A four-crank engine has the two outer cranks set at 120° to each other, and their reciprocating masses are each 400 kg. The distance between the planes of rotation of adjacent cranks are 0.5, 0.8 and 0.6 m. If the engine is to be in complete primary balance, determine the reciprocating mass and the relative angular position for each of the inner cranks.

If the length of each crank is 0.3 m, the length of each connecting rod 1.2 m and the speed of the engine 240 rpm, what is the maximum secondary unbalanced force?