1938/39 and Big 7 back axle/shafts/nuts

[Dennis Nicholas]

1938/39 (heavy axle July 1938 onwards)
The half shafts are 14 thread per inch (TPI).  I measure them as being 3/4 inch diameter at thread.  3/4 inch BSF is given as 12 TPI but I notice in my Newnes Engineer's manual that 11/16 BSF is 14 TPI so can someone confirm they are actually 3/4 inches with an Austin special thread?.

Split pin for castellated nut.
I have found a pin that is a good, gentle tap fit into the hole and the head more or less fills the castle gap.  Using my micrometer this pin measures 0.132 inches (3.44mm).  But I only have one and the next nearest size is 0.1165 - 0.12 inches (2.93mm) which is a bit slack in the hole.  Bearing in mind that 1/8 inch is 0.124"  can I assume I am looking for 1/8 inch split pins to buy?

Possibly helpful interesting figures for getting hole and nut castellations lined up:-

14 TPI gives a pitch of 0.0714285 inch.
There are 6 slots in the nut therefore:-
Slot to slot = 1/6 X 0.0714285  = 0.0119047 inches

3/4 castle over hole = 3/24 X 0.0714285   = 0.0089285"  (9 thou) shim added to align hole/castle.
1/2 castle over hole = 1/12 X 0.0714285   = 0.0059523" (6 thou) shim added to align hole/castle
1/4 castle over hole = 1/24 X 0.0714285   = 0.0029761" (3 thou) shim added to align hole /castle

Note the above assumes the gap in the nut has gone passed the hole in the shaft so the nut needs to turn anticlockwise which will be achieved when adding the thickness shown.  You can use a thicker washer which is a multiple of the slot to slot size + the extra fraction of slot to slot size required.  This may be necessary if the nut is going too far onto the shaft so the hole is or is nearly beyond the castellations.

Also to note, nuts may be flange....these are the better ones to use.

(and lastly...don't forget to put the washer in after the oil seal and BEFORE the bearing!..........ah ok I should have put this first  )

Dennis

[Nigel Ricardo]

If you need a box spanner for the large hub nut (I think from memory its 1 16/17 )it is the same size as a Harley Davison Flywheel, I got mine online from a company called Fecked (yes,really )

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If you need a box spanner for the large hub nut (I think from memory its 1 16/17 )it is the same size as a Harley Davison Flywheel nut, I got mine online from a company called Fecked (yes,really )

[Jeff Taylor]

1938/39 (heavy axle July 1938 onwards)
The half shafts are 14 thread per inch (TPI).  I measure them as being 3/4 inch diameter at thread.  3/4 inch BSF is given as 12 TPI but I notice in my Newnes Engineer's manual that 11/16 BSF is 14 TPI so can someone confirm they are actually 3/4 inches with an Austin special thread?.

Split pin for castellated nut.
I have found a pin that is a good, gentle tap fit into the hole and the head more or less fills the castle gap.  Using my micrometer this pin measures 0.132 inches (3.44mm).  But I only have one and the next nearest size is 0.1165 - 0.12 inches (2.93mm) which is a bit slack in the hole.  Bearing in mind that 1/8 inch is 0.124"  can I assume I am looking for 1/8 inch split pins to buy?

Possibly helpful interesting figures for getting hole and nut castellations lined up:-

14 TPI gives a pitch of 0.0714285 inch.
There are 6 slots in the nut therefore:-
Slot to slot = 1/6 X 0.0714285  = 0.0119047 inches

3/4 castle over hole = 3/24 X 0.0714285   = 0.0089285"  (9 thou) shim added to align hole/castle.
1/2 castle over hole = 1/12 X 0.0714285   = 0.0059523" (6 thou) shim added to align hole/castle
1/4 castle over hole = 1/24 X 0.0714285   = 0.0029761" (3 thou) shim added to align hole /castle

Note the above assumes the gap in the nut has gone passed the hole in the shaft so the nut needs to turn anticlockwise which will be achieved when adding the thickness shown.  You can use a thicker washer which is a multiple of the slot to slot size + the extra fraction of slot to slot size required.  This may be necessary if the nut is going too far onto the shaft so the hole is or is nearly beyond the castellations.

Also to note, nuts may be flange....these are the better ones to use.

(and lastly...don't forget to put the washer in after the oil seal and BEFORE the bearing!..........ah ok I should have put this first  )

Dennis

Hi Dennis, I've a small number of new 1/8" x 1.1/2" and 9/64" x 1.1/2" imperial split pins should you need any.  If these are of interest, PM me your address and I'll pop a few in the post.

***EDIT*** I've just measured these new 1/8" split pins with a metric micrometer and they appear to be 2.93mm. The next size up that I have are 9/64" x 1.1/2" - these 9/64" would appear to be 3.49mm measured with a metric micrometer.

Jeff.

[Bob Culver]

The split pin only functions when things are failing.  Even without the nut  the wheel cannot come off.  Keeping the taper tight, more important on the Seven axles, is much simplified with no pin or one outsde of the nut. (the main problem then is that when regularly tightende the tapers become almost immovable with the standard puller!)

[Speedex750]

I'm with Bob on this; my heavy '38 axle has the nuts done up F tight with no split pins. It's the tightness that retains them, not the split pin.

Dave

[bob46320]

I don't think I have ever seen a split pin shear off on any castelated nut due to the nut loosening, whatever the diameter of the pin (within reason). If the nut is really tight, and you can't get the correct size in, put a slightly smaller pin in.

[Colin Morgan]

Hi - When the wheel was off today, measured the thread diameter of the 'heavy' half shaft - 19.0mm - so 3/4" BSF (19.05mm) - couldn't see enough threads to count TPI.

Colin

[Dennis Nicholas]

Thanks to all for replies.  Hedge cutter cut phone line yesterday and wonder of wonders......fixed today......must be a record!  The joys of country living.
I have just ordered pack of 10 A2 stainless pins  3.2mm X 38mm from gwr-fastners on ebay for £1.85 free delivery arriving before 3 Oct.

My hubs were ground onto taper last time off many years ago and under the use of a 948cc BMC A engine have remained tight.
My big problem is that my 2 little A7 spanners (bearing nut and hub nut) do not fit in the Nippy tool pack easily so I have to hope I don't need them away from home.

   

   

Denis

[Dennis Nicholas]

Split pins received and they are a nice fit.
Just a thought....well aware of taper taking drive.....split pin not really needed.....etc........if pin fitted it would prevent the possibility of the nut (special thread) from coming undone and being lost.........seem to remember someone posting that happened to them? Of course that would only happen if no wheel centres were fitted.

[Bob Culver]

To avoid the hassle of fitting and possibly refitting the nut drill a split pin (or wire) hole outside of the castellations.
Especially on the earlier hubs regular checking of the nut gives an indication of the state of the taper. Should immediately or quickly stabilise. As before the main problem is then dislodging!