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Crankshaft rotor thread confusion #503796
08/29/13 9:47 am
08/29/13 9:47 am
Joined: May 2010
Posts: 190
UK
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berniej Offline OP
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UK
Hi all,

I need to replace the rotor nut on my Jan '62 A65. The nut shown in the parts book is 9/16 but mine is 5/8 and I thought measured at 20 TPI. However the 5/8 x 20 nut I've just bought doesn't fit.

Anyone know what it should be?

Thanks,
Bernie


'81 T140
'62 A65
'56 SQ4
'49 M21
'62 99 Dommie
S8 project
G80 project
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Re: Crankshaft rotor thread confusion [Re: berniej] #503807
08/29/13 11:58 am
08/29/13 11:58 am
Joined: Jun 2008
Posts: 550
Rotherham, UK
Ian Clifton Offline

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Ian Clifton  Offline

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Posts: 550
Rotherham, UK
Bernie.. In true BSA fashion they keep a part number the same(29-2023), but alter the thread!! Earlier engines have a 5/8" CEI (20 TPI?) thread nut, but from 1969 on the nut was a 5/8" UNF (18 TPI). Do you have thread gauges to measure the TPI? Maybe you have a later crank fitted (not sure whether compatible with earlier cases though) I'm sure someone will correct me if I'm wrong.. HTH Ian

Last edited by Ian aka Frank; 08/29/13 12:00 pm.

Just a few Beezers.. ☺

Re: Crankshaft rotor thread confusion [Re: berniej] #503809
08/29/13 12:17 pm
08/29/13 12:17 pm
Joined: May 2013
Posts: 4,681
Rotherham - S. Yorkshire
Allan Gill Online happy
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Allan Gill  Online Happy
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Rotherham - S. Yorkshire
A later crank is identifiable (when out of the cases) by a single sludge trap plug. Early motors have one each side.

http://www.classicmotorcycles.org.uk/technical/technical_thread_size_chart.htm

BSF would be 16tpi @ 9/16 and 14tpi @ 5/8

Cycle thread would be either 26 tpi or 20tpi for both these sizes (god bless the Germans for the metric system!)


beerchug
Re: Crankshaft rotor thread confusion [Re: berniej] #503812
08/29/13 12:37 pm
08/29/13 12:37 pm
Joined: Jun 2002
Posts: 9,469
Scotland
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Stuart Online content
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Stuart  Online Content
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Hi Bernie,

Originally Posted By: berniej
the 5/8 x 20 nut I've just bought doesn't fit.

There's another little wrinkle - the nuts are often covered in a hard brown preservative, that's thick enough to make the thread oversize and it apparently doesn't fit. cry The brown stuff's a bu66er to remove too, doesn't dissolve in degreaser - I usually run a tap down those nuts before attempting to fit them.

Hth.

Regards,

Re: Crankshaft rotor thread confusion [Re: berniej] #503823
08/29/13 2:58 pm
08/29/13 2:58 pm
Joined: May 2010
Posts: 190
UK
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berniej Offline OP
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berniej  Offline OP
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Joined: May 2010
Posts: 190
UK
Thanks all - it has the double ended sludge trap so I reckon it's the original crankshaft and the threads have been munged by a P.O. - looks like a punch mark to secure the rotor nut instead of a new washer.

I measured the pitch with a vernier and then ordered 3/8 x 20 die (to clean and recut damaged threads) and SS nut but they don't seem right.

I'll get a TPI thread guage and double check the crank thread.

Got to get this bike right by next summer 'cos we're planning to crash the Cheshires again on your summer camp!

Cheers,
Bernie


'81 T140
'62 A65
'56 SQ4
'49 M21
'62 99 Dommie
S8 project
G80 project
Re: Crankshaft rotor thread confusion [Re: berniej] #503918
08/30/13 10:02 am
08/30/13 10:02 am
Joined: Mar 2011
Posts: 833
derby england
wak Offline
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wak  Offline
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derby england
iv measured an early and late crank both are 5/8 x 20 which is 20tpi series cycle thread, taps are available on eBay uk


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Re: Crankshaft rotor thread confusion [Re: berniej] #503924
08/30/13 10:46 am
08/30/13 10:46 am
Joined: Mar 2005
Posts: 10,024
Boston, Massachusetts
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John Healy Online content
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John Healy  Online Content
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Boston, Massachusetts
Quote:
god bless the Germans for the metric system!


Wasn't it the French during Napoleon's era?

Quote:
god bless the Germans for the metric system!


If there is anyone to thank it is the good folks at the International Standards Organization (ISO). Before ISO was universally adopted around the globe nearly every country and/or manufacturer had their own version of what they facetiously referred to as "Metric". One could not take a screw out of a Bultaco and thread it into a Ossa. The screws from a Yamaha would not fit into a Kawasaki, and on it went.


Re: Crankshaft rotor thread confusion [Re: John Healy] #503950
08/30/13 1:21 pm
08/30/13 1:21 pm
Joined: Jun 2002
Posts: 9,469
Scotland
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Stuart Online content
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Stuart  Online Content
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Posts: 9,469
Scotland
Hi John,

Originally Posted By: John Healy
Quote:
god bless the Germans for the metric system!

Wasn't it the French during Napoleon's era?
If there is anyone to thank it is the good folks at the International Standards Organization (ISO).

'Twas indeed the French, but before Napoleon's time - he just spread it (along with driving on the right (wrong) side of the road) to every country he conquered, and then every one those countries colonised. frown

The metre was originally defined during the French Revolution. At one stage, the revolutionaries tried to decimalise everything - 10 hour days and 10-day weeks - the latter didn't go down well with les citoyens and was abandoned tout de suite (sorry smile ). In defining the metre, the revolutionary committee wanted a line between the North Pole and the Equator passing through Paris to measure 10,000,000 metres;unfortunately the mathematicians of the day screwed up and it measures 10,000,882 metres.

So the entire metric system is based on a mistake, and even the ISO couldn't fix that. Us Brits were right to have no truck with such barmy systems. cool

Hth.

Regards, grin

Re: Crankshaft rotor thread confusion [Re: berniej] #504036
08/31/13 4:12 am
08/31/13 4:12 am
Joined: May 2010
Posts: 190
UK
B
berniej Offline OP
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berniej  Offline OP
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Joined: May 2010
Posts: 190
UK
Hah - might have guessed it, my thread woes are all due to Johnny Foreigner....

Looking around various sources of thread form info I think what I need is the coarse CEI thread which is 20 TPI. The nut and die that I ordered are 5/8 x 20 but unspecified thread form. The only other thread form I can find that matches that is 'Admiralty Fine' which I hadn't heard of previously.

So, another search for nuts and die, specifiying CEI20 this time....

Cheers,
Bernie


'81 T140
'62 A65
'56 SQ4
'49 M21
'62 99 Dommie
S8 project
G80 project
Re: Crankshaft rotor thread confusion [Re: berniej] #504044
08/31/13 6:59 am
08/31/13 6:59 am
Joined: Jun 2002
Posts: 9,469
Scotland
S
Stuart Online content
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Stuart  Online Content
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Joined: Jun 2002
Posts: 9,469
Scotland
Hi Bernie,

Originally Posted By: berniej
my thread woes are all due to Johnny Foreigner....
The only other thread form I can find that matches that is 'Admiralty Fine'

Errr ... koff ... whisper it quietly but the "Admiralty" is the British Admiralty ... whistle We can't blame this on the EU ...

Originally Posted By: berniej
another search for nuts and die, specifiying CEI20 this time

Even if were Admiralty thread (which I very much doubt, the Admiralty stopped actually specifying them before God was an apprentice), they're the same form as Whitworth and BSF. The chances of that making a noticeable difference with 60-degree Cycle threads are infinitesimally small.

Hth.

Regards,


Moderated by  Allan Gill, Jon W. Whitley 


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