The cranks of {HEAD ~ adjacent pairs} of {TAIL ~ cranks} are interconnected by a common crankshaft, therefore all of the cranks are interconnected and rotate together about a common axis 
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The cranks of { HEAD ~ adjacent pairs } of { TAIL ~ cranks } are interconnected by a common crankshaft , therefore all of the cranks are interconnected and rotate together about a common axis
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH