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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, 06:17 AM
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vintagerando 
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Hair-line cracks in crank arm? Safe to ride?

I was very disappointed to find tiny cracks on the left and right side of the drive-side crank of these Sugino cranks. (If you saw my post in Sales; I am still looking for a Sugino 110bcd crankset)
When i got these cranks, they were covered in grim, grease and dirt.So, I didnt see the cracks. I need some searches on the Web, and it appears the failures tend to happen on the crank arm towards the fluting (pedal end) on these cranks (and similarly on Campy).
So, I understand its difficult to predict if the cracks will get worse. But, I was hoping I could get some opinions of the likelihood (based on personal experience) of the cracks leading to the crank failing.
What are your thoughts?





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Old 06-14-19, 06:31 AM
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Originally Posted by vintagerando View Post
I was very disappointed to find tiny cracks on the left and right side of the drive-side crank of these Sugino cranks. (If you saw my post in Sales; I am still looking for a Sugino 110bcd crankset)
When i got these cranks, they were covered in grim, grease and dirt.So, I didnt see the cracks. I need some searches on the Web, and it appears the failures tend to happen on the crank arm towards the fluting (pedal end) on these cranks (and similarly on Campy).
So, I understand its difficult to predict if the cracks will get worse. But, I was hoping I could get some opinions of the likelihood (based on personal experience) of the cracks leading to the crank failing.
What are your thoughts?
I wouldn't.

Yes, they might be fine for years and years with those cracks. Especially if they are on a bike that you don't ride very hard.

But then there might be that one time where a loose dog starts after you and you stand up out of the saddle and mash to get away, and that's what it takes for the crank to give way.

Just not worth it, imo. A crank failure would likely happen when you are putting out a lot of power, and crank failures are up there with sudden fork failure or shearing a pedal spindle in levels of severity and danger, and likely injury to yourself.
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Old 06-14-19, 06:39 AM
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I broke a crank arm about 12 months back and I didnít get any warning signs. While it scared the hell out of me, it didnít put me in any immediate danger, but you never know when itís going to give way, so I say - bin it.
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Old 06-14-19, 06:44 AM
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Cracks almost invariable propagate and lead to catastrophic failure.
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Old 06-14-19, 07:05 AM
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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.


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Old 06-14-19, 07:18 AM
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What would Murphy say ?
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Old 06-14-19, 08:09 AM
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Balance an awkward fall where you break a collar bone, wrist, arm, damage a knee, against the cost of replacing a set of crank arms, it just isn't worth the risk. While it sucks to replace crank arms it's also great that you can see the crack and know the condition exist. Also Sugino cranks are pretty plentiful.
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Old 06-14-19, 08:17 AM
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-> scrap bin or wall hanger material now, sadly. Aluinum is very delicate about notch effect and will give up without prior notice. Doesn't take a lot of phantasy to picture the effect of a crank breaking while riding standing, as, for example, pulling away after a top.
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Old 06-14-19, 08:24 AM
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I would not ride that crank. I really like the idea of turning it into a bottle opener as suggested by @gugie! FWIW, you can reduce the likelihood of developing these stress cracks with some preemptive filing/sanding of the sharp edges. I've done this to several Campy & Sugino cranks that I have....barely noticeable if done with care. Sadly, I view yours as too far gone for this treatment.

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Old 06-14-19, 08:27 AM
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Originally Posted by T-Mar View Post
Cracks almost invariable propagate and lead to catastrophic failure.
Which is very true. Cracks spread and propagate. Failure is on it's way. And especially if you have to pedal hard and fast to escape some dog, or keep up with the peloton. I'd just hunt down a replacement, service the bike, and then go back to knowing you're good and reliable.
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Old 06-14-19, 08:30 AM
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While I see a lot of posts on frames where people are going overboard on things not being safe .. this is one that I would recommend not riding. There will be no warning and if you are putting any serious force on it .. it could be a serious injury.
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Old 06-14-19, 08:31 AM
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I've retired a couple of cranks with cracks similar to those. One heavier rider I know here crashed a few years ago as he stood to accelerate and the crank arm broke. He ended up with a concussion and broken ribs. I've inspected my older cranksets more frequently since then.
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Old 06-14-19, 08:32 AM
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I hit the road really hard a few years ago when my Sugino Mighty Tour crank broke. That crank should go to the metal recyclers. Don't risk injury.
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Old 06-14-19, 08:33 AM
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I consider myself to be the guy who says "nah, ride it!" in marginal situations. In this case I would not.
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Old 06-14-19, 08:36 AM
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Medical bills are more expensive than a replacement crankset and effort to install.

