Cracked banshee rune

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Cracked banshee rune
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Posted: Sep 11, 2019 at 14:48 Quote
Hi, my son has a 2013 Banshee Rune which has a hairline fracture at the shock mount.I have heard on one side the new weld would be stronger than before and on the other hand the new weld will make the frame weaker.Is there anyone able to shine some light on this matter before I decide what to do one way or the other.

Posted: Sep 11, 2019 at 17:13 Quote
Banshee uses 7005 aluminum in the Rune. You can weld 7005 without post-weld heat treating. Find a welder who really knows what they are doing. I don't know the appropriate filler rod, but that is going to be important.

Posted: Sep 12, 2019 at 13:33 Quote
Ok will look I to it.I messaged Banshee 3 days ago but no reply yet.Thanks for the advice.

Posted: Sep 19, 2019 at 21:51 Quote
My son has a 2017 spitfire with a very small crack at the weld where the downtube meets the bottom bracket. We are the second owner and banshee is willing to hook us up with a crash replacement. Pretty awesome. But still about a $1000. I've been talking to an experienced welder who says no prob, grind it down and re weld. Then I talked with my trusted bike mechanic and he said don't do it, it will weaken it.
What to do!
Best of luck with the Rune. We love the spitfire.

Posted: Sep 20, 2019 at 10:02 Quote
We are having it welded,got nothing to loose.My son isn't the biggest of riders so I'd imagine the frame will deal with it.I had a Foes mono rewelded some years back and it kept going with no problems for years after.

Posted: Sep 23, 2019 at 9:11 Quote
Bike shops, bike mechanics should always ere on the side of caution.

The knowledge of Metallurgy is certainly not everyones expertise,
and that applies to a lot of welders, metal fabricators also,
and this is why you get conflicting answers.

Yes it can always be welded, will it stand up and last ???
and this is were the skills and understanding of Metallurgy
come in, a welder with this know how is key to whether it can
be welded to a reliable standard.

I had this problem with a purchased 2nd hand Specialized big hit 2,
which had a hairline stress crack on the topside of the down tube,
about 25mm across just behind a weld that joined both top,down tubes
to the head tube.

I contacted a number of welders, some, it was beyond there capabilities
as it needed to be TIG welded in aluminium, basic metal fabricators tend
to work mostly with MIG or Stick.TIG requires a different certification or ticket.

I was recommended a welder who works TIG welding, does motorbike frames and
custom mods, so was at least qualified to give an answer as to whether I could repair
my frame.

It was doable, however due to the nature in how aluminium moves it would not be as strong as was
before the crack, as the crack was stress related.
So it would be at my risk, I went ahead and took the chance.

To mitigate the heat treat, he used heat sink pads around the weld area to keep temp
down as much as possible, drilled holes either end of the crack, there was no V cut
to then fill with weld, instead, he burnt the weld through the crack allowing it to build up
on the inside of the tube rather than the outside.

End result visually, perfect will it last ? time will tell, though it was the best that could be done
with a weld repair. To mitagate it from failure the frame tubes will now be core filled,
this will slow or at least reduse stress resonance, and give warning to a potential frame
snapping and eating dirt as the core will hold it temporarily.

Posted: Sep 23, 2019 at 13:44 Quote
Interesting,what will the frame be filled with as per your last paragraph.

Posted: Sep 25, 2019 at 8:35 Quote
Polyurethane Foam as used in the marine industry,
its used as a carbon fibre (amongst other composites) as a core fill
for structural reinforcment of yacht bulkheads, floor decks etc,
anywhere that requires reinforcement of a hollow part that tends to be
made from a composite material and requires it to be lightweight.

I'm very surprised its not commonly used in carbon fibre bike frames,
as the additional benefits in added strength for the small additional weight
are greatly improved.

Posted: Sep 26, 2019 at 18:08 Quote
Some frames are made with a foam core but then it gets removed, for weight, using a chemical to dissolve it. Others use bladders.

Hope fully the new design of rune won't crack.

Posted: Sep 27, 2019 at 6:05 Quote
"Some frames are made with a foam core but then it gets removed, for weight, using a chemical to dissolve it. Others use bladders"

Thats for the purpose of manufacture, I would have thought for the gains in strength
and durability, ecpecially crush damage, that a lightweight core would benefit in
so many areas.

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