Before we go further, we need to consider the fundamentals.

LOADING
Engine negative torque calculations
P1V1 = P2V2,
Where per 55cc cylinder,
P1 = ambient pressure = 101325N/m^2
V1 = 45288.8 mm^3 - calculated volume enclosed after the top of the piston passed the exhaust port.
V2 = 7525.8 mm^3
Resulting in P2 = P1V1/V2 = 607950N/m^2
Nett pressure acting on combustion face of the piston = P2 – Ambient pressure P1 = 607950-101325 = 506625N/m^2
Piston Area, A = (pie)r^2 where r = 0.0225meter, therefore A = 0.00159m^2
Force on the piston = Nett Pressure x Area = 506625 x 0.00159 = 805.5N
Torque = Force x Distant, where distant is between the centroid of piston rod pin (on the crankshaft) to crankshaft center, in this case it is 17.5mm or 0.0175m.
T = 805.5N x 0.0175m = 14.1Nm

The value above is based only on one cylinder of 55cc jug.