A line of small internal combustion engines, including twin cylinder engines and single cylinder engines. The engines each include a crankcase, and one or more cylinder members attached to the crankcase, the cylinder members being separate components from the crankcase. A number of different crankcases are provided for various types of single and two cylinder engines, the crankcases having common mounting structure to which the cylinder members may be attached. Thus, the manner in which the cylinder members are attached to the crankcases is the same for each of the different types of crankcases. Two different types of cylinder members are provided, one having a side valve or “L-head” valve train, and the other having an overhead cam (“OHV”) valve train. The cylinder members are therefore modular components which may be selectively used in a variety of different types of engines.