Engine Timing Gears

Timing Gears: 

The camshaft and the crankshaft are connected by Gears or chains. When connected by gears, they move in opposite directions. they move in opposite directions. When connected by chain, they move in the same direction. The camshaft and crankshaft are are connected such that there is correct relationship between the motions of the piston and valves. In order to ensure this, timing marks are provided on chain sprockets or gears of the two shafts. These timing marks work as guideline to the mechanic at the time of assembly.

Valve Operating Mechanism: 

Two types of valve operating mechanism are use in engine:

Side Valve mechanism : A cam mounted on a rotating camshaft operates the tapped, which further actuates the stem guide and is seated on valve seats when closed. A valve spring, fitted between a section of a block and a valve retainer locked with bottom end of the valve stem, acts to close the valve when the cam moves in the closing position.

Overhead valve mechanism : It has two additional moving parts, i.e. a push rod and a rocker arm. The cam lifts the valve lifter, which actuates the rod. The push rod in turn, causes the rocker arm to rotate about a shaft. The other end of the rocker arm pushes down the valve against the pressure of the valve spring.

Valve clearance :

     A clearance 0.3 mm is given to ensure that the valve fully closes. The clearance is measured with a feeler gauge when the follower is on the back of the cam.