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Re: crank arm snapped - what to replace with? [tigermilk] [ In reply to ]
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tigermilk wrote:
JoeO wrote:
I have always wanted to say "I broke my crank arm".

Well, if you have Shimano Hollowtech you are more likely to break one.

Not with my watts.
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Re: crank arm snapped - what to replace with? [tigermilk] [ In reply to ]
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I've seen the plethora of breakages on the recent 4 bolt cranks but not on 5 bolt. I have a couple of 6600 and 7800 cranks and think very highly of them. Fantastic value if you buy used.
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Re: crank arm snapped - what to replace with? [bm] [ In reply to ]
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a nice thought, but not likely.
if tail of FD is out 'that much', a single pedal stroke will destroy that cage at best. This is a brazeon FD so not likely to be a cm or more out. and if so, then entire brazeon will also be twisted.

While with a clamp on FD there can be in extreme situations the entire clamp and FD assembly gets waaay out of alignment (uh...yes...I was JRA mtb and..uh...I think it was a stick! but I think I whacked it with my heel) but the chain will foul everything up in a heartbeat.

Anne Barnes
ABBikefit, Ltd
FIST/SICI/FIST DOWN DEEP
X/Y Coordinator
abbikefit@gmail.com
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Re: crank arm snapped - what to replace with? [ABarnes] [ In reply to ]
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You'd be surprised how common it is for a front derailleur to "rub" the inside of the crankarm. A front derailleur commonly has only about 2 to 3 mm of clearance from the outside of the cage to the inside of the crankarm when adjusted correctly. If it's adjusted just slightly off so that the lower edge of the cage is angled outward a tiny bit, it can rub the crank arm. It can be so slight that you don't hear it or feel it when pedaling, but after several hundred thousand pedal revolutions, that tiny little bit can score the inside of the crankarm. Whether that is enough to cause the crank to break, who knows, I just noted that the location of the break in the OP was about at that same location.
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Re: crank arm snapped - what to replace with? [bm] [ In reply to ]
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bm wrote:
You'd be surprised how common it is for a front derailleur to "rub" the inside of the crankarm. A front derailleur commonly has only about 2 to 3 mm of clearance from the outside of the cage to the inside of the crankarm when adjusted correctly. If it's adjusted just slightly off so that the lower edge of the cage is angled outward a tiny bit, it can rub the crank arm. It can be so slight that you don't hear it or feel it when pedaling, but after several hundred thousand pedal revolutions, that tiny little bit can score the inside of the crankarm. Whether that is enough to cause the crank to break, who knows, I just noted that the location of the break in the OP was about at that same location.

Did you not see the photo of the broken crank? I doubt that bike has been maintained even slightly. Crank was probably damaged in a crash or falling off the bike rack or something and the damage never noticed under the layers of grime.

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