base gasket

[93mustang97sea]

This is a random questions since I'm not up to this step while rebuilding my 787 motor but I was just thinking about it so here it is.
How do you figure out the right base gasket you need?

 

[seadooya]

With base gasket installed (start with a 0.5 or 0.6mm), cylinders bolted down, and head bolted on, insert a piece of solder so as to position the end over the piston pin at the edge of the cylinder wall.
While holding the solder in place, rotate the engine past TDC so as to compress the solder between the edge of the piston and cylinder.
Remove the solder from the cylinder and measure it.
Repeat the procedure for the opposite side of the same cylinder.
Repeat all above for the other cylinder. You now should have 4 measurements logged.
Check the chart below to see where you’re at. The lowest and highest values observed for both cylinders should be within the specs for your engine model. If your gap is too small or large, change the base gasket to compensate.

787 / 1.2-1.6 mm (.047-.063 in)

 

[93mustang97sea]

787 / 1.2-1.6 mm (.047-.063 in)

I take it the lower the number the higher the compression?

 

[Dr Honda]

I take it the lower the number the higher the compression?

Yes, but he "Squash Band" creates high velocity, to help to keep the piston edges cool. If you put it to the tightest point, and you get a slightly lean run, you could have problems. (too much heat) This is why you can't just "Mill" the head on a Rotax engine. When you cut it down to create higher compression... you have to re shape the squish band also.

Personally, unless you run premium fuel all the time... I would shoot for the center of the spec.