General information
Top dead center (TDC) is the highest point of the piston stroke in its cylinder. Strictly speaking, in 4-stroke engines, during the rotation of the crankshaft, this position is reached by each of the pistons twice: once at the end of the compression stroke and the second time at the end of the exhaust stroke. When adjusting the valve timing and setting the ignition timing angle, in the vast majority of cases, the TDC position of the end of the piston compression stroke is used (usually the first cylinder).
The need to bring the piston to the TDC position arises when performing many procedures, in particular such as removing/installing camshafts, timing drive components and ignition distributor.
Some engines are designed in such a way that when the crankshaft or camshaft is turned with the timing belt removed, the valves may come into contact with the piston crowns, which carries the risk of damage to the corresponding internal components, including destruction of the cylinder head casting.
Do not allow the shaft position to change after removing the belt!
Procedure execution order
1. Bringing any of the pistons to the TDC position is done by turning the engine crankshaft. If you look at the engine from the timing drive side, the normal direction of rotation of the crankshaft is clockwise. Remember that trying to turn the shaft counterclockwise can lead to a violation of the valve timing adjustments. The first is the outermost cylinder on the timing drive side.
2. Disconnect the negative battery cable. To make it easier to turn the engine, remove all spark plugs.
3. In order to gain access to the TDC mark on the camshaft gear, remove the upper timing belt cover (see section Removal and installation the timing belt cover).
4. Turn the crankshaft clockwise so that the camshaft cams that control the valves of the first cylinder are facing up with the narrowed part.
5. You can turn the crankshaft by rotating the front wheel with 5th gear set, or by rotating the crankshaft itself by the central bolt securing its pulley with the manual or automatic transmission in neutral and the parking brake engaged.
Do not turn the engine by the camshaft timing gear mounting bolt, as this may place excessive load on the timing belt.
6. Align the mark on the camshaft gear with the TDC mark on the timing belt cover. The mark on the crankshaft pulley (c14NZ engine) should match the mark on the lower timing belt cover. On engines X12SZ and C14SE the mark is located on the crankshaft gear. The piston of the first cylinder is in the TDC position.
C14NZ Engine TDC Timing Marks
TDC timing marks for X12SZ and C14SE engines
Material taken from an internet portal [Opelbook.ru]
Visitor comments