stroke

[Eddiesanders250]

what exactly is stroking the crank??

[2muchquad]

machining of the crank for more stroke or "throw" which increases displacement:D

[wilkin250r]

Have you ever seen a crank, either in person or just a picture? Look at how it's structured, and imagine it in motion. The stroke of the piston (how far it travels up and down) is determined by how far the connecting rod is located from the center of the crank.

To "stroke" a crank, you actually machine the crank to move the connecting rod even further out from the center of the crank. To achieve a 4mm stroker, you move the crank out 2mm further away from center.

It requires not only very precise machining, but also a whole wealth of knowledge that the changes will produce. You usually end up with a different length connecting rod, and if you have a 2-stroke, you radically change the port timing. All that needs to be taken into account.