Bike frame repairs

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mcrkennedy
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Postby mcrkennedy » 28 Nov 2008, 21:59

Hi folks

I need some advice. The rear dropout on the derailleur side of my bike has cracked in two. I have an alloy frame with forged dropouts. Question is can I get the frame repaired?

Part of me want the answer to be yes, the other part wants no to be the answer, or yes but it will cost a lot of money, as the finance committee will then let me get a new bike!!!

If I can get it repaired, then who and where?

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weiyun
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Postby weiyun » 28 Nov 2008, 23:08

Photos please.

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Toff
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Postby Toff » 29 Nov 2008, 02:09

When you say alloy, I assume you mean aluminium. I'm also going to guess that you have a clean break where your chainstay meets the dropout. This is a high stress point, and probably the most common place for a fatigue related crack to occur.

It can be fixed. You just TIG weld the 2 bits back together. Welding aluminium takes lots of skill, but your bike won't fall apart if the welder botches the job, since you probably rode around for a while on the broken frame before you realised...

No idea on cost, but it shouldn't be too expensive. It's probably no more than 20 minutes work, of which 19 is cleaning the surfaces. Talk to a framebuilder. Jim/Peter Bundy would be closest, but I think Paul Hillbrick is likely to be more experienced with aluminium.

Knowing the properties of aluminium though, I'd have a good think about getting a new frame. If you're riding a fatigued frame, something else could snap. The next break could be more dangerous, and unlike steel, aluminium gives you no warning before it fails.

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mcrkennedy
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Postby mcrkennedy » 30 Nov 2008, 13:06


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weiyun
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Postby weiyun » 30 Nov 2008, 15:32

Wow! Pretty impressive and an off place to crack based on what people commonly report.

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Toff
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Postby Toff » 01 Dec 2008, 10:58

Wow! Pretty impressive and an off place to crack based on what people commonly report.
This crack is exactly as I predicted in my post above. Very common break & fixable.

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weiyun
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Postby weiyun » 01 Dec 2008, 11:06

This crack is exactly as I predicted in my post above. Very common break & fixable.
I've seen many photos of fractures towards the rear of the chain stay and the hanger extension, but none of the actual drop-out piece.

Learn something new everyday. :D

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Toff
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Postby Toff » 01 Dec 2008, 11:37

I have a hunch here, Michael. Take your rear wheel out, and remove the quick release skewer. This sort of break is common when you ride with a broken rear axle. These days breaks in dropouts are less common, because cassette hubs make the rear axle less likely to break, but that's your most likely cause. Over the years, I've broken 2 frames at the right rear dropout. Both times I had been riding on a broken rear axle without realising.

Even if the axle is not bent or broken, it has almost certainly has been flexing, and this is what causes the dropout to fail, so getting a better rear hub will prevent it happening again.

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mcrkennedy
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Postby mcrkennedy » 01 Dec 2008, 11:56

Chirs

Thanks. I will get it checked. It is an Ultegra hub and it does seem to run true but I will get it checked out.

Michael

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mikesbytes
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Postby mikesbytes » 01 Dec 2008, 12:45

That type of crack is also common when the rear has been put under violent stress, such as stacking it and the bike doing somersaults, the sort that would wreck the rear wheel.

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weiyun
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Postby weiyun » 01 Dec 2008, 12:50

That type of crack is also common when... the bike doing somersaults...
I think Michael has been secretly training for these maneuvers on Hawthorn Pde at the crack of dawn.

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mikesbytes
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Postby mikesbytes » 01 Dec 2008, 13:00

I think Michael has been secretly training for these maneuvers on Hawthorn Pde at the crack of dawn.
I wrote off a frame in 2001 when I had a head on collision with another bike at the southern end of the Harbour bridge. I did a sumersault thru the air and landed on my back but only ended up with superficial grazes. The bike fared much worse.


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