The valve mechanism consists of valves, 1 , push-rod, lifters and the camshaft. It makes air fuel mixture and 2 in and out of the engine at the proper time. The timing is conntrol by the 3 . As to most of the modern car engines, the camshaft is located over the 4 head, which is known as an 5 design. Some high-performance engines have two separate camshafts, one for each set of intake and exhaust valves. These enignes are known as 6 design. Each cam must revolve a 7 once during the four-stroke 8 to open. The camshft must revovle at exactly half the speed of the crankshaft. This is accomplished with a 2 : 1 ratio. A gear connected to the camshaft has twice the number of teeth as a gear connected to the crankshaft. The gears are linked in one of the 9 ways: 10 drive, chain drive and gear drive.