Improved internal combustion engine, particularly, an improved two-stroke, diesel aircraft engine. A first improvement includes a wrist pin/connection rod assembly. A plurality of fasteners extend through a wall of a wrist pin and into a wrist pin insert to secure the wrist pin to a cradle-like portion of a connecting rod. A second improvement includes a fuel injection system which cools fuel injectors with overflow fuel from a fuel pump. The overflow fuel is warmed as it cools the fuel injectors, thereby preventing ice-build up on a fuel filter in cold weather as the overflow fuel is recirculated to the fuel pump. A third improvement includes a new cylinder head cooling arrangement. The cylinder head and a cooling cap define an annular cooling passageway. Cooling fluid flows through the annular cooling passageway to cool the cylinder head. The cooling cap includes an inlet port and an outlet port which are not diametrically opposed. Accordingly, the annular cooling passageway includes a restricted portion to ensure cooling fluid flows completely around the annular cooling passageway to better cool the cylinder head. The cooling cap is adjustably mounted on the cylinder head, so that the cooling cap can be coupled to a cooling jacket independent of the location of the cylinder head on the engine or cylinder block, as when the cylinder head threads into the engine block. The same clamping device used to connect the cooling cap to the cylinder head can be used to secure the fuel injector to the cylinder head. A fourth improvement includes a cross-feed cooling passageway extending between multiple cylinder banks to provide thermal coupling between the cylinder heads and the lower crankcase of the engine, and to provide a safety arrangement for continued cooling fluid flow at least in the event a thermostat in communication with a cooling jacket should fail.