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Broken Tensile Freewheel


Mowgli

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Hey,

Tried searching but couldn't find anything, apologies if i didn't look hard enough.

my freewheel died today, not by skipping but by a third of the chain ring outer breaking clean off, see pics below......

n516357730_1101067_2197.jpg

n516357730_1101068_3370.jpg

n516357730_1101069_4303.jpg

What could this be caused by?

Has anyone had this happen before?

Regards

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I'm pretty sure that it was just on one batch of them where the outer race was too brittle, just ring up Onza, I think they offer a free replacement, if not then it'll be the half price replacement.

could be...very hard to tell from the pictures, but considering the time you've had it and how it's broken, it probably was just a brittle fracture- possibly a batch weren't heat treated properly...

to be honest...i'm not sure how much effort onza put into investigating this sort of thing, but if it's happened to others (as the above suggests) they may consider replacing it. They did not like the idea of me looking at my broken cranks under an SEM...wonder what they were afraid of...:P?

adam

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That looks like fatigue cracking with a ductile final failure. It's blurred, but there seems to be a discoloured area in the broken cross section which indicates an initial crack that was growing over time. The white grainy surface is a ductile failure in the remaining material. A brittle failure would have a shiny faceted surface... Nice work BTW :)...

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That looks like fatigue cracking with a ductile final failure. It's blurred, but there seems to be a discoloured area in the broken cross section which indicates an initial crack that was growing over time. The white grainy surface is a ductile failure in the remaining material. A brittle failure would have a shiny faceted surface... Nice work BTW :)...

Well la, dee, da mr. Engineer :P

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i'm not so sure... this picture: shows a thumbnail shaped darker area like you said (maybe fatigue...maybe just grease?)...but there's no way that it's a ductile failure in my mind..

Got to agree with Adam, Doesn't look to be a ductile failure. But i have heard of a few going like this, as has already been mentioned there was a batch that seemed to have this problem.

Adam

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I believe Tom Booth had the same problem with his, think it was only a few days old aswell :ermm:

Twas me indeed I broke 3 :)

I'm pretty sure that it was just on one batch of them where the outer race was too brittle, just ring up Onza, I think they offer a free replacement, if not then it'll be the half price replacement.

The outer race missed the final stages of heat treatment on a batch, hence there prone to shattering etc (from the works of Joe at Onza)

Nope :)

Glad you didn't. I went face first into the wall I was gapping too. Bloodey hurt aswell :P

Here's my first attempt thou...

post-5803-1230472151_thumb.jpg

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The outer race missed the final stages of heat treatment on a batch, hence there prone to shattering etc (from the works of Joe at Onza)

post-5803-1230472151_thumb.jpg

haha...so sad i know...but that's exactly what i thought of- i was recently involved with the failure investigation of a high pressure steam valve casing from a power station in pakistan...exactly the same problem :S..

shoot me?

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Something similar happened to me with a really cheap freewheel called esjot in 1995. The weird thing back then was that, after it exploded, I couldn't find any part of the outer chainring anymore. It exploded in a way that the pieces got lost somewhere in the lawn. And I bit a pallet. yummy. (ouch)

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I've not seen anything like that before, apart from my old dicta after i cut if with an angle grinder to get the fecker off my cranks. Just recently got a tensile though, so i hope it don't go the same way as above....

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Iv snapped 3 ACS claws like this back in the day, and one of my tensiles done the same lol, not a clue why...

Is it FFW that your running btw? If it is, maybe its that thats causing it?

King :)

edit: haha, TF wont let me type F T W without it going into the stars like ***

Edited by terror-error
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