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My broken crankarm (Warning: Injury pic)

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Road Cycling “It is by riding a bicycle that you learn the contours of a country best, since you have to sweat up the hills and coast down them. Thus you remember them as they actually are, while in a motor car only a high hill impresses you, and you have no such accurate remembrance of country you have driven through as you gain by riding a bicycle.” -- Ernest Hemingway

My broken crankarm (Warning: Injury pic)

Old 09-15-08, 10:07 PM
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bigd
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My broken crankarm (Warning: Injury pic)

This is what happened to me yesterday..



It happened while climbing a 7% grade in standing position at a relatively slow speed.
That is the second crankarm to fail on me on this bike.



The Break occurred at 2 1/4" up from the end of the crank. Not at the bolt or fastening locations where I would imagine a break should occur in a cast piece.



Now i have 19 stitches in the side of my knee. The surgeon said I was lucky not to damage any muscle or tendons in my leg. The end of the broken arm was rather short. Luckily, I remained on my feet and the pedal disengaged as my foot hit the ground.

Looks like Bontrager owes me a new crank. I think I'll try shimano.
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Old 09-15-08, 10:09 PM
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That OCLV carbon sure is stiff!
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Old 09-15-08, 10:10 PM
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19 more reasons not to trust carbon?
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Old 09-15-08, 10:10 PM
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Ouch. So I assume the part of the crank still attached to the bike cut your knee open? Was anybody around to help? That blows man.
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Old 09-15-08, 10:18 PM
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Originally Posted by uke View Post
19 more reasons not to trust carbon?
those bontrager crankarms aren't their carbon model genius. aluminum probably, i had the same ones on my 5000. the lbs would probably-definitely warranty that.
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Old 09-15-08, 10:23 PM
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Originally Posted by PeddlingPilgrim View Post
those bontrager crankarms aren't their carbon model genius. aluminum probably, i had the same ones on my 5000. the lbs would probably-definitely warranty that.
How's that work?

Heal up, replace the crank and get back out there.
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Old 09-15-08, 10:42 PM
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Originally Posted by Copperhed51 View Post
Ouch. So I assume the part of the crank still attached to the bike cut your knee open? Was anybody around to help? That blows man.
It was the ugly part on the bike and it snapped right at the top of my down stroke. When your pedal breaks off the opposite pedal immidiatly bottoms out and turns the other into a spear. Luckily I was riding with my sister (who witnessed the whole thing) and we were only 8 km from her house. I immediately assessed my wound as being pretty serious and removed my gloves to put in the wound and held pressure on. After the bleeding came under control, I calmed my sister down and sent her home to fetch her car to take me to the hospital. This happened in the city still near down town. Only 2 cars stopped to ask if I was ok as I stood hunched over on the road side for about 15 minutes. About 30 other cars passed by slowly to check me out and 1 female cyclist who cylced off after I assured her I had help on the way.
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Old 09-15-08, 10:44 PM
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The doctor probably found it convenient that your legs were pre-shaved.
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Old 09-15-08, 10:48 PM
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Its hard to know exactly what I'm looking at but it does look to me like there is a forging fault right there where it has broken. It looks like the molten metal had some debris in it but the poured it anyway and then painted it black. I think I would only be using polished, plain aluminum cranks from now. They couldn't hide such a fault with paint and it would have to be rejected.

Regards, Anthony
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Old 09-15-08, 10:51 PM
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This kind of stuff never happened when we were kids.
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Old 09-15-08, 10:52 PM
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Holy crap!! So does anyone know what cranks don't randomly break? So far shimano and bontrager are on my do-not-ever-use list.
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Old 09-15-08, 10:53 PM
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jesus man... well at least it will make for a good story.
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Old 09-15-08, 10:53 PM
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Originally Posted by Copperhed51 View Post
The doctor probably found it convenient that your legs were pre-shaved.
actually, you could call me a natural born cyclist or swimmer or whatever, because I actually do have hair on my legs. the hair is blond and really fine.. I didn't have to start shaving my beard until I was 30.. Id post the other injury pic that is a close up enough see hair, but no.
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Old 09-15-08, 10:53 PM
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Originally Posted by Richard_Rides View Post
This kind of stuff never happened when we were kids.
Probably has something to do with new lightweight materials. I wonder what failure rates are like with older 60's-80's stuff?
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Old 09-15-08, 10:55 PM
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Your problem...it's a bontrager triple.

Sarcasm aside, that's one nasty cut from a crank arm. You said this is the second crank arm? Is this the same type as the previous? That has got to be a defect, that's something I would take up with Trek/Bontrager and complain about demanding they replace it, hopefully with something different and better.

