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When a uni-body frame is bent or distorted there is a limitation to how much damage can be repaired and have the frame retain at least some of it's initial integrity.

As well, the procedure to actually straighten the frame, from what I understand, is actually a component of the limitation to repair the frame.

Can someone explain the procedure and mechanisms used in the frame straightening process as well as the limitations?

How does a technician that is charged with straightening the frame measure whether or not the frame can be repaired?

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  • If you haven't done so, check out the videos on YouTube ... there are a lot of them out there showing frame straightening. This is definitely one area I don't really have a clue about, other than the basic procedure of hooking up a bunch of chains and hydraulics and putting a real hurt on the vehicle, lol.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Apr 18, 2015 at 0:12
  • @Paulster2 I've consumed a bunch of those vids. Love to watch them. Sometimes it seems a little dangerous. I'm really interested in what it is that makes a shop say, "nope, can't be fixed because of X." I can look at a unibody that crunched up in a ball and pretty much know it's beyond repair but have no idea of what beyond repair really means.
    – DucatiKiller
    Apr 18, 2015 at 0:32
  • @JoshCaswell I don't know of any unibody motorcycle frames. The only type I'm aware of are for cars.
    – DucatiKiller
    Apr 26, 2015 at 19:46
  • Also "fixable" is culturally determined. I know lots of unfixable uni-bodies on copart in the US get sold to Central America where they are repaired and sold. But then there are stories of people hitting bumps and having the car split in two as well.
    – Ukko
    May 13, 2015 at 14:07
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    @Ukko - culturally determined is not acceptable. I'm not interested in the social aspects of unibody frame repair. I'm interested in what are the determining factors regarding a repair event. These are mutually exclusive. Not interested in discussing a 'Frontline' script. More interested in an episode of 'How it Works'.
    – DucatiKiller
    May 14, 2015 at 8:04

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Having finally had the frame on my Yamaha 750 Super Tenere, straightened on a jig and re-welded, I have some info from the guys who did it:

  • The two methods they use are tension - pulling using chains, and pressure - hydraulically forcing the frame to conform to a template.
  • For minor deformation, it's a relatively safe bet with modern (and reasonably old frames) that steel will cope. Obviously certain more exotic materials won't - it's down to malleability and brittleness; the science of elastic and plastic deformation of metals
  • Welds are more likely to be brittle than structural members, but are more replaceable, so a crash that has snapped joints may actually be easier to recover than one where the members have all suffered major bends
  • Because of the various angles, welds, cross members etc in a frame, they don't rely on any actual maths to identify whether it will be recoverable - they rely on experience. A major crash may be an obvious no-no, and a very minor dunt may be obviously easy, but that dividing line is tricky - and they work on a scale of more or less likely...and then just try it
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  • Love that you straightened out a Super Tenere! None of those here in the states. Really interested in car unibody straightening methodology and risk. Upvoted you for sure. Thanks!
    – DucatiKiller
    May 14, 2015 at 8:05
  • I would have actually loved to have seen it, but they had to strip everything off the frame in order to do it, so I didn't have time to stick around. Yeah - car unibodies are going to be different in a whole host of ways but I have no info on them - just thought this would be a useful datum point. Can't wait to get it back on the road this summer!
    – Rory Alsop
    May 14, 2015 at 8:09
  • Indeed. I just got hit on my Aprilia and am in the process of attempting to make it better, reason.....summer riding. Cheers!
    – DucatiKiller
    May 14, 2015 at 8:10

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