broken 76 qulbix swingarm

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John Bozi   1 MW

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broken 76 qulbix swingarm

Post by John Bozi » May 29 2021 8:31pm

broken swingarm.jpg
broken swingarm.jpg (101.36 KiB) Viewed 363 times
Just happened doing 5kmh. I put some weight on the suspension prior to attempting to lift the front up before a speed bump.

Walked home in shame :oops

The frame is about 3 years old. With signs of rust there. Not sure what failed first, the bolt or swingarm part.

markz   100 GW

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Re: broken 76 qulbix swingarm

Post by markz » May 29 2021 9:15pm

Do you think that would have happened on any of the major brand name bicycles?
John Bozi wrote:
May 29 2021 8:31pm
broken swingarm.jpg

Just happened doing 5kmh. I put some weight on the suspension prior to attempting to lift the front up before a speed bump.

Walked home in shame :oops

The frame is about 3 years old. With signs of rust there. Not sure what failed first, the bolt or swingarm part.

Jonno   100 W

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Re: broken 76 qulbix swingarm

Post by Jonno » May 30 2021 4:00am

Looks like loose bolt failure to me.
Where's the bolt from the other side?

Reminder: Regularly check nuts and bolts are tight :warn:



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John Bozi   1 MW

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Re: broken 76 qulbix swingarm

Post by John Bozi » May 30 2021 7:27am

I didn't bother walking back up the road and look for the other end of the bolt. I can't remember if the bolt was supplied by qulbix or I had to choose my own. The nut I had on it though was the type with that locking plastic bit, so it never unwound.

I have broken bicycle frames with mid-drive crabbing.

This bike though is relatively heavy but I never do jumps on it higher dropping off a gutter....

My own idea is a combination of a bolt not strong enough to do the job and steel that weakened due to rust.

question is do I repair it, replace or look for another frame.

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Re: broken 76 qulbix swingarm

Post by HK12K » May 30 2021 11:59am

That's not the fault of the frame. Unfortunately the bolt let go and the swingarm faced the consequence.

I'd bring it to a competent metal worker to be repaired, or contact Qulbix directly for a replacement. They'll sort you out

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John Bozi   1 MW

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Re: broken 76 qulbix swingarm

Post by John Bozi » May 31 2021 4:12am

I am not sold on a sure answer.

There is a lot of lever-action going on, and a slight increase angle might have twisted the bolt enough to snap it and then the full force killing those 'wings' on the swing arm.

I have emailed qulbix, asking for 'ideas'.

And I also do have a guy that welds really well... well if he is still doing it. Was a while ago I went into his shop.

If I go to repair I would for sure beef up. I am just not sure about the paint job after. What would I do instead of powder coating all that heated up area?

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pwd   10 kW

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Re: broken 76 qulbix swingarm

Post by pwd » May 31 2021 7:10am

For paint, if you go the repair route:

grind off/sand the area
wipe down with mineral spirts or acetone
buy some self etching primer (spray can) (sticks well to bare metal) and give it a few coats
then paint with whatever colour you like (spray can)

that should cost less than re-powder coating, especially if you have any of those materials
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Re: broken 76 qulbix swingarm

Post by TNC » May 31 2021 11:19am

OP, if I'm looking at your pic correctly, whoever designed those tabs thought it was a good idea to have "lightening" holes right down to the welded portion of the tab at the interface with the swingarm? And is it not welded on the inner portion of the tab to swingarm? Then again...are those shock tabs a folded-over component instead of a flat tab welded to the swingarm? If so, there's nothing like have a relatively thin piece of folded-over steel tab and only fully welding one side of it. You mention "no signs of rust", but I don't think that mattered due to the way they built and attached what appears to be a folded over piece of mild steel.

I would tend to lean toward the bolt coming loose first which then stressed the mounting tab. However, if the tab had been more robust and fully welded in place on both sides, you may have had a long period of time with some racket and clanking to give you warning before things let go. The bolt could have come loose and when it fell out, one or two articulations of the swingarm could caused that bend in the tab.

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Re: broken 76 qulbix swingarm

Post by John Bozi » May 31 2021 7:10pm

thanks for paint advice

TNC, I was just talking to my neighbour about it and we were saying exactly the same as you just did. The lightening holes are exactly where it bent the first bend. The line of that bend contains half the metal it would otherwise. And if I had the bolt on that line it would have been much better... lower with less levering possible...

He also said that it could have been better to have a U shaped part welded in there instead to the two parts... but anyways this is all detective speculation not getting me much further...

I use to think this frame was as good as it gets for the price. Heavy but strong where it counts... Not anymore.

Still waiting for a reply from QULBIX... otherwise, I'd see my fabricator.
Last edited by John Bozi on Jun 03 2021 11:16pm, edited 2 times in total.

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Re: broken 76 qulbix swingarm

Post by John Bozi » Jun 02 2021 2:24am

I got a somewhat rude reply from QULBIX pointing blame at the lack of the correct length bushing.

Yes I used spacers to complete the bushing to the ears.

I have also put the swingarm in for repair locally after that. The welder proposed the idea of angled supporting bits. He doesn't express himself much more than that and I am happy to chill.

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Re: broken 76 qulbix swingarm

Post by TNC » Jun 02 2021 9:18am

The good news is that it is steel and should be easily capable of repair and upgrading.

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John Bozi   1 MW

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Re: broken 76 qulbix swingarm

Post by John Bozi » Jun 02 2021 7:51pm

Yes,

I was thinking to cut it out and put in a new part, but 'Mannie' the fabricator, said he would straighten it up and weld in the angled supports... He's an older guy that sees things with different eyes spending so much time in that business, so I will give him a bit of leeway on the solution...

but I am still a little worried of having a cracked part being held up... Hopefully not killing me when I ride fast. :cry:

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