Author Topic: torsion bars  (Read 342 times)

0 Members and 1 Guest are viewing this topic.

Offline tck

  • Senior Member
  • ***
  • Join Date: Jul 2004
  • Posts: 344
    • old racer
torsion bars
« on: 25 May 2020 at 10:10 »
I have just come across another strange thing on upending my frame I am sure the two torsion bars are dissimilar sizes one moves a bit the other rattles like a spoon in a bottle neck
 I know they were changed (beefed up)  in later production but I glean that miss matched bars are an absolute no no
Well at this distance in time I am hardly in a position to either make or obtain a matching bar so how much of a no no is it?

Offline eddie

  • Master Member
  • ****
  • Join Date: Mar 2006
  • Posts: 1656
  • Location: Hampshire, UK
Re: torsion bars
« Reply #1 on: 25 May 2020 at 12:07 »
As far as I am aware, there were 2 strengths of torsion bar available from the factory. There was the standard bar fitted to most road machines, and the heavier bar that was standard on the 'Plus' machines - these bars were often retro-fitted to road machines if pillion passengers were regularly carried. The easiest way of differentiating between the 2 types is to measure the diameter of the bars - the standard bars are 9/16"dia, and the 'Plus' bars are 5/8"dia. The bars were also colour coded to denote which side they were fitted to - on the presumption that they would 'settle' during initial use. Evidently, the codes got changed during the years of production - so that adds even more confusion.
  If one of your bars feels tight in the frame, check out the straightness (is there such a word?) of the bottom frame rails. With the rear suspension knuckle removed, you should be able to clamp a packer and straight edge to the suspension pivot tube and see if the frame tube is parallel to it. I am of the opinion that rear suspension pivot seizures are the cause of most of the frame breakages. Mr Douglas's pivot pins were drilled right through, so pumping in grease just jacked the core plug out of the swinging arm lug (rather than push grease through the tight bearing). When we were involved with Club spares we modified the design of the pins to have a blank end, so the grease had no option but to go into the bearing.
   In answer to your last question - the fitting of odd torsion bars IS a no no. it would seriously upset the bikes handling, and also create even more complex stresses in the frame - the rear lug that carries the swinging arm pivot already suffers very complex loads that result in the known frame breakages. If you need to find another bar to make up a pair with one of your bars, and you are not sure of it's handing - fit it and ride the bike a couple of hundred miles. Then with the bike on the stand, remove one of the rear suspension pivot bolt to see if the holes still align - if not, try setting the end anchor onto another spline to get an improvement. The replaced torsion bar should only take the 'set' once and then remain stable.

« Last Edit: 25 May 2020 at 12:14 by eddie »