Fork centres

[Nomad54]

Can anyone tell me if the fork centres differ on the a10 and the a65

[limeyrob]

Just been measuring as my A10 looks to have A10 yokes and legs with an A65 wheel.  The answer seems to be "yes" if they are 6 3/4", no if you have 6 1/2"  My yokes are probably 1959 and the wheel 1968.

[Swarfcut]

 Early versions of the A50/A65 use the A7/A10 type full width cast iron hub along with the same spindle, 42 5824. So both ranges appear to have mounting points at the same centres, hence Rob's easyfix swap even with a later wheel.

 Swarfy.

[limeyrob]

Its seems Triumph owners get similarity confused by the number of fork and wheel changes so a guy named Mike James has produced a guide.  All I can say is "thank you" as it saved me a lot of time trying to work out the A10/A65 fork - wheel - spindle quagmire.  Most of the dimensions (if not all) seem to be the same as the BSA ones.
With acknowledgment to Mike:
https://hermit.cc/tmc/technote/mjames/forkin_forks/susp_t120_fork_dimension_changes_for_1968_and_1969_mjames.pdf

[Swarfcut]

 Another trap for the unwary is that although BSA and Triumph shared the same parent company, and a certain amount of common design features would be expected, the cast iron front hubs are not identical castings, there is a different number of ribs on the drum.

 Also that bargain jumble Triumph pre-unit hub complete with bearings and spindle won't fit your A Series BSA without changing the spindle.....the clamp bolt indents differ by 1/4", and the spindle  from Triumph is just that bit shorter. Everything else is more or less a straight swap, as noted.

 On a pair of later A10 sliders to hand(with two stud Y  plate mudguard mount) the spindle lugs are offset towards the centre of the forks, so the indent for the spindle clamp bolts are not on the centre line of the fork tubes.

 Swarfy.

[limeyrob]

Yes, I spent a lot of time looking at that picture of wheel spindles trying to work out what was going on!  Confusingly the shortest of the spindles was a perfect fit in my 6 3/4 centres forks.  I think because (as you say) the bottoms of the fork legs are offset towards the centre.  The peg and the 1 19/64 vs 1 27/64 does match up but unfortunately I have the 1 19/64 and need the  1 27/64 so its off to the welder to get the missing 8/64....

[BagONails]

It does make you wonder in amazement that they ever got a bike out the door - what a carry on!
Too easy to criticise in hindsight of course but blimey!

Then of course there was the issue with the front and rear wheels being out of line by design (Something to do with the A65 engine positioning across the frame and getting a decent chain line) and then when the Americans moaned because the A65's were tracking towards the centre of the road all the time i.e. into the oncoming traffic. (riding on the right meant the misalignment worked with the road camber rather than against...) They then decided to cant the front wheel over in the forks by 1 degree to counteract it.

So the wheel spindle bores between right and left hand A65 forks, I figure on the later models, are actually deliberately bored out of line.  At least so I've been told...

You couldn't make it up could you?

[mikeb]

no expert here but as i understand it, all bsa forks were 6 3/4" spacing - A10 and A65s.
BUT spindles, hubs and sliders can differ: the 1968 A65 used a narrower '37-1641' spindle to accommodate the 'new' triumph hub/TLS into the 'wider' bsa forks by using offset end caps in the sliders - THAT YEAR ONLY. (So the '68 A65 forks are unique to that year - but the fork spacing is the same.)