Steering spacer tube .

Time Warp said:
Why would they be inaccurate?
The frames were built by specialised companies in large numbers. (Over 50000 Commando frames not including spare parts frames)

The steering head is a heavy wall tube.
Station 1, face one end leaving 0.020" of cold sawed green on the other. (Or both ends could be done but is easier done at Station 2)

Station 2, the faced end goes against the positive stop which could be the chuck face, the outer end is faced to zero (the 0.020" green) with the boring tool then bored to depth.
The part is flipped, seat to the stop and the other cup bored.
In the case of the Commando the two cup depths are different but off Zero they could be within 0.002" to each other easily.
Maybe 45 seconds to do both cups in batches of 100's.

It would have been very interesting to have done a tour of the factories, both manufacture and assembly back in day and always seemed odd to have never seen a post from someone who worked on the shop floor, not the office.
Click to expand...
If the steering head tube was precision machined first, I wonder how the bores were kept from distorting during the welding process
 
I suspect Bert is correct, the finished specifications would vary for a variety of reasons, inconsistent welding being one of them. We could probably add to the list: clapped out equipment, unmotivated employees, least cost subcontractors, etc.
My guess is after the bearings and spacer tube were installed at the factory, in use the front end would pound the assembly until something resembling a workable fit develops.
 
Last edited:
When fitting new ball bearings on my commando the biggest problem I found was removing the powder coating. Who ever built my bike prior didn’t do this so the lower bearing was never seated properly.
 
BERT said:
If the steering head tube was precision machined first, I wonder how the bores were kept from distorting during the welding process
Click to expand...

I need to go and get mortar for my Bessa block raised garden project.
I will post my thoughts on that as a time served Boilermaker/Welder and hobby machinist later in the day.

Steering spacer tube .
 
on the repro JPN racers that Peter Williams was making, they assembled the frame, then did final boring of headstock on a massive horizontal mill, all to make sure it was ‘straight’.
 
jan nelder said:
on the repro JPN racers that Peter Williams was making, they assembled the frame, then did final boring of headstock on a massive horizontal mill, all to make sure it was ‘straight’.
Click to expand...
I believe Mr Molnar does the same on his Manx frames (the precise straightness of which he is somewhat proud of). Certainly seems like the best idea to me.

I know some ‘old skool’ frame builders back in the day used to linish the OD of the bearing outer to be a precise fit in a less than precisely round tube.
 
BERT said:
Cool!
Click to expand...

I went though some hard drives that have pictures of frames I have modified including removing steering heads and replacing them with replacements welded back in at reduced rake angles, but it is not really of any use to this thread.
 
On the OIF BSA/Triumph frames the headstock bearing bores were machined after the frame was welded up on a rather large boring machine. There is a picture of the machining operation in a Motorcycle mag when reviewing the Triumph 650 OIF bike in 71.
 
Just for some historical accuracy.
Both of my Commando's had notchy bearings with as little as 20000 miles on the clock.

Thank the good lord I got rid of that hammered together by the factory abomination. :)

Steering spacer tube .


At least this thread gave some much-needed traffic to the website even if it was all over the show.
 

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