MX | ROADRACE | KARTING | MOPED
Here we explain how to measure the piston to cylinder clearance. It's very important to measure the cylinder bore, as it could deviate from the standard expected bore size. When mounting a piston, you need to make sure there's a certain piston to cylinder clearance. We indicate this on the packing list, included with each VHM piston.
You'll need a cylinder bore gauge (including dial indicator) and a micrometer.
Place a cylinder bore gauge (including dial indicator) in the cylinder. Move the gauge from left to right to see what the maximum runout (altitude) shows on the dial indicator.
Set the big pointer from the dial indicator to zero at the maximum runout.
Click on the pictures to enlarge them.
When you know the exact cylinder bore size, you can check what piston diameter you need. With all VHM pistons, a packing list is included in the box. The minimum piston to cylinder clearance is indicated on this list.
For example: your cylinder bore is Ø54.02 mm and the minimum piston to cylinder clearance is 0.07 mm. Then you should need a piston diameter of Ø53.95 mm.