Loose Cotterless Crank

Left cotterless crank on the titan 36er came loose on a ride. Bought a long allen key but could’t get it tight enough until I used it like a crank and stepped on it at which point it levered out sideways. Hoping it holds to a train station though its a nice day for a walk.

Can I get a crank bolt at a bike shop or are they unicycle specific?

Not sure that will be enough, but this one is clearly munged so will need at least that.

So far all the ones I’ve seen were M8x1.0, same for both, but check and see. I bought a nut at the hardware store for about a quarter, either it threads or it doesn’t. Measuring is more of a pain as the years go by and the eyes get more tired.

Give it some blue Loctite and torque to spec and see. Good luck!

Don’t ride it if there’s any slop in the crank/spindle interface or you’ll ruin the cranks. Wait until you can get it right. The bolts (or nuts on some setups) are standard, so a bike shop should have them. Probably worth taking your old bolt in to confirm the length.

Fortunately it seems the final field expedient tightening got it somewhere close to where it should be, so I was able to ride back to the subway without more wobbling.

The existing bolt is damaged enough that getting it out may be hard; I don’t dare tighten it any more because of that.

The big question will indeed be if tightening a new bolt will be enough, or if I need to replace the hub or cranks. They are venture aluminum ones, so the whole aluminum broaching itself wobbling on steel though was very much on my mind was I was trying to find a way to tighten them.

Had taken the commuter train north from NYC to where they close the Bronx River Parkway on some Sunday mornings for recreation. Almost immediately felt something was wrong but assumed it was a pedal that had developed end play. Pulled into their cycling advocacy “rest area” and was asking a guy from a bike shop about pedal end play when I felt the crank move in my hand. He tightened the bolt with a large multi tool, though I was soon to learn how drastically insufficient that torque was.

The crank soon started wobbling again, and I assumed there would be more assistance at the north end of the event, but there wasn’t - however while asking around for tools, I met a “once and future” unicyclist who was there on two wheels. He offered to drive me to home depot; though first we stopped by his garage to unload his bike and check out the brand new Nimbus 26er he just bought and is looking for a place to re-learn on, decades after some unicycle basketball experience.

Home depot allen key in pack, I was dropped off at the North Country Trailway that all but ran behind it and explored that a bit before deciding that the continually re-loosening bolt was not a solved problem. I did my standing on the wrench bit, and turned south for home - both munging the bolt, but apparently getting it tight enough that there was hopefully no more crank damage on the ride home. Even did pretty well on the dirt trail in Van Cortland park until I lost it in the gravel trap - my first failed UPD on the 36er, but only a few bruises.

So now I’m sitting at my kitchen table recovering and shopping for crank bolts.

In my experience once the flats on the crank start to get rounded it is a never ending battle to keep the crank tight. Unfortunately, it sounds like you might be looking for a new crank arm. At least you can rest easy knowing that the crank is the only thing wearing out.

Hopefully you can get it tight enough that you don’t have any problems.

In my experience once your cotterless crank has wobbled, tightening the bolt alone won’t seat it properly and avoid future crank interface degradation.

This is where a mallet comes in. I would install and tighten the crank like normal, then give it a few whacks over the bolt hole, then re-tighten the bolt on BOTH sides.

If it works, you just saved yourself the cost of a new set of cranks, If it didn’t then the cranks were wrecked anyway and no harm done. I would avoid taking off the cranks after giving it the mallet treatment, as I am sure you can only do it so many times.

Even worrying just about the bolts for the moment, it’s a bit confusing.

I actually took the bolt all the way out before the final tightening that damaged it, and my memory is of a very near visual match for the bolts sold for ISIS drive hubs - ie, a “socket head cap screw” with a very wide flange. But this is a square taper cotterless hub, so I presume the thread must be smaller.

In contrast, the bolts pictured for UDC cottlerless hubs and sold as replacements are ordinary external hex head bolts, not socket head.

Ultimately the means of tightening the bolt doesn’t matter to it’s compatibility to the unicycle, but it’s odd that what I have doesn’t seem to be supposed to exist.

Edit: a little searching and it seems UDC UK has them, and markets them as avoiding the need to carry a socket; so perhaps they really are intended to be interchangeable. I’d almost rather have the external hex, as getting enough torque on it without damage seams easier.

Maybe he used to ride with the King Charles Troupe; not necessarily the actual performers but the neighborhood group(s) from which they came.

