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B175 carb to cylinder stud thread size.
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nickjaxe
Runcorn Cheshire UK
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June 13, 2018 - 4:20 pm
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B175 carb to cylinder fixing studs...Thread has gone on one of mine.

Not got around to trying to remove it yet...but I wonder...does anybody know if the threaded end going into the barrel is metric....on mine the end the carb fits on is metric course thread which did surprise me.

If its metric both ends I will have some.

And doe they usually rust it the cylinder end...I could see the being a «censored» to get out...any tips before I start.

Nick.

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sunny
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June 13, 2018 - 6:27 pm
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its  not  serpose   to  be  the  same   both  end   as  it  can come  undone   too  ezy

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Peterg
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June 13, 2018 - 7:38 pm
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5/16 unf/ unc 1 1/4"

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Blue Heeler
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June 14, 2018 - 8:37 am
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If they`re metric then someone has already fitted replacements.Hopefully they haven`t boogered the threads in the cylinder,because the original UNC is a coarser thread than metric.If they`ve been loctited in then they may take a bit of getting out.

If there`s enough thread to get two nuts on and lock them against each other try that method first,using the inner one to undo the stud with.If not,then a small knurled stud extractor should get it going for you....or a good set of moles.

They usually come out really easily in my experience,so much so that they come out when you don`t want them to....ie when trying to remove the UNF nuts if they`ve been on for some time and corroded,when you`re trying to remove the carb.

Easier enough to make your own up.....with your recently purchased bargain set of dies and a decent piece of bar :)...oh hang on they were Whitworth werent they?Anyway,new studs shouldn`t be that expensive to buy.

Blue

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nickjaxe
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June 14, 2018 - 9:10 am
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Hi Blue...managed to get hold of Rex yesterday so some on the way...no idea if they will fit...just hope a PO has not «censored» about with it.

Good tips re getting the old ones out.

Let you know how I go on.

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nickjaxe
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June 15, 2018 - 9:17 pm
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Hi blue...came out ok with your idea 2 nuts locked together.

Could do with finding out what the thread size is going into the barrel....I now dont think the carb end on my studs where metric...as the metric nut that where on mine when a good fit on the new studs carb end...the barrel end is a coarser thread...its that one I want to know the thread size and pitch.

Nick.

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Piquet
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June 16, 2018 - 2:05 am
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Most B175 threads are detailed in the Parts Manual.

I'm not a complete idiot ............................................ some parts are missing.

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AWJDThumper
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June 16, 2018 - 7:00 am
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As said, the parts book gives the stud as 5/16 UNC going into the cylinder and UNF for the nuts that secure the carb. The length given is 1 3/8". The easiest way to confirm if the cylinder thread is ok, is to get hold of a 5/16 UNC bolt (or stud) and see if it screws in ok. I think it's highly unlikely that the cylinder thread has been changed as it takes some effort to damage cast iron unlike the aluminium used on other BSA top ends.

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Blue Heeler
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June 16, 2018 - 9:06 am
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Nick, I`m sure Rex`s studs`ll fit ok... it`s the original fine threads that get mullered because some people use random nuts to bolt their carbs up.Because there`s a force fit onto the fine thread it chews it up,but often not before it`s turned the shoulder of the stud into the threads of the barrel....but that usually only makes them a little harder to remove,and creates metal spread to the carb flange face,which is easily filed/radiused down for a flat finish.Steel cylinder studs  into the alloy of crankcases are particularly prone to causing this.

Use the same double-nuts locked together method to fit the new studs.Cast iron has its own inbuilt lubrication properties,the old studs will have cleaned the barrel threads nicely as you removed them I expect.Hopefully you`ve got two nice shiny new nuts,plain washers and springs too.The plains protect the soft alloy of the carb being spread onto the stud`s fine threads by the nasty springs 🙂

Job`s a gudun.

Blue

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nickjaxe
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June 16, 2018 - 9:47 am
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I now realised just how little I know about nut/bolt threads....before I bought a British bike all I had to think about was AF or metric systems.

