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Koga Globetraveller - broken rear fork

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Koga Globetraveller - broken rear fork

Old 02-05-18, 02:50 AM
  #1  
baboonst
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Koga Globetraveller - broken rear fork

Hello, I am a proud owner of Koga Globetraveller S You don't see many of them around anymore but it'a a real masterpiece and a joy to travel on. Yesterday I found out that a small bit of rear fork is cracked, to the point where it is almost comes of. This is aluminum frame - 7005 alloy - is there anything that can be done about it ? I work in a company that does aluminum welding ( on a industry scale ) and one of my collegues told me that they can weld it for me, and that this alloy is hmmm weldable.... but he is not a bike expert of course so I am asking you for an advice, is it worth it ?

Thanks

Jan
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Old 02-05-18, 07:15 AM
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Ironfish653
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Well, the frame was welded, to begin with, so I don't see why it couldn't be repaired by welding.

It looks like the 'fork' in in question is the ear where the rack mount attaches, so not a critical structural area.

You're going to lose the paint in that area, but if you're welder's any good, I'd say go for it.
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Old 02-05-18, 07:50 AM
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55murray
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Originally Posted by baboonst View Post
I work in a company that does aluminum welding ( on a industry scale ) and one of my collegues told me that they can weld it for me
Talk about being in luck!
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Old 02-05-18, 08:09 AM
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Well, the alloy is obviously weldable, since that is how the frame was put together in the first place. You could get it welded, but many (most?) welded aluminum bike frames are heat treated after welding. I'd be concerned about the repair weld not being heat treated, especially since the failure appears to be a fairly high-stress point on the frame.

On the other hand, what have you got to lose? If it fails again, you're no worse off than you are now.
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Old 02-05-18, 08:36 AM
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Originally Posted by Ironfish653 View Post
Well, the frame was welded, to begin with, so I don't see why it couldn't be repaired by welding.

It looks like the 'fork' in in question is the ear where the rack mount attaches, so not a critical structural area.

You're going to lose the paint in that area, but if you're welder's any good, I'd say go for it.

Look again. The suspension upper link attaches to the stay at the point of cracking. If I were repairing this I might consider a reinforcing plate of some sort as it's obvious that the OEM amount of material (if whatever condition it was after production) wasn't up to the task.


Generally I let riders pick their pleasures. If it's pink fuzzy seat pads or pink poka dot paint that will get one to ride then I'll help one find pink whatever. But this bike is ugly, sorry. Andy
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Old 02-05-18, 09:38 AM
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Look into Koga’s frame warranty. That might be covered.
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Old 02-05-18, 10:12 AM
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Metal fatigue happens, that reached a flex cycle limit..

As said above, go to your Koga Dealer, that you got the bike from.


[a hardtail will be more reliable]






....

Last edited by fietsbob; 02-05-18 at 11:25 AM.
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Old 02-05-18, 11:07 AM
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I used to work at a custom yacht builder of aluminum boats up to 70'. Many of the welders at that yard were highly skilled, having worked at New London building submarines where 100% of welds are ex-ray tested. It is customary in boat building to have a celebration of some sort, (beer and pizza) when the shutter plank is installed or in the case of an aluminum vessel, the last hull plate. Some of those guys could weld a beer can to the side of a hull with 1/4" plate. Your bike likely could be repaired by a skilled welder but I'd still look to install extra re-enforcement in some way.
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Old 02-06-18, 01:29 AM
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Originally Posted by Andrew R Stewart View Post
Look again. The suspension upper link attaches to the stay at the point of cracking. If I were repairing this I might consider a reinforcing plate of some sort as it's obvious that the OEM amount of material (if whatever condition it was after production) wasn't up to the task. .....
It's a linkage, but I don't believe it's part of the suspension, per se. The rear of the bike looks like a single-pivot design (pivot @ the BB) but it has vestigial seat stays so that it can fit the u-lock and a 'regular' touring bike rear rack. There's no other pivots apparent on the rear triangle, but if that is a 4-link, it's the weediest suspension linkage I've ever seen.

Now that I've been looking at it, I question the wisdom of having the rear rack mounted to the swingarm, that makes all of the cargo weight unsprung, and acting on those little stub 'chain stays' without the benefit of a full rear triangle, or the spring action of the suspension.

I will agree with you, that it isn't a particularly handsome bike, but if the OP's good with it, then i'll let it go at that.
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Old 02-06-18, 07:30 AM
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Jan, You've nothing to lose by welding that crack shut.
In addition I would drill pin holes at each end of the crack, add some re-enforcement extending beyond the "brake bridge", lubing the suspension plate, and determine if the rack is loading upper mounts unequally.

Brad

Last edited by bradtx; 02-06-18 at 07:32 AM. Reason: sp
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