Hellow, I came upon this problem when working out the power developed in the cylinder of a double-acting steal engine. A brief explanation of the motion of the piston in a reciprocating engine is neccessary; In the simple case of a crank revolving at a constant rate, say one rpm, the piston is at rest at either end of the stroke, then first accellerates towards the crank, until 90 degrees after centre, when the direction of the accelleration changes, to bring the piston to rest at the other end of the stroke. My question is this; If the crank is doing work on the piston, after ninty degrees after centre, to slow it down from its max velocity,and bring it to rest at the end of the stroke, can pressure on the piston acting in the opposite direction, trying to accelerate the crank, be doing any work on it? Steam engineers evidently believe that it can, though the physics would seem to indicate that the only time that the piston can accellerate the crank is during the first ninty degrees of rotation after centre. For anyone looking in detail at the piston motion, the accelleration caused by the angluraity of the connecting rod must also be taken into account.Though in steam engines with connecting rods several times longer than the stroke, this is much less than the typical values in ic engines.........here is a link to a site with explanation of piston velocity and accelleration; http://www.epi-eng.com/piston_engine_technology/piston_velocity_and_acceleration.htm Regards, afternoonslow.