Top dead center, often
abbreviated TDC, is the condition when a
piston is at the
apex of its
travel in the
cylinder. The
air chamber in the
cylinder is at it's lowest
volume. The
piston head, connecting
rod and
crankshaft journal where the
piston rod connects are all in a straight line thru the center line of the
cylinder.
Top dead center must be accurately located when adjusting the timing on an engine (usually expressed in degrees before or past top dead center - this figure is when the spark plug fires, causing the compressed gas/air mix to explode). There are usually marks on the crankshaft pulley and housing for a good reference as to when you should be close to top dead center on a particular cylinder. A timing light is necessary to insure the timing is properly adjusted.
This is only
applicable to
piston powered
internal combustion engines.
Rotary and
jet engines don't have
pistons.