Procedure of Valve Timing Setting

Procedure of Valve Timing Setting Points : procedure of valve timing setting, problems of camshaft and its drive system, problems in internal combustion engines, ic, engine, auto diesel When an engine is being reassembled after overhaul it is seldom difficult to obtain the correct valve and ignition timing; the timing marks on the camshaft gears or sprockets, which are sometimes rather indistinct, should show up reasonably clearly on clean parts and if the timing is done before the cylinder head is filled it is a simple matter to set the engine accurately to top dead-centre. If, however, the cylinder head has been installed or the engine is in the chassis, it will be necessary to locate the top-dead centre mark-and possible lines also indicating the inlet valve opening and exhaust valve closing points-either on the flywheel or on the fan pulley. On the majority of modem engines a small pointer on the edge of the pulley, a hole or a vee in the flange must be aligned with a pointer or a line on the valve timing cover. It is often difficult to distinguish the top-dead-centre marking on a flywheel when this can be viewed only through a small inspection aperture when the engine is in the chassis. If the rim is cleaned with a cloth dipped in paraffin and wrapped around a flat stick, the line will sometimes shown up more clearly. A useful tip is to apply a little aluminum paint to the rim of the flywheel in the approximately correct position and then to rub this off before it has dried. Some of the paint will be smeared into the indicator line, which will then show up more clearly.

Special Valve Clearance for Timing: The cams used on modern engines usually have ‘quietening” curves to reduce the acceleration and declaration rates of the valves. Consequently it is difficult to detect the exact point at which the valve begins to open, as the clearance is taken up very gradually. Many manufacturers, therefore, specify a larger valve clearance than normal for timing purposes The increased gap means that the tappet will strike the valve later, and more time for intake and exhaust.

Cardboard-disk method; if the valve timing is found to be incorrect, it will invariably mean removing the timing case cover and re-connecting the drive. The amount of dismantling involved will again be governed by the design. Using the makers timing marks wherever this is possible, in this case should make rectification. Sometimes the cardboard-disk method is used for checking valve timing.