Providing a
cam for lifting and lowering the
exhaust valve so that the
exhaust gas return-flow from one cylinder to another cylinder can be realized as greatly as possible, wherein the pistons and the exhaust valves do not come in contact with each other, and the valve control method does not depend on an electronic control approach. An exhaust
cam for lifting and lowering the
valve lift of the
exhaust valve of one of the cylinders wherein the
cam profile of the exhaust cam regarding the one of the cylinders including, but not limited to: a main exhaust lobe part for opening the
exhaust valve so that the
exhaust gas is discharged out of the cylinder; and, a gas return lobe part for opening the exhaust valve so that the quantity of the
exhaust gas from the one of cylinders to the other cylinder is increased, the gas return lobe part being formed on the cam-follower descending part of the profile so as to
delay the closing timing of the exhaust valve or maintain the
valve lift-displacement regarding the exhaust valve larger, and wherein the cam profile is formed so that the interference between the exhaust valve and the
piston is evaded and the overlap regarding the exhaust valve of the one cylinder and the exhaust valve of the other cylinder is increased by the manner that the main exhaust lobe part and the gas return lobe part rise outward from the base circle.