Originally Posted by
gtcuppels
why pinch when its a piston and sleve? Thank you for the answer to my question>
Technically, it's not a "pinch" in the literal sense of the word. The sleeve is placed in a collet-type of device that compresses the diameter, thus "pinching" it down to a smaller size. This is done to restore the mechanical interference that nitro motors need to run properly, since they do not have compression rings.
Pinching a motor is an alternative to purchasing a new one. As long as the sleeve and piston is not scratched, you can pinch an engine 2 or 3 times before needing replacement piston/sleeve. It's a good way to save some cash.