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In the days before very high strength alloy materials, pedals were held in place with cotter pins.

This system takes best advantage of slightly softer materials, and may even be more dependable than modern splined systems. Cotter pin systems give plenty of warning before failure and can be tightened up and fixed several times. However, this natural reliability does not conceal the fact they need a lot more maintenance.


Function

The cotter pin is wedge shaped, with a threaded stem and a nut that pulled them into a wedge-shaped hole. Cotter pins should always be used so that the widest part takes the pressure of the pedal (the thinner and threaded end doesn't actually squeeze tight into the hole, so is unable to take this pressure).

Cotter pins that have been correctly fitted last a long time and, when they do start to wear, will normally be found to have corroded into place in their hole. In which case they can be quite difficult to remove. Loosen the nut a single turn before applying a hammer and hitting it. That way, the damaged portion of the thread will be recovered by the action of further undoing the nut - remember, these parts are all soft and deform when you hammer them. However, in many cases, this precaution gains little, the pin is damaged and you will need a new pin (which of course you will have handy). Properly equipped workshops remove stuck cotter pins by heating the pedal crank, a procedure that releases most stuck items.

Trivia

The correct use of cotter pins, described above, causes both cotter pins to point in the same direction (ie both pin heads or both nuts point at the ground). So the pedals are slightly out of line, and one leg pedals slightly ahead of the other. Cycle chain wheels are always on the right (unlike motorcycles, which can be either side) to take advantage of this effect and use the stronger right leg for more than 50% of the time.

However, this effect may not be noticeable to you, since the later, more advanced production facilities machined the notches in the crank-pin slightly out of line, making this effect near invisible.

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