@paulhunter123: the chain sprocket on the crankshaft is half the size (has half the number of teeth and is half the diameter) of the chain sprocket on the camshaft. Thus, for every two complete rotations of the crankshaft the camshaft turns only one rotation.
4 cylinder engine animation
Air-cooled motorcycle engine animation showing crankshaft, cam shaft, camchain, cam gears, valves, springs, pistons, connecting rods, and cylinders...
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codene said:
@paulhunter123: the chain sprocket on the crankshaft is half the size (has half the number of teeth and is half the diameter) of the chain sprocket on the camshaft. Thus, for every two complete rotations of the crankshaft the camshaft turns only one rotation.