Iame designates their piston sizes by bore size, not the actual size of the piston. The marked size on the piston is based on Iame’s recommended piston/cylinder clearance for the Swift (which is .09 mm or .0035"). For example, a piston marked 41.80 is actually 41.71mm in size, measured at 15mm from the bottom of the piston. In other words, if you measure a freshly honed cylinder and it measures 41.80mm, Iame recommends the piston marked 41.80 so you will wind up with the factory recommended clearance of .09mm. Also confusing, is that for any given piston size, Iame makes a "green (V)” size, and a "red (R) size”. The green piston is .09mm smaller than the marked size, while the red piston is a bit larger at .08 smaller than the marked size. This allows a very precise range of sizes so you can always get to your target clearance. Please bear in mind, the factory clearance is for an emphasis on longer rebuild intervals, not maximum performance. You will find builders normally build with a fair amount more clearance than .09mm. The following table lists all of Iame's Swift pistons with their marked size and actual size (both green and red) listed. This table makes it a bit easier to pick a given piston based on your bore size and your intended cylinder clearance.

MARKED GREEN V RED R

41.80 41.71 41.72

41.82 41.73 41.74

41.84 41.75 41.76

41.88 41.79 41.80

41.92 41.83 41.84

41.96 41.87 41.88

42.00 41.91 41.92

42.08 41.99 42.00