an engine block is provided including multiple cylinders having pistons reciprocal therein connected to separate crankshaft sections journalled from the block by connecting rods . the block also journals a countershaft to whose opposite ends the crankshaft sections are drivingly connected through the utilization of power transmitting assemblies each including a clutch assembly and releasable drive connection structure incorporating and indexing mechanism for indexing the corresponding shaft section to the countershaft in the same indexed position each time the corresponding clutch assembly is actuated . the clutch assembly of each power transmitting assembly is interposed , in the path of transmission of power from the corresponding crankshaft section to said countershaft , intermediate the crankshaft section and the corresponding drive connection structure .