Ok, let's have some help here.......

I don't have an inside mic so I had to measure the piston diameter and it came out 35 mm. Stroke is real dang close to
28 mm. So, doing the math I come out with 26.9 cc displacement.
pi r squared stroke
^ ^ ^
3.1416 X 17.5 X 17.5 X 28 = 26939.16 cubic millimeters/ 1000=
26.9 cubic centimeters.

Y'all ever seen a 27 cc engine? Or would it be a 25 cc engine?
What's 2 cc among friends unless it's in a syringe?

My measurements could be off slightly, I'm old and my reading glasses don't have long enough arms any more.