The measurement of the squish is done by utilizing a solderwire with a diameter greater than 1,5 mm (ideally about 1,8 mm). This wire is placed inside the combustion chamber, then, by rotating the crankshaft the wire is pressed down to measure the exact minimum distance between the cylinder head and the piston crown.
Going into more details, the optimal procedure for the measurement of the squish provides for the dismantling of the head of the cylinder and inserting a piece of solderwire which length equals the diameter of the cylinder (54 mm, i.e. the cylinder bore). The wireshould be positioned paralleled to the piston rod: in this way, the imperceptible (yet present) play movement deriving from the inclination of the piston which rotates around the piston rod will be avoided.
At this point, the head of the cylinder is reassembled, tightening the screws correctly (one at the time, in a cross pattern with the correct torques) as if the engine had to be reassembled correctly for use.
After that, grabbing the crankshaft by the two sides (spark and sprocket) make it rotate back and forth a couple of times. Then, with a pair of long pliers, extract the solderwire and measure with the caliper the lower part, which is after the “indentation” which formed at the two extremities of the solderwire due to the remaining space between the piston crown and the elastic band.