What you'll need: Cylinder Bore Gauge Digital Micrometer Pen Paper Calculator You'll use the bore gauge to find the width of the cylinder as shown in the picture. Make sure the bore gauge is level then tighten the lock. You will measure 3 spots; Top being (x), Middle being (y), & Bottom being (z) of the cylinder. Each spot will be measured in 3 different angles. Each color represents a different angle Red being (1), Blue being (2), Yellow being (3). After you have tightened the bore gauge use the digital micrometer to measure the bore gauge. Its good practice to zero out the micrometer before measuring. Make sure to write down each measurement. For example my measurements are: X1 - 66.39mm X2 - 66.45mm X3 - 66.46mm Y1 - 66.38mm Y2 - 66.48mm Y3 - 66.43mm Z1 - 66.47mm Z2 - 66.42mm Z3 - 66.46mm The reason you have measured the bore in 3 spots at 3 different angles is (a) to get the average bore size and (b) to find the cylinder taper. The math to find your average bore size of each "spot" is: X1+X2+X3= 199.3 ÷ 3 (the # of times you measured the "spot") = 66.43mm 66.43mm will be my average for the (x) measurements. You can then do the math of each "spot" average to get an overall bore size. (x average) + (y average) + (z average) = 199.31 ÷ 3 = 66.44mm The Blasters stock bore is 66mm. As you can see my cylinder is worn out pretty good, and i will need to have it bored out to 66.5mm. Here is a chart to figure out what your next bore size will be and what piston/rings to purchase. 66.0mm - .000 bored over 66.5mm - .020 bored over 67.0mm - .040 bored over 67.5mm - .060 bored over I am not a professional engine builder or a master mechanic so if there is any wrong information here please let me know and i will correct it immediately.