Author Topic: Thread form on pattern parts  (Read 497 times)

Online Kickaha

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Thread form on pattern parts
« on: 12.09. 2021 07:53 »
Recently I bought an A10 single seat and thought I would buy new fasteners for it, so without checking the actual seat I got the 5/16 26 tpi bolt from a place in Oz so I could leave the other fasteners and bracket with the dual seat, while unsuccessfully trying to screw them together I worked out the threads in the new seat are 8mm x 1.25 which seems an odd choice for a 60+ year old machine

This came from Feked and was labelled Wassell underneath, while I have no complaint about the overall quality of the item and the service from Feked was good, it does seem odd that someone would go to the trouble of producing an item like that and not using the correct thread form for the era

I'll probably just use the 8mm bolts as that's the easiest way out but it is an extra spanner/socket to carry

The slots in the front seat bracket are also slightly undersized and wont fit over the bar at the front to locate so a few minutes with a file will be required there as well

In contrast on my Indian made Fuel tank the threads are all the same as my original
1956 BSA Gold Flash
New Zealand

Online Rex

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Re: Thread form on pattern parts
« Reply #1 on: 12.09. 2021 08:32 »
The Indians seem to use what they have available. You could always knock up an Imperial headed bolt with metric threads though and save carrying additional spanners.

Offline Swarfcut

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Re: Thread form on pattern parts
« Reply #2 on: 12.09. 2021 08:45 »
 KK.   Par for the course these days. Metric Taps, Dies and Industrial fixings are cheap, so that's what you get.

     A  seat  I bought in the 1970's had metric captive nuts. Back then UNF, UNC and BSF were the threads in your nut and bolt box, and buying metric nuts and bolts was the new order. So that came as a surprise, I thought I was getting a genuine BSA seat with cycle thread fixings. No, it was an unbranded pattern part along with the others entering the distribution chain as the established major  suppliers collapsed and you did not always get what you were expecting. The dealers charged the full BSA price, plus the newly introduced VAT (Sales Tax) whether they were registered for VAT or not..... No change there, then.

 There were also nuts and bolts with metric threads and flats to fit your old  AF Spanners. A sort of  halfway house as the new world of metrication swept away the established thread forms. The auto industry used these, allowing modern threads to be used in production, but permitting the continued use of your old socket sets and spanners.  I think we called them ISO Bolts. Talk about confusing!!

 Swarfy.

Online Kickaha

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Re: Thread form on pattern parts
« Reply #3 on: 12.09. 2021 20:28 »
. You could always knock up an Imperial headed bolt with metric threads though and save carrying additional spanners.

Good idea, a job that is above my skill level but I know someone who can
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Online Colsbeeza

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Re: Thread form on pattern parts
« Reply #4 on: 13.09. 2021 01:47 »
I have usually had difficulty fitting the Rocker cap elongated nuts which I had assumed were 1/4" Cycle Thread. I moved any tight nuts to another stud if it went down easier.  I purchased these nuts a few years ago.
Any way I got the Sh--ts the other day so thought I'd have a closer look. I ran a 1/4" die nut down one stud to check and it fitted quite well, no metal removed. So definitely 1/4" BSCy. So I thinks the nuts are at fault, so ran a 1/4" BSCy tap through the nuts. All 8 went through with considerable firmness and a fair bit of swarf. I didn't check the thread before running the tap through.  I can't remember where I got them, but may have been 1/4" BSF which most suppliers are supplying as a substitute for 1/4" BSCy.
Problem fixed.
Col
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Online KiwiGF

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Re: Thread form on pattern parts
« Reply #5 on: 13.09. 2021 06:37 »
I have usually had difficulty fitting the Rocker cap elongated nuts which I had assumed were 1/4" Cycle Thread. I moved any tight nuts to another stud if it went down easier.  I purchased these nuts a few years ago.
Any way I got the Sh--ts the other day so thought I'd have a closer look. I ran a 1/4" die nut down one stud to check and it fitted quite well, no metal removed. So definitely 1/4" BSCy. So I thinks the nuts are at fault, so ran a 1/4" BSCy tap through the nuts. All 8 went through with considerable firmness and a fair bit of swarf. I didn't check the thread before running the tap through.  I can't remember where I got them, but may have been 1/4" BSF which most suppliers are supplying as a substitute for 1/4" BSCy.
Problem fixed.
Col

Possibly even worse is that metric almost fits 1/4”, it”s not uncommon to find a 6mm x 1mm bolt or screw fitted in a 1/4” ID. cycle thread hole in old brit bikes, but it would be a loose fit (my B44 has 1/4” cycle thread in castings.....and a PO had fitted metric allen head screws 😣 which I am gradually replacing with difficult to find pozidrive screws)

A 6mm ID nut may also get forced onto a 1/4” OD stud, but it would be tight, the nut may have an 11mm AF hex so a 7/16” spanner would fit it as well 🤨

metric (1 mm pitch)  is 25.4 so not far off 26 tpi cycle
1/4” is 6.35mm (so slightly larger than 6mm)
New Zealand

1956 A10 Golden Flash  (1st finished project)
1949 B31 rigid “400cc”  (2nd finished project)
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Online berger

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Re: Thread form on pattern parts
« Reply #6 on: 13.09. 2021 12:08 »
KiwiGF i had to drill out a 1/4 wheel adjuster bolt on a notrun swinging arm that had been snapped off flush. i hadn't got quite far enough down and decided to go in again and the drill broke leaving two small pieces in the bottom*eek* i then had to take the hole out a bit bigger and got the bits out and  tapped it 7mm. the 7mm bolt i used had the same AF size as you mentioned 7/16 so i thought good result i don't have to use different sized spanners on each side *yeah*