jim beam said:
not a great pic. try another auto-focus setting to see if you can get
your camera to focus on the fracture surface. and when doing that, also
take a sideways shot of the arm too. i'd like to see the general
surface condition.
Agreed. I'll see if I can find someone to reverse the orientation of
the bike on the stand, which is adjacent to a wall. That will be allot
less cumbersome for me to take some more photos.
Quoted message said:cracks usually initiate at some form of stress riser. the newer shimano
cranks pretty much have the stress risers from manufacture/design under
control, but defects can still be occur in use. stone chips are common
in use and such a surface defect could initiate fatigue in a high
mileage component such as this. likewise, chain gouge is another really
common problem. i note that there appears /not/ to be the usual stop
pin on the big chain ring that usually prevents the chain dropping this
far down the crank arm. if the chain has dropped, even if it's only
once, it could have damaged the inside surface sufficiently for cracking
to begin.
Wow! I think you nailed it, even without the benefit of a good picture.
You are correct that there is no pin for the big ring. It's a Sugino
50 tooth chain ring.
Over the lifetime of the crank, I've dropped the chain maybe 3 or 4
times. When it happened I knew it immediately and was fortunate not to
gouge the crank arm. (Incidentally, with this setup, I've never dropped
the chain while in the small ring.)
No gouges, but there are some surface scratches. Running my fingers
over them, they're not detectable. Perhaps, in hindsight, they really
aren't superficial scratches as you painfully point out.
Couple side notes, the day before the crash I gave the bike a thorough
cleaning (and inspection) after riding through salt and sand ridden
roads. The left crank arm has a small snake-bite indentation which
occurred after hitting the side of a curb while lifting it (and doing so
while off the bike). That happened years ago and I always kept a
watchful eye on that part.
Quoted message said:
again, need better pics of the fracture surface + side-on pics of the
broken arm. inside & outside please.
Ok. Will do. One thing though - I'm missing the other half of the
crank (and the other pedal). I got carted out by EMT and the bike, most
of it, was transported home by a helpful Park Ranger. Follow up calls
to their office were of no help and I'm in no condition to drive. It
would be nice to have the other part available to inspect.
Anyway, I have a feeling your assessment is correct. If so, the truth is
almost as painful as my physical injury. Lesson learned.
More pics are on their way...