Sucks you won't be able to cycle for a while.
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Old 09-15-08, 10:56 PM
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Originally Posted by bigd View Post


The Break occurred at 2 1/4" up from the end of the crank. Not at the bolt or fastening locations where I would imagine a break should occur in a cast piece.
Classic fatigue failure. The origin of the failure is dark/shiny from many repetitions growing the crack infintesimal amounts each cycle, then become the larger visible individual "waves" you can see where the crack was propegating quickly on the last couple dozen pedal strokes you made before failing catastrophically.

My question: are the black lines radiating from the defect point cracks?! That would be a serious defect - like lawsuit serious even (NOT suggesting a lawsuit, just saying it's pretty serious). They kind of look like some kind of fluid that got on there afterwards though. Blood, maybe? Eww.

And it's almost certain those cranks were forged, not cast.

Hope you are able to get back on the bike soon.

Mac

Last edited by sac02; 09-15-08 at 10:59 PM.
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Old 09-15-08, 11:07 PM
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the tell-tale "beach marks" in the top picture show that the crack had propagated through over half of the crank arm before finally failing. Who knows how long the part held out. An unpainted part would have made it much easier to see the crack, if it was gone over that is. Posts like these should make people with bikes new and old go out and clean there bike to check critical areas like the cranks bars and stems. I've got a box with Cinelli stems that are cracked all the way through by the pinch bolt where there is a huge stress riser.

Just curious but did the crack start at a point where the shoe contacted the crank-arm? check the pieces for scuffs in paint. Aluminum is much more notch sensitive than steel, or carbon! Older cranks back in the days of straps and toe clips would often fail where the straps would rub the crank. Another area is the threaded area for the pedal spindle.

Take off the pedal on the drive side arm and clean it thoroughly, check for cracks in bright light!

Heal quickly!
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Old 09-15-08, 11:17 PM
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Mac beat me to it! try another picture of both ends of the failed part. Use the Macro setting on your camera, often a picture of a tulip. That way the part will be in focus and not your hand!

It's also possible that the part was damaged during machining. Buffing or grinding incorrectly can overheat the part and actually change the properties of the alloy for the worse. Someone help me out, I know that in steels and Ti it creates Martensite. What about aluminum alloys?
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Old 09-15-08, 11:20 PM
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Originally Posted by wcoastbikr View Post
Your problem...it's a bontrager triple.

Sarcasm aside, that's one nasty cut from a crank arm. You said this is the second crank arm? Is this the same type as the previous? That has got to be a defect, that's something I would take up with Trek/Bontrager and complain about demanding they replace it, hopefully with something different and better.

Sucks you won't be able to cycle for a while.
Same type of fracture in same location on the same model of crank. In fact I brought the first broken unit into my lbs to show the owner. He looked over my pedal and frame for evidence of a crash and promply grabbed a new arm off the shelf and installed it free of charge saying that it must have been a rare defect as he had never seen an arm break in that location. It had about 10,000 miles on it at the time.

My next bike will be a double. This was my first road bike.
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Old 09-15-08, 11:20 PM
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Kinda makes me paranoid! I hope you make a quick recovery
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Old 09-15-08, 11:20 PM
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green - casting defect

orange - fatigue pattern

red - clean break

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Old 09-15-08, 11:23 PM
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2nd botrager crank? go SRAM ;D
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Old 09-15-08, 11:34 PM
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Originally Posted by mazdaspeed View Post
Holy crap!! So does anyone know what cranks don't randomly break? So far shimano and bontrager are on my do-not-ever-use list.
I have a Bonty crank on my E7 TT bike, and the arms flex noticeably (junk). I also had a Bonty Select rear wheel go bad (more junk; spokes were pulling out through the rim, catastrophic failure waiting to happen!) I will not buy Bonty, period. That crank is going by-by this winter.

I know, the rim was a production defect; it was replaced for a "$10 handling/mount the cassette fee" by the LBS, after they told me it was a free warranty replacement. The new hoop is on my wife's bike. I just do not like Bonty stuff.
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Old 09-15-08, 11:47 PM
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This is as good as my macro shots get.. I was in a hurry to snap pics before I left to work and deliver the bike to the lbs.

Looks to me like the long cracks radiate from one of the black blotches along the edge. The black stuff looks like it may be some blackening or chemical used in the chroming process that seeped into the pores from the outer surface. It did occur where my shoe would rub if I didn't use clipless. I also did clean my bike as recently as Friday night and didn't notice anything out of the ordinary, in fact, there is hardly a blemish on either crank. Smooth and shiny. This crank arm managed to make it over 24000 kms.
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Old 09-15-08, 11:53 PM
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Ouch...sorry to hear that.

Nice shiny alu cranks also fail sometimes (although I still thin DA cranks are really good!)

https://www.bikeforums.net/road-cycling/465175-oh-snap-ii.html
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