Lay the wheel on its side, and either take the pedals off, or find something to put under the crank that’s on the bottom. That’s how we used to install cotterless cranks all the time, back in the day. We would pound them first, tighten, then pound again and tighten. Worked for steel and aluminum both. I’m still using some Miyata cranks from the early 1980s. As long as you don’t damage the threads, they seem to hold up pretty well. It’s only a problem if they were ridden while significantly loose. Some people are more sensitive to loose cranks than others (it’s an acquired sense); if they were only moving slightly, the damage may be very minor.

I agree. I’m not a fan of pedals that require a hex wrench, and I haven’t had any cotterless setups that have that. Almost all of mine are older, which means they have a nut, which goes onto a threaded spindle on the end of the axle. I think the bolt design is stronger, but it was normal for me to carry a pedal/crank wrench on ride, especially if it was a group. But that faded away, until hardly anybody was riding cotterless on dirt anymore. I still carried it when I rode my old Coker, but mostly stopped riding that one when I got my KH/Schlumpf in 2010.

My advice: If you do long rides with cotterless cranks, bring along the necessary wrench. You might not need it on the ride, but it’ll be there if/when you do. I would always give both sides a tighten before starting the ride, and that was usually all that was ever needed.

I’m old enough to remember when external hex crank bolts were the normal kind:

Yes, that seems to be the future. Would love to figure out a setup where I carry one lever bar and various sockets/bits etc. Almost tempting to rig up something to turn the seatpost into a 1/2" drive non-ratchet wrench handle, with a thin pedal flats crow foot, too. Or figure out a bar that can be carried in the seat tube, or under the saddle - adding a 13 piece extra long hex key set to my backpack was noticeable, the foot long breaker bar I considered buying instead actually weighed less.

I think I’m going to see if I can scare up an external-hex-head bolt for the cotterless cranks locally, research last night suggests they’re pretty normal and standard except perhaps for the length, so will see if I can get the munged one out (hopefully without unseating the crank from the taper, now that it’s finally somewhat secure). I think that near full revolution of tightening from what I could do by hand, accomplished by stepping on it twice may have closed up the wiggle. Could easily have been a few hundred pound inches of torque applied.

The whole episode did re-ignite my questioning of cotterless setups, particularly for big wheels - ie the irony of owning a splined 26er and a cotterless 36er. Spent a bit of the ride imagining ordering an ISIS drive hub and re-building the wheel, then perhaps re-using the old hub to build up a Kent 32" wheel and leave at relatives as my nephew starts to get ready to discover bike paths, or buying an entirely new unicycle, or whatever.

Personally I don’t mind pedals with hex sockets, as long as they also have wrench flats, as I can remove the pedals with a wrench at home but then install them at a riding location with just a multi-tool, of course that assumes I’m riding all the way home or at least to transit where having the pedals on is known to be okay. My guess though is that removing the pedal with a foot long crescent wrench, with the crank bolt already (but undiscovered loose) is what set off the whole incident.

Didn’t specifically ask, but indeed possible. Have been stopped for conversations by least two others with what sounded like that unicycle background in rides around the city.

Lots of shouted appreciation in the Bronx on the way to/from Van Cortlandt park, too - most of it I think more original than based on any local history.

Hex bit for the socket wrench that I bought a while back since it’s the same 8mm needed for a splined uni turned out to be a far more secure fit than the long hex key was, so removing the old bolt with a socket wrench was no problem.

A five minute walk to the local bike shop and $3 spent resulted in what appears to be a close enough internal-hex replacement; may still try to source the external hex variety, but at least I have something with an undamaged hex socket that I can tighten in there without fear of being unable to get it back out, if I don’t find something I like better by the time I’m feeling recovered enough to ride (in essence the reason I started this thread even before I finished the ride in question was to figure out if I needed to be ordering a unicycle-specific replacement part first thing this morning).

Bike shop counter guy argued for tapping the crank on rather than trying to draw it on with the bolt. May try a bit more of that as I install this, though probably with a piece of wood on the opposite side and relying on inertia rather than against a solid “anvil” (I did briefly consider using a C clamp through the spokes, but could see that going wrong and don’t have one at hand anyway).

Guess I probably should have opted for the socket wrench hex bit and breaker bar to start with. Since I already had the bit at home, what I need to do is find a suitable wrench to carry. Surely someone makes a titanium non-ratcheting socket wrench handle. (And surely it’s more than I’d want to pay)