Thanks,
Machico

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