I wonder is UNF and UNC a form of the BSW thread type.

I think I need to get myself a thread gauge.

Will one of these cover all threads we need to id.

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The thread on the end of the stud that screws into the barrel was perfect on my old studs...the carb end on both was chewed...had the nut on it that where on the bike when I bought it.

Thanks for your help again guys.

Nick.

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AWJDThumper
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June 16, 2018 - 10:08 am
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Unified threads were introduced during WW2 to ensure compatibility of the equipment used by the allies. Prior to this, the British used British Standard threads and the US used National threads (NF and NC). BSA started to adopt the unified (UNF and UNC) threads in the late 1960's and, early, on you could find both BSW/BSF and UNF/UNC on the same bike until the old stocks were used up. Interestingly, 5/16 UNC and BSW are both 20 TPI and it's only the thread angle that is different (60 deg vs 55 deg). At a push, you could screw a 5/16 BSW stud into the B175 cylinder head, although I wouldn't recommend it.

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mike p5xbx
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June 16, 2018 - 4:14 pm
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nickjaxe said
I now realised just how little I know about nut/bolt threads....
Nick.  

get a Zeus reference book or download a copy to go with the thread gauge
and a digital vernier gauge if you have not already got one
3 of the most necessary things to own with old Brit bikes

D? - D10- D14 Bantams 350 AJS -500 Triumph http://bsanotru.....lfire.com/

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nickjaxe
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June 16, 2018 - 5:58 pm
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Good tip Mike...I have a vernier...will have a look for the Zeus tables.

Mike will this Thread gauge be suitable for the fastenings on our bikes.

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Nick.

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mike p5xbx
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June 16, 2018 - 11:32 pm
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yes looks ok
did you know there are Seven different thread types you are likely to find used
on old brit bikes and thats before you include the odd metric nut/bolt tapped hole used by a former owner

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nickjaxe
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June 17, 2018 - 10:11 am
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Wow 7...I didn't realise no.

Just to clarify...UNF and UNC...are the a separate std to BSF....BSW.

All a bit of a mine field.

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cocorico
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June 17, 2018 - 11:31 am
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As Mike has already said - find a set of Zeus Table, or search online for thread identification charts, there are plenty there.

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mike p5xbx
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June 17, 2018 - 5:45 pm
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nickjaxe said
Wow 7...I didn't realise no.
Just to clarify...UNF and UNC...are the a separate std to BSF....BSW.
All a bit of a mine field.  

Unf and Unc are American SAE standard no idea why we added another two thread types not as if we did not have enough already
I have read that the Unified Thread Series was agreed on by the United States, Great
Britain and Canada in 1949 to obtain interchangeability ! (that not how you spell confusion is it )
UNC and Whitworth are very similar and very easy to get mixed up
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makes good bedtime reading

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Peterg
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June 17, 2018 - 8:57 pm
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In my experience metric and af nut sizes are almost interchangeable in terms of spanner size.

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nickjaxe
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June 17, 2018 - 9:42 pm
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Well I have found this thread...Mmmm did I really say that...anyway found it educational.

Over the years I have always collected suplus nuts bolts washers ect...always coming in usfull for all kinds of jobs...never been stuck for a replacement nut or bolt...but never know a great lot about the obscure types of thread.

So I have ordered my self the thread pitch gauge...in the past I just kept trying different nuts/bolts till I found on that fitted but the old imperial have always given the most trouble...my old Landrover has its share of old imperial sizes and type.

But I have a better understanding thanks to you guys.

So many thanks for pointing me in the right direction.

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Blue Heeler
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June 17, 2018 - 11:36 pm
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Peterg said
In my experience metric and af nut sizes are almost interchangeable in terms of spanner size.  

Yeah,comes in very handy with finding a spanner/socket to fit rusted/worn nuts/bolt heads,eg 1/2AF fits worn 13mm or 1/4W nuts....or a worn 1/2AF spanner/socket  fits 13mm and 1/4W nuts snugly.

11mm & 7/16AF,19mm & 3/4AF...etc,etc

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