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I have a FSA Crankset which is missing a crank bolt. The crankset is CK-C6028 from ca 2016.

I was recommended by FSA to buy this: https://www.fsaproshop.com/products/alloy-nbd-bolt-assembly-black

I was wondering if it is dangerous to ride the bike without this bolt. And when I receive it, do I need to just screw the bolt in?

How was the bolt removed and the crank arm is still in place?

Crank

Crank model

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    "How was the bolt removed and the crank arm is still in place?" Mostly by luck. It is not supposed to really hold together without the bolt, some remaining forces hold it. I certainly would not continue riding it as is. But as I do not know the details of this system, I will not answer about the fix. Sep 1, 2023 at 8:47
  • Where does that QR code take you?
    – Paul H
    Sep 1, 2023 at 15:15
  • @PaulH thQR code probably contains just the serial number in machine-readable form, for stock management.
    – Criggie
    Sep 1, 2023 at 22:12
  • @PaulH the QR code was not scannable, perhaps due to wear
    – Rookieman
    Sep 2, 2023 at 7:54

3 Answers 3

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First and foremost, stop riding immediately. The crank arm could fly off entirely and you will crash if and when it does. Additionally, the bottom bracket bearings could lose preload and wear prematurely. Buy and replace the bolt.

FSA cranksets have the spindle pressed into the drive side crank arm. While the photo you provide is very low quality, I believe nothing but friction is holding the crank arm on at the moment. It's not uncommon for crank arms to get a bit stuck on the spindle and require the use of a mallet to remove, so that's why the crank arm is still in place.

Bolts loosen. Bolts on the left side of your bike loosen more. That is why pedals and (non-ITA) bottom brackets are threaded in reverse on the left side. When you get a replacement, make sure it has threadlocking compound applied to the threads (looks like a dry blue paste) or apply it yourself. Make sure to use low-strength, blue compound, or it will take a blowtorch to remove the crankset in the future. It's best that you use a torque wrench to install it to specified torque, which should be stated on the bolt or crank arm, or go to a bike shop to install it.

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  • It looks like the bolt usually comes with the threadlocker pre-applied. At least in the photo in the link from the question. Sep 1, 2023 at 8:53
  • I’ve done this once, because I had lost the bolt and I didn’t know better. The crank did not fly off. The failure mode is probably not dangerous. You’re forgiven for not knowing since few people are silly enough to put themselves in that situation.
    – Weiwen Ng
    Sep 1, 2023 at 21:16
  • It’s not just preferable that this is torqued down correctly, it’s important for safety so that the crank arm doesn’t randomly come loose, and that means this should absolutely be done with a proper torque wrench, not some estimate or jury-rigged measurement tool. Sep 1, 2023 at 21:34
  • @WeiwenNg was that a square taper or hollow spindle crankset? For the former, it’s not that dangerous indeed. Hollow spindle cranksets - maybe some press on real hard and would stay on. My Easton crank arm falls off by itself when I undo the pinch bolt, I wouldn’t make it 50 meters before it was no longer attached.
    – oscu0
    Sep 2, 2023 at 8:54
  • @AustinHemmelgarn sure, but it’s a gigantic bolt, you could just get it as tight as possible and it’s probably be fine. The stupid wave washer FSA uses for preload complicates things, though.
    – oscu0
    Sep 2, 2023 at 8:55
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The crank arm could have been put back on after the bolt was removed. That's most likely with a self-extracting crank, though removal of the whole crank bolt assembly is possible. Then it was probably lost.

I'd remove the crank to fit the new bolt assembly, if I could. That would be the best way to ensure it goes fully into the crank without stressing the threads. But you might have trouble getting the crank arm off (try putting a piece of wood against the inside of the crank, and hitting it).

I wouldn't ride on it. Apart from the risk of the crank arm suddenly coming off and causing a crash, there's also a much larger chance of it getting damaged.

If it was the only way to get home (via the nearest train station) or to a bike shop, I'd ride very gently, avoid traffic and rough surfaces, and not clip in to the pedals. Any hills should be walked up and descended with your weight on the good side. This is all to reduce the chances of it failing under load (particularly bad if you're standing on the pedals), at speed, or when a wobble would put you in a dangerous situation. In gentle riding a crank or pedal falling off isn't particularly dangerous.

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You must not ride it with the crank bolt missing.

The crank is held on to the spindle with a press fit. The crank bolt is what initially presses it on and also acts as security against the crank working off the press interface in use. As you've noticed, the design has some capability to hold for a while with the bolt gone. However, it can't do so reliably. The crank will fall off eventually in use without the bolt in place, which is very dangerous. It will likely happen at a high power output moment, which makes it easy to lose balance and fall. The crank splines will likely also be ruined at that point. You're lucky this hasn't already happened.

When you have the new bolt, grease the threads, the shoulder, and the contact surfaces with the extraction cap (the outer piece with the pin holes). Leave the extraction cap threads dry and loctited. Torque it to its printed 41Nm, or if you don't have a torque wrench then use a long-handled tool and tighten it hard. Secure the extraction cap with an appropriate pin spanner. If you improvise something, make sure it's something that can actually get reasonable torque on it, i.e. not a pair of needlenose pliers in the "X" position. Re-torque the crank bolt after a bit of riding.

There is some consideration to pulling the left crank completely so you can inspect the condition of the crank splines. That the crank is still on the spindle implies that the splines are probably fine, but they get destroyed quickly if ridden loose so I would recommend checking them out of caution. To remove the crank, all you do is install the crank bolt and extraction cap as above, then unscrew the bolt. When you reinstall it, clean and grease the splines and the taper interface on the spindle and crank.

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