Squish bands?
 

I am converting an OPS maxi 30cc. This is an older glow engine with bearings all around and comes with a "walbro" type carb, it also takes a standard walbro as a bolt on.

The head is a turned disk that is held down by the head cover piece that you see. The current "head disk" is made for a glow plug and too thin for a CM-6 plug. It has about 0.040" squish band clearance as designed. The inside countour of the head is basically rectangular with rounded corners. Since I am making a new head disk should I make any changes? Tighter squish band? Increase or decrease the volume of the chamber? If I did want to change the volume of the chamber how do I detemine final compression ratio and what should that be? 10:1 for regular gas? So that is 3CC for this 30CC engine? Put it on a scale and see how much water it hold in grams? Grams = CC.

RE: Squish bands?
 

10:1 is OK for a CR based on stroke volume. Measure with oil and a small calibrated 5cc syringe.
reduce the squish clearance to less than 0.020", preferably to about 0.015" if you want to take full advantage of it. Transition from combustion bowl to squish zone must be sharp, without radius.

I advise you to do some reading on the subject. Jennings is a good place to start.

RE: Squish bands?
 

I second pe's recommendations. Jennings book is excellent to get started.

RE: Squish bands?
 

I have a copy of Jenning's 2-stroke Tuner's guide on every computer I use. I have also made paper copies to read during down time at work. Good Stuff.

I made the head insert for the CM-6 plug today. I tightened up the squish band a little. I made the cavity the same as the original head insert.