The volume of the combustion chamber with the piston at top dead centre (TDC) should be 0.48 - 0.52 cc according to our experience, depending on pipe and prop. Thinner pipes will allow smaller volumes without detonation problems, smaller props allow a bigger volume. New engines are set by me at appr. 0.50 cc.
This means that the distance between the top of the piston at TDC and the squish band of the head will be in the order of .45 mm. Figure 1 shows how to measure the squish clearance.

The piston has a dome. The height of the dome is 0.90 mm, the dome radius is 61.7 mm.
These are values to start with using Globee plugs. We have no experience in using other plugs.
Our experience, like anyone's, is limited however. Use your own ideas to find the optimum combinations of compression, pipe, prop and needle settings!

fig1: Measurement of squish clearance. This can be done either with the piston in top position (not so easy with a tight piston fit) or with piston in bottom position and correct for stroke of 18.95mm.


Back to Homepage