Rating A? Rating B? Rating C??? Are you a little lost when you have to choose the size of your piston? Well in this 3AS tutorial, the Doc explains how to measure the diameter of your piston and cylinder to respect the famous functional clearance between the cylinder and the piston, here we go! First of all, you must understand that a piston must be able to operate freely in your cylinder. After several hours of driving, the cylinder wears out and so does the piston. You may lose compression and therefore power. Changing your piston is essential while respecting the wear of your cylinder to adapt the correct dimension of the piston A, B or C. The functional clearance between the piston and the cylinder must be 0.05mm. To determine the correct dimension of your piston, here is what you need: A pair of glasses (if you need them of course). The DRAPER metrology kit with the palmer and the bore checker. Let's move on to the measurement, here are the steps: Step 1: Measure the diameter of your piston using a palmer/Micrometers. We keep a measurement at 77.45mm Step 2: Report the dimension of your piston in the cylinder using the bore checker. We keep a functional clearance of 0.09 or a cylinder with a diameter of 77.54mm Step 3: Compare the 2 dimensions to calculate the new dimension of the piston. A correct functional clearance must be 0.05mm. We have too much clearance of 0.09mm. We therefore have 0.04mm of excess clearance. Therefore the new piston will have to measure 77.49mm Calculation detail: 77.54mm (piston dimension) + 0.04mm = 77.49mm Step 4: Order your new piston with the dimension of 77.49mm. You have all the cards in hand to order the piston that will fit your motorcycle. The measurement cannot be done via a caliper, it is not fair. You can invest in the bore checker to measure only your cylinder and therefore subtract the famous 0.05 to find the correct piston dimension. Good calculation and measurement to all! #TutoMoto #3ASRacing 3as racing, the largest selection of motorcycle parts https://www.3as-racing.com/ Subscribe: / @3as-racing Our FB: / 3asracing Our Instagram: / 3as_racing Video presented by: Docteur Biclou And Simon Peterolff from @SIMONSGARAGE Youtube: / simonsgarage ​Directed by @MartinPeterolff and produced by @Khulan-agency ​http://www.khulan-agency.com/​​ 3as racing, the largest selection of motorcycle parts https://www.3as-racing.com/ Subscribe: / @3as-racing Our FB: / 3asracing Our Instagram: / 3as_racing