Swingarm cracked...

utopia · 29-08-2023, 01:25 PM

Blimey.
I shudder to think how that could have ended.
No doubt you've had the same thoughts.

I remember someone else reporting the same sort of failure (on this forum) a few years back but I can't remember who it was.
Of course its difficult to know for sure without knowing the previous history (torque settings etc) but I'm going to stick my neck out and say that it could well be a borderline weak point in the design ... which is worrying for the rest of us (though admittedly there must be many thousands out there which haven't failed).
Certainly it does look visually like there is minimal metal in the area in question.
And I'm pretty sure you will have followed the recommended torque settings (though no telling what a previous owner may have done).
Also I can't decide which I think is more likely .. overtightening being the direct cause of failure or maybe undertightening (or more likely a slackening off in use) allowing the assembly to "rattle" (in a minimal way).

Personally, I think I would be reluctant to trust a repair.
No matter how good the weld penetration is, I would always be worried that it would be less than perfect which wouldn't be good in an already (possibly) borderline area.
You would probably have to recut the spindle bore anyway, which wouldn't be easy.
Of course on the other hand, maybe a repair could beef up the area .. I dunno if there's much room.

On balance I'd be inclined to fit the other arm.
I don't think I'd bother with the brace either .. I suspect you'd agree that its mostly cosmetic, on a road bike at least.

29-08-2023, 01:25 PM	#12
utopia No turn left unstoned Join Date: Jun 2010 Location: leicester Bike: M750 Posts: 4,545	Blimey. I shudder to think how that could have ended. No doubt you've had the same thoughts. I remember someone else reporting the same sort of failure (on this forum) a few years back but I can't remember who it was. Of course its difficult to know for sure without knowing the previous history (torque settings etc) but I'm going to stick my neck out and say that it could well be a borderline weak point in the design ... which is worrying for the rest of us (though admittedly there must be many thousands out there which haven't failed). Certainly it does look visually like there is minimal metal in the area in question. And I'm pretty sure you will have followed the recommended torque settings (though no telling what a previous owner may have done). Also I can't decide which I think is more likely .. overtightening being the direct cause of failure or maybe undertightening (or more likely a slackening off in use) allowing the assembly to "rattle" (in a minimal way). Personally, I think I would be reluctant to trust a repair. No matter how good the weld penetration is, I would always be worried that it would be less than perfect which wouldn't be good in an already (possibly) borderline area. You would probably have to recut the spindle bore anyway, which wouldn't be easy. Of course on the other hand, maybe a repair could beef up the area .. I dunno if there's much room. On balance I'd be inclined to fit the other arm. I don't think I'd bother with the brace either .. I suspect you'd agree that its mostly cosmetic, on a road bike at least.