Bicycles/Maintenance and Repair/Cranks
Types of Cranks 
Cranks come in various forms.
One piece 
In one piece cranksets, there is a single piece of metal bent into a Z shape that forms both cranks and the bottom bracket spindle. These types of cranks are usually found on lower end bikes and BMX bikes. The bottom bracket shell on one piece cranks is much larger than other for other bottom brackets.
Cottered Cranks 
Cottered cranks are decidedly the older standard, but replacement parts are still available. Cottered cranks are held with a cotter pin to the bottom bracket spindle. Common repairs on cotter cranks involve the replacement or refacing of the cotter pins which often become worn over time, leading to slop in the cranks. For proper alignment the cotter pins on opposite sides of the bicycle must be pointed in opposite directions, otherwise the cranks will not be 180 degrees apart.
Cotterless cranks come in two main types:
Square Taper 
Square taper cranks have a square taper in the mounting hole. The crank is held on primarily with friction, and fixed in place with a crank bolt or nut (depending on the type of bottom bracket).
Splined cranks use a multi-toothed spline to hold the crank. These come in various standards including ISIS and Shimano Octalink (V1 and V2). ISIS is an open standard that has been adopted by various manufacturers in response to the proprietary Shimano standard.
Hollowtech II 
Two piece cranks where the drive side has a shaft bolted on which is then pushed through the frame (and bottom bracket)then non drive side attached. Bottom brackets for Hollowtech II are external and require a special tool to remove. Removal of cranks and bottom bracket with Hollowtech II takes around 2 minutes, because of this it does not require much bicycle knowledge.
Crank Removal 
- Cotter pin removal
- Crank bolt/nut removal
- Crank puller
- Hollowtech II removal tool.
- (details need to be completed)
Removal of Seized Cranks 
It is common for cranks to be come seized (by corrosion) to the bottom bracket spindle. The removal of seized cranks is time intensive and can damage the cranks, the bottom bracket bearings and the frame, so caution is advised. Household ammonia can be used to dissolve corrosion between aluminum and steel. (details need to be completed) If bottom bracket is damaged it will need to be "Faced and Chased" at your local bike shop.
Crank Installation 
While somewhat debatable, grease is generally recommended when installing cranks. The removal of seized cranks is time intensive and can damage the cranks, the bottom bracket bearings and the frame. (details need to be completed)