Internal combustion engine

A twin cylinder engine (50, 300), includes a pair of cylinder members (74a, 74b) mounted to mounting surfaces (72a and 72b) of a crankcase (52), and cylinder heads (96, 324) mounted to the cylinder members. The cylinder members are modular components, which may be pre-assembled with components of the valve train as packaged units before the cylinder members are attached to the crankcase. Each cylinder member rotatably supports a cam gear (156) which extends into the crankcase for driving engagement with the crankshaft (58). The cylinder members may be configured for either side valve-type ("L-head"), or overhead valve-type ("OHV") engines, and the cylinder members may also be used in single cylinder engines. A twin cylinder engine (50, 300), includes a pair of cylinder members (74a, 74b) mounted to mounting surfaces (72a and 72b) of a crankcase (52), and cylinder heads (96, 324) mounted to the cylinder members. The cylinder members are modular components, which may be pre-assembled with components of the valve train as packaged units before the cylinder members are attached to the crankcase. Each cylinder member rotatably supports a cam gear (156) which extends into the crankcase for driving engagement with the crankshaft (58). The cylinder members may be configured for either side valve-type ("L-head"), or overhead valve-type ("OHV") engines, and the cylinder members may also be used in single cylinder engines.