timing gear

noun

(in an internal-combustion engine) the drive between the crankshaft and the camshaft, usually giving a ratio of 2 : 1

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012