Oil pump drive and lock nut spanner size

[Sakura]

The only spanner or socket I have found that will fit the oil pump drive and locknut is a 25/32" AF. I know of no other metric or Whit size that will fit. Some older BSAs also have an odd 19/32"  hex size in various places. Why?
 In the case of the oil pump dive the thread is L/H so I could guess it's to make you think twice, but the nut is marked LH and it's noted in workshop info.
Does anyone have the definitive answer or is to remain forever a mystery?

[1949BSA]

I took off the nut + oil pump drive from an 1949 A7 Long stroke yesterday.
WW spanner do not fit save, but 20mm metric.
I do not know, if there was a change to the shortstoke engine.

Michael

[limeyrob]

I did mine recently and was annoyed to find it was not a Whitworth size, but I suspect since it made from hex stock is the size of the bar and perhaps they wanted an odd size on the assembly line to make sure it was done up left handed?

[Sakura]

The only sizes of hex stock that I'm aware of (and I worked in Industry and manufacturing all my working life) are standard sizes, Whit, AF and Metric. The size is definitely 25/32", 20mm is too lose. 19.5 metric fits, if you file an open ended spanner, but that's non standard. Still a mystery.

[Rex]

This has been mentioned before. BSA were a huge industrial conglomerate manufacturing many different products, and presumably one division ordered incorrectly (or too much) hex stock of a particular odd size, and the bean counters made sure it was used up rather than dumped.
Better it was used on motor bikes (where the customer is unlikely to complain) than rifles, cannons, field guns, armoured cars etc where bastard sizes would have potentially life-threatening results.

[Sakura]

This has been mentioned before. BSA were a huge industrial conglomerate manufacturing many different products, and presumably one division ordered incorrectly (or too much) hex stock of a particular odd size, and the bean counters made sure it was used up rather than dumped.
Better it was used on motor bikes (where the customer is unlikely to complain) than rifles, cannons, field guns, armoured cars etc where bastard sizes would have potentially life-threatening results.

I doubt that was the case as the hex on the oil pump drive is the same size and was machined, not bar stock. Still a mystery.

[trevinoz]

That is not the only place that 25/32 AF was used.

[groily]

A less common (but nonetheless standard) AF size which is available in o/end (Ministry of Defence surplus stock, dirt cheap), combination or cranked ring with various sizes at t'other end (Stahlwille, Facom and probably others at not insane cost), also as a 12 pt socket from Teng. Not sure if 'in a set' or 'individual purchase' for that.
Also at least one cranked ring on e-bay at 9 Aus dollars when I looked.
My own (and only) 25/32" is a well-made slim TruFit cranked ring (US made) acquired for next to nothing at a flea market 30 years ago, and has served on several occasions. Worth having, I think.
Some vendors pass off 20mm as being 'the same'; it'll probably 'do' but it's a fraction oversize as mentioned. A better feeling to have the correct item though, especially on things that matter or get visited regularly.

[limeyrob]

I don't know which is more bizarre: that the BSA crank nut is 25/32" AF or that Stahlwille, a German company, make and sell a 25/32" spanner:
https://www.primetools.co.uk/product/stahlwille-13a-combination-spanner-2532-x-235mm-long/
Is there someone in Germany wondering why they make a spanner that sells one a decade or have we missed the huge global demand for 25/32" AF spanners. It is odd.

[groily]

. . . . or that Stahlwille, a German company, make and sell a 25/32" spanner:
https://www.primetools.co.uk/product/stahlwille-13a-combination-spanner-2532-x-235mm-long/
Is there someone in Germany wondering why they make a spanner that sells one a decade or have we missed the huge global demand for 25/32" AF spanners. It is odd.

Demand for that one is probably pretty darn small Rob, has to be - but Germany makes / made excellent Brit-sized imperial spanners. A lot of my BSF/BSW favourites are branded ELORA or GEDORE and made there. Seriously high quality, look as new after a heck of a lot of daily use. Could ask the same Q of Facom I suppose - not much need on French built machinery either.

Maybe the accountants have caught up now though, haven't had to buy any for a goodly while!

[limeyrob]

We don't need to rely on Johnny foreigner: Britool 2J7881

[limeyrob]

OK this is beyond bizarre. I just did an e-bay search for 25/32 spanner and there are over 400 (yes 400!) on e-bay.  So what was the huge demand for 25/32 spanners?  Or are they the spanner equivalent of "pet rocks" - everyone wanted one for a week.

[JulianS]

I use the spanner BSA made - part 15 832 - fits perfectly and ground flat so it engages the full depth of the thin lock nut and does not slip off and round the edges. Designed to hammertite in the days when no torque was given.

If you use a socket consider grinding it flat so it fits the full depth of the nut.