bent swinging arm

[spyke]

Hi chaps,
Latest saga of my build a bike from parts(wish I started with a whole bike but too late to go backnow!)
Swinging arm is bent from halfway down one side Ive just discovered, not sharply and could only tell when two halves of wheel spindles wouldnt line up, by quite a bit(half width hub type),Ive only got one SA so do i bend it cold or hot!(at my own risk obviously)
Cheers Spyke

[RichardL]

Risky offering opinion on whether to bend hot or cold without seeing the bend. Regardless, straightness of the swingarm is critical to a good ride and safety. I think I would try to, at least, get a price from a professional frame straightening house. You could also ask them what they plan to do. They should have no trouble offering that advice without compensation.

Richard L.

[Goldy]

Straightening tube is difficult. I would get another swinging arm from an autojumble or ebay.

[Shepherdfamily5]

I’ve started the task of changing my swinging arm bushes and on closer examination now unsure how straight my swinging arm is? One side of the arm looks a little higher that the other from looking at the rear. Doing my best to measure it I would say the difference between the two measuring at the spindle slots is about 5 mm. Am I being paranoid or is this is in tolerance?!

[limeyrob]

Sounds wrong.  What made you do the swinging arm bushes?  Its one hell of a job with a high risk of damaging the swinging arm.

[limeyrob]

Spyke - I'd replace with a used one.  Do you know how it got bend?  I would not trust one that had been bent and straightened.

[Swarfcut]

 Well now, you could say it is screwed as is and there is nothing to loose by attempting to straighten it.

   Bends in tube are always frowned upon by some, yet bent fork legs are regularly re aligned by established specialists, so it can be done.

  With the bushes removed, if you get that far, a mandrel and levels will establish if a problem actually exists, with the bushes still in place, how does it look within the frame? At the end of the day a few mm will make little difference on a bike used as most old bikes are ridden. Take the rear spindle as a datum, not the fork end forgings, see how that compares to the cross tube.
   A hydraulic press and a few supports will flex the trailing arms into line, a bent arm can also be coaxed back into alignment. If the arms are straight, it's just a twist in the cross tube.

 Swarfy.

PS Just read your first post. Registered with a "Scottish Number Plate" could be age related number allocated to a fine assembly of unrelated bits, so unless it's kosher, expect every malady known to the Forum.

[Shepherdfamily5]

The bike seemed to handle poorly and I put up with it. There was obvious movement in the rubber swinging arm bushes and now having removed it the rubber is all sticky and soft. It was only when I really examined it the difference in height between the arms was obvious so I have measured it as suggested across the spindle compared to the tube and the 5 mm difference was clear.

There is no obvious external damage to be seen, the frame is still in its original paint.

[limeyrob]

OK so the bushes have to come out anyway.  If you have access to a surface table and a press its doable.  The tricky bit is working out which bit is bent and bending that bit back, not adding a new bend.  This usually means heating the original bend to make sure that's where it bends the 2nd time.  Really workshop job. 

[Rex]

I've found old bike frames and parts to be surprisingly malleable and not difficult to bend at all.
A couple of bobbins turned up in the lathe to fit the bush end accurately, and the wheel spindle (or a length of well-fitting round bar) for the slotted ends, and a flat surface for accurate  measurement should be sufficient for checking which leg is bent.
The kitchen worktop is good, as long as the Boss is out for a while.