MX | ROADRACE | KARTING | MOPED
To ensure the correct volume and squish, it's important to set the piston height in accordance with the specific piston height value pointed out on our insert boxes.
To measure the piston height, we've developed a clever measuring tool. There are 3 types available, depending on the engine's capacity; 85cc, 125cc and 250cc. This tool in combination with a dial indicator makes measuring the piston height quite easy!
Put the upper part of the tool on the flat bottom part. Also fit the dial indicator on the upper part, by tightening the screw on the side carefully.
Simultaneously make sure to adjust the little pointer to 5mm by moving the dial indicator in the upper part. The big pointer should indicate '0'. You can turn the outer ring of the dial indicator to ensure this.
Remove the cylinder head and put the upper part of the piston measuring tool, includig dial indicator, on top of the cylinder. Best to measure when the cylinder and gasket is mounted and the nuts tightened.
Rotate the crank to set the piston at Top Dead Center (it's highest point).
The big pointer turns clockwise and indicates the decimals of the piston height. The change in the little pointer indicates the milimeters of the piston height, which can be positive or negative. These numbers need to be added and substracted with 5mm.
The little pointer has turned counter clockwise to 7mm (+2mm) with the piston in TDC, and the big pointer turned clockwise to 0.16mm. Because we started with the little pointer at 5mm, this has to be substracted from the enumeration. This means that the piston height in this example is 7.16 - 5 = 2.16mm. The top of the piston is +2.16mm above the cylinder deck, meaning a positive piston height.
Here the little pointer has turned clockwise to 4mm (-1mm) and the big pointer turned clockwise to 0.32mm. Again, we started with the little pointer at 5mm, so this has to be substracted. This means that the piston height in this example is 4.32 - 5 = -0.68. The top of the piston is thus -0.68mm beneath the cylinder deck, meaning a negative piston height.