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Hair-line cracks in crank arm? Safe to ride?

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Hair-line cracks in crank arm? Safe to ride?

Old 06-14-19, 07:29 PM
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Originally Posted by sdn40 View Post
What would Murphy say ?
He'd say....."Have a Guinness my friend"
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Old 06-14-19, 07:45 PM
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This situation reminds me of this morning as I got in my old Lincoln to drive to our club's Fast Fridays ride.
I went to start the car, but it would only crank, no sign of fuel+spark!

So the ride was nixed, I did some diagnostics and prepared to replace my Crankshaft position sensor, a 1-2 hour job.

When I was under the car with the shield off, I first removed the wire connector before removing bolts to move the AC compressor out of the way.
I then thought to jiggle and remove/reinstall the connector then try to start the car, ...and it started!

But it gnawed at me to think if this possibly-intermittent sensor quits again while I am out of town, ...I wouldn't sleep thinking about it!

So I rode my bike to the auto parts store, bought the $30 sensor and went to work.

I can't express how HAPPY I am that this occurred in my driveway, ...and not somewhere else.

Get the point?
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Old 06-14-19, 08:54 PM
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Originally Posted by vintagerando View Post
Yes, my research on the Web (and some posters here) indicate that the Mighty breaks at the end of the fluting design near the pedal. It really looks like its on the surface.

In addition....the original owner (and only owner) is a guy of slight build. Maybe he had a different build years ago, but this fellas is several inches smaller than me. His son was there when I bought the bike. Again, his son (probably in his mid 30s, is not a big guy; maybe 165lbs and 5'9-10". The origjnal owner was a recreational rider; i just think he never used this bike hard.
FWIW I broke or cracked at least 2 or 3 cranks when I was a 155 lb junior. Big doesn't necessarily matter. It happens. I did ride a lot of miles.

Cranks can break at or near the pedal eye, in the middle of the shaft, or at the spider like this one. They will eventually break from a crack at the spider, but it takes longer. As I said, this one is far along; it could break at any time.
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Old 06-14-19, 10:38 PM
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Originally Posted by vintagerando View Post
You have my attention. Take me to school. (I do have a Dremel with 50 accessories). So, what is the approach. Grind out the anomaly?
Some folks used to use rat-tail files to smooth the sharp edges between the crank arm and spider to try to prevent cracks. If it were my crank, I'd just try grinding through it, see how deep it goes.

Bummer that yours probably isn't trustworthy. I've got a Sugino GT, and I've long lusted for the lighter, sexier Mighty Tour.
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There's no such thing as too far.. just lack of time
Originally Posted by noglider
People in this forum are not typical.
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Old 06-15-19, 06:34 AM
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Originally Posted by sdn40 View Post
What would Murphy say ?
Murphy is the guy who wakes up on his head because his Murphy Bed folded up while he was sleeping.
"Far and away the best prize that life offers is the chance to work hard at work worth doing." --Theodore Roosevelt
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Old 06-15-19, 07:50 AM
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the story of Murphy's law was that he caused a batch of failures by not considering what might go wrong. They named the law after him.

Campagnolo cranks crack at the intersection of the spider and the crank arm. People grind those cracks out. There is plenty of material, they crack because the interface is too sharp. This looks too big to safely remove. You can try it, I suppose. It certainly looks like a fatigue crack that has propagated quite far. It's really hard to remove all of a crack. It gets pretty small at the crack tip and the material is pressed together by the plastic zone. You might be able to see it under magnification, not sure.
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Old 06-15-19, 05:25 PM
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Originally Posted by gugie View Post
With aluminum, there's no way to know. I sadly had to chuck a set of Stronglight 99 crankarms for the same reason.

Hackoff all the spider arms, file and polish, cut out a bit of the pedal area and make a bottle opener out of it.

The possibility of a catastrophic failure of the bottle opener is something to keep in mind, though.

"Progress might have been all right once, but it has gone on too long."
--Ogden Nash
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