Duplex crankshaft sprocket for the TVR Speed 6 engine. This is the only duplex sprocket on the crankshaft and drives the lower or primary timing chain for the halftime sprocket and auxillary shaft. Both the other sprockets on the crankshaft are simplex or single row sprockets and are used to drive the scavenge and pressure oil pumps and water pump. This sprocket is the first sprocket to fit to the crankshaft. This simplex chain upgrade is available as a complete kit of new sprockets and drive chains and a complete new half time sprocket and shaft assembly.