Let's first of all start off with why K'nex motors click. The reason is, if you try to put a motor under too much load for it to handle it will stall and eventually burn out. Obviously this is bad, and the designers of k'nex motors wanted to stop this happening. Or, at least make it so that it is apparent when a motor cannot handle a certain load. They did this by adding the 'clicking' feature. K'nex motors are, obviously, designed to be used with K'nex rods, and so they have to fit the rods. When sliding a rod through a motor's shaft, I'm sure you are aware that you have to push it quite hard to get it to go through. This is because there are two lugs of plastic that stick out and grip in the reccesses of the rods. These plastic lugs are the key to the clicking. When the motor cannot handle the load, the rod jumps round a quarter rotation and the lugs grip another part of the rod.
There is a certain load, under which the lugs do this, and this should be just before the motor would stall. The problem occures when these lugs slip too easily. This means that the motor is not performing at it's best and is being held back, in terms of torque, by these lugs.
This easy to follow, simple & easy instructable will show you how to make these lugs much strong and combat the 'clicking' problem.