01 / Squish clearance, or simply squish. Squish clearance is the distance between the piston and the cylinder head edge when the piston is at top dead center (TDC). If this distance is not adjusted correctly, strong detonations can occur, which in turn can cause the piston pin bearing to break and destroy the engine. Therefore, you should not neglect adjusting squish under any circumstances.
To measure squish, we use simple solder with a diameter of 1 mm, which you can buy at any hardware store.
02 / Make a 90° bend, with about 2 cm to the end.
03 / Mount the cylinder without base gaskets and spacers, then insert the wire into the spark plug hole with the piston at bottom dead center (TDC).
04 / Turn the crankshaft by hand. As soon as the piston is at top dead center, you will feel a slight resistance because the wire is being squished, so you will have to apply a little force. Perform this operation several times to make sure that the wire is squished correctly.
05 / The squished wire should look something like this.
06 / Take a caliper and measure and measure the squish.
07 / In our case, squished part is 0.3 mm, which means that squish clearance is 0.3 mm.
For most cylinders, a squish clearance of 0.7 mm is recommended, such as for the Stage6 Racing cylinder kit.
08 / To achieve the desired 0.7 mm clearance, we have to use aluminum gaskets or spacers, which are normally supplied with the cylinder kits. We use a 0.4 mm thick gasket which we place under the cylinder. To ensure a good seal, you can use sealant on the front and back.
09 / After the appropriate gasket / spacer is placed, measure the squish again and check the value. If you have chosen the right gasket with the right thickness, the wire should now be squished by the recommended value of 0.7 mm. Now the engine can deliver its full power without the risk of engine damage.