Abstract: An internal combustion engine comprises a vertical crankshaft rotatable in a crankcase, a piston reciprocable along a cylinder axis, and a push rod tube. The push rod tube communicates between the crankcase and a rocker box, and is positioned below the cylinder axis and upwardly inclined with respect to the cylinder axis. A cam gear agitates oil in the crankcase so that the oil is conveyed through the push rod tube into the rocker box and returns through the push rod tube to the crankcase under the force of gravity. In another embodiment, the engine comprises a crankshaft having an arcuate throw and a crankpin. A connecting rod has a continuously formed big end installable over the arcuate throw to cooperate with the crankpin. A flywheel is mounted to the crankshaft on a side of the crank pin opposite a balancing web, and has a radially offset center of gravity to balance forces applied to the crankshaft through the connecting rod by the piston.