An overhead valve engine including a cylinder bore having an outer end; and a crankshaft assembly including a substantially straight crankshaft, a substantially cylindrical journal eccentrically mounted on the crankshaft, a one-piece connecting rod rotatably mounted on the journal, and a counterweight mounted on the crankshaft. The engine also includes a cam shaft having at least one cam surface and an axis inward of the outer end of the cylinder bore; two valves having opened and closed positions; two valve stems, each valve stem being attached to a valve; and two generally L-shaped and pivotably mounted valve operating levers, each lever including a first lever arm having a cam follower in contact with the cam surface, a pivot axis about which the lever pivots, and a valve arm in contact with a valve stem, where movement of the lever caused by the cam surface causes the lever to pivot and the valve arm to depress the valve stem and thus open the valve.