Here are some instructions how to change cranks over on your unicycle. There are four types of cranks commonly found on unicycles: cotterless, ISIS, splined and cotter-pinned.
This is the standard crank that comes on most modern unicycles. The hub axle has tapered ends with a square cross-section and a bolt or nut to hold the cranks on. The cranks are forced onto the axle to create a friction fit and locked in place with the bolt or nut. You should never ride with loose cotterless cranks as this will round the corners off the axle and distort the square hole in the crank, preventing them from fitting tightly ever again. To remove cotterless cranks you will need a crank extractor. First remove dustcover (if fitted) then unscrew and remove (anti-clockwise) nut/bolt with 14 socket spanner or 8mm allen key. Retract the central shaft of the crank extractor fully before screwing the outer clockwise into the crank fully. Next turn the shaft to extract crank. Then unscrew the outer threaded section to separate it from the crank. To fit cotterless cranks; gently seat the crank on the axle stub then tightly lock in place with the bolt/nut. Make sure the righthand crank is on the righthand side and the lefthand crank is on the lefthand side before riding otherwise you will wreck the cranks.
This is now the standard (2019) for the strongest hub crank interface and is used on all different types of unicycles from Freestyle to Trials and Road. These are a type of splined crank but have tapered axles so their removal is similar to cotterless cranks BUT you must use a crank extractor with an ISIS head otherwise it will damage the threads in the axle. Some extractors have a removable ISIS head so you can use them on cotterless and ISIS cranks. The ISIS head has larger diameter than the cotterless version.
Splined cranks are used a lot less than they used to be and as such Qu-Ax are the only company using this technology at this time (2019). They are stronger than cotterless cranks and therefore are more suitable for muni or trials unicycling, but require slightly more maintenance. There are several different models; Onza, Kris Holm, Profile, Qu-ax, Koxx, Onza/Kris Holm, Qu-ax ISIS, Onza ISIS, Nimbus ISIS and Kris Holm ISIS. With the exception of the Onza with the Kris Holm/Onza cranks and all the ISIS cranks with each other (not Koxx), these cranks are not cross-compatible as they fit different spline formations. The bolts will probably need to be tightened after a week of riding and checked regularly after that. For more information read our section on maintenance of splined cranks. Never ride with the cranks on the wrong side or you will destroy them.
These do not come on any new unicycles The crank is held in place by a tapered bolt, called a cotter-pin, which is at right-angles to both the axle and the crank. To remove the cotter-pin; unscrew the nut slightly then carefully hit with a hammer/mallet. Repeat this process until the pin is completely removed. Do not completely remove the nut and hit it with a hammer since this tends to bend the pin, making complete removal a little more difficult. When you change a cotter-pinned crank it is recommended that you also replace the cotter-pin. Before riding, make sure the righthand crank is on the righthand side and the lefthand crank is on the lefthand side before riding otherwise you will ruin the cranks.