Author Topic: 7/8 UNF thread?  (Read 643 times)

Offline Juddy

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7/8 UNF thread?
« on: 11.02. 2017 05:39 »
Hi kids.

Well less than a day after getting my bsa a10 back from the mechanics. I find that the buggers have left a nut of the through bolt securing part of the gearbox to the frame (Right at the base of the frame).

So my questions are....
1) What thread are we dealing with here? (The chap at the local fastener place said it was 7/8 UNF but i've got some doubts)

2) Does anyone here have any of the nuts in question that may be acquired?

3) Where am I able to get a copy of a workshop/parts manual?

Thanks in advance chasps!!!!

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Re: 7/8 UNF thread?
« Reply #1 on: 11.02. 2017 06:26 »
G'day Juddy.
My 1st thought was it would have to be 7/16 cycle thread. Then I looked up the part # for the stud 42-4077 and found it to be 7/16-20 UNF 4 1/2 long. *doubt*
If you have a part number for a fastener a good site to check http://stainlessbits.com/link12.html
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Offline Tomcat

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Re: 7/8 UNF thread?
« Reply #2 on: 11.02. 2017 06:46 »
Gday Juddy. Are we talking plunger or swingarm frame? IIRC Swingarm are 3/8" and 7/16"and 26 tpi, unless PO has reamed out a mess. I measure all fasteners with verniers and check TPI with a thread gauge as it saves time. Have a look at Draganfly website to identify the part, sometimes the sizes are with the price. https://www.draganfly.co.uk/index.php/bsa/bsa/a710--b3133--c101112--m202133/category/895-pre-unit-a-group  FYI Classic Fasteners http://www.classicfasteners.com.au/ is my 1st choice for BSCY fasteners in AU
Cheers TC
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Online trevinoz

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Re: 7/8 UNF thread?
« Reply #3 on: 11.02. 2017 20:55 »
The nut is 7/16" x 20 tpi cycle but the U.N.F. nut will fit.
Note that the original nuts have a hexagon of 25/32" A.F.  Just another BSA anomaly.

Offline Juddy

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Re: 7/8 UNF thread?
« Reply #4 on: 12.02. 2017 00:58 »
Hey lads

Thanks for your help so far....

It's a swingarm frame (58 I beleive) and this is the part descriptor that i've found, "Gearbox plate pivot stud to gearbox, lower". Looking at the thread on the part itself i think we're looking at 20TPI or somewhere in that range?

Offline Tomcat

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Re: 7/8 UNF thread?
« Reply #5 on: 12.02. 2017 08:26 »
The nut is 7/16" x 20 tpi cycle but the U.N.F. nut will fit.
Note that the original nuts have a hexagon of 25/32" A.F.  Just another BSA anomaly.


Thanks Trevor, now i know what that weird size (25/32") socket is for!
'48 A7 '59 SR '74 850 Commando TDM900

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Re: 7/8 UNF thread?
« Reply #6 on: 12.02. 2017 20:28 »
While we are at it, the locknut on the oil pump worm is also 25/32" A.F.

Offline Juddy

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Re: 7/8 UNF thread?
« Reply #7 on: 16.02. 2017 02:57 »
Hello again everyone.

Update time. Well after purchasing 2 x 7/16 BSCY thread nuts from http://www.classicfasteners.com.au/ as suggested by Tomcat (Cheers mate). I was very happy to receive the same the very next day, absolutely brilliant service and updates throughout the afternoon and next day as to the status of my package. I cannot recommend these people highly enough. Now to the fun part.....

I proceeded to apply the nuts to the thread (both sides) with no joy. Then I reapplied the old nut that i still had and it went on fine (both sides) but i did notice a little galling on the thread but that could be explained by over tightening, and was easily cleaned up with a fine jewellers file. I was struggling to find my thread gauge but calculated that it was indeed 20 TPI. I then decided to enlist my fathers help for checking purposes, and we both came up with the same results. So it was then decided to, just for curiositys sake to run a 7/16 NF 20 TPI die down the thread, and a tap for the existing nut. Sure enough as Tomcat suggested. The P.O. had done that, there was very miniscule amounts of swarf coming off the thread, this stuff was so fine you could hardy see it, human hair width is a good likeness. So I made the decision to do the same to tap the BSCY threads to the same to save re ordering. So now its in-situ and doing what it's meant to be doing.

Offline Juddy

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Re: 7/8 UNF thread?
« Reply #8 on: 16.02. 2017 03:01 »
P.S

That's little mate steve in the bottom pic helping out. Just a little but not so subtle hint of the next installment in another are of the forum.....

Offline kiwipom

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Re: 7/8 UNF thread?
« Reply #9 on: 16.02. 2017 03:20 »
hi guys, Oh No, I wonder if the bean counters would notice, lol, cheers
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