Love the bottle opener idea!
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Old 06-14-19, 09:00 AM
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Been there ... done that -- snapped a Sugino Mighty Compe crank across the pedal eye during an out-of-saddle climb. I was not too seriously injured in the resulting fall, but certainly could have been.

I have broken frames at the bottom bracket shell and the drive side chainstay, even the front of the downtube, with no threat to my well-being, but I do not trust handlebars, stems, cranks, chains, steerer tubes, or forks.
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Old 06-14-19, 09:30 AM
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That crack is pretty far in. I'd expect it to crack any day. Not safe.

When cracks first appear in this location, you can typically continue to ride for a little while, but this one has been going a while already. Time to recycle.
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Old 06-14-19, 09:44 AM
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I too would err on the side of too high a risk. However, the first picture looks like a void as does the second but with the addition of propagation. Curious locations! I would expect them to be nearer the arm/spider junction.
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Old 06-14-19, 10:04 AM
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Wouldn't even consider it. I broke a crank once just after a relatively steep ascent when the trail had become less severe. No problem since I was pedaling easily; really glad it didn't occur on the steep part.
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Old 06-14-19, 10:04 AM
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I've never seen a crank crack or break there. Across the pedal threads is common and across the taper flats happens. That said, cranks break unless retired before they do. That crack will grow. Perhaps (and I am thinking unlikely) the crack will grow across the spider web and not be catastrophic. I think the crack progressing slower into the crank itself is more likely.

The three crank failures I have seen first hand were two Campagnolo cranks tha tbroke on bikes whose wheels I was on in races and myself. Both Campy riders crashed. I did well to slip past. First starting a climb when he came out of the saddle. Second coming out of a downhill criterium corner. Mine was as I stood for the last few feet of a minor climb. Put my foot down on the road, sat down, stopped, dismounted and clomped around looking for my pedal until I realized it was on my foot! I had 3/4s of a mile of downhill to meet friends. One had a pickup. Sometimes you get lucky.

So, as I said above, cranks break unless retired before they do. This one is asking for that retirement package.

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Old 06-14-19, 10:18 AM
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Interesting to see a crack (if it is one) inside the spider arm instead of where it meets the crankarm, where you would expect it. Can you see the crack on the backside at all?

Since the consensus is that the crank is toast, you have nothing to lose by getting out the Dremel and seeing how far you can go in with a skinny grinding stone. Some of the pictures make it look like no more than a weird scratch.
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Old 06-14-19, 10:51 AM
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Originally Posted by ThermionicScott View Post
Interesting to see a crack (if it is one) inside the spider arm instead of where it meets the arm, where you would expect it. Can you see the crack on the backside at all?

Since the consensus is that the crank is toast, you have nothing to lose by getting out the Dremel and seeing how far you can go in with a skinny grinding stone. Some of the pictures make it look like no more than a weird scratch.
No "crack" does not go the backside (I should have mentioned that). It can barely even be felt on the front with the tip of your finger.
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Old 06-14-19, 10:59 AM
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Thats a really odd spot for a crack that was caused by heavy pedal smashing, or rider weight.

Looks like a crack in the casting process and it could possibly be merely cosmetic.The aluminmu probably developed fatigue over the years and the crack eventually showed up ,For it to be on the Drive side on that braced/supported area is very rare ,usually the cracks develop on the square taper on the outermost corner. In that case its Junk.

If you have a Tig welder available you can bevel cut it to see the depth of the crack , lay down a bead,polish it back up and you'd be ok.
All this depends on the severity of the crack.

Crank arms usually do not develop cracks there, it could be a fluke.
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Old 06-14-19, 07:20 PM
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Originally Posted by ThermionicScott View Post
Interesting to see a crack (if it is one) inside the spider arm instead of where it meets the crankarm, where you would expect it. Can you see the crack on the backside at all?

Since the consensus is that the crank is toast, you have nothing to lose by getting out the Dremel and seeing how far you can go in with a skinny grinding stone. Some of the pictures make it look like no more than a weird scratch.
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?
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Old 06-14-19, 07:27 PM
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Originally Posted by Manny66 View Post
Thats a really odd spot for a crack that was caused by heavy pedal smashing, or rider weight.


Crank arms usually do not develop cracks there, it could be a fluke.
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.
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