2 stroke piston inertia formulas

[19jaguar75]

Hmm, the airplane engineering book says otherwise.
I have data for a couple balanced cranks so I am going to see which method works best, with and without those expansion forces.
That is once I get my crank balance spreadsheet finished.

I'm thinking it may be possible that the cylinder expansion forces, when the piston is not at TDC or BDC, could actually be a resultant upward force because some of the downward force is 1) at an angle to the crankshaft center and 2) a lot of its downward force is transferred into rotary motion of the crank wheels. So if the downward force that is felt by the crankshaft is less than the upward force that acts against the cylinder head then the resultant direction of force at the frame is upward.