Note. The following procedure is based on the assumption that the spark plug wires are connected correctly and the distributor is installed correctly. If it is necessary to bring the engine to TDC in order to adjust the distributor position, the piston position in the first cylinder of the engine can be determined qualitatively by monitoring the change in compression pressure through the spark plug hole. Next, it is necessary to achieve alignment of the corresponding installation marks. Top dead center (TDC) is the highest point of the piston stroke in its cylinder. Strictly speaking, in 4-stroke engines, this position is reached by each piston twice during crankshaft rotation: 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 (usually the first cylinder) is used.
The need to bring the piston(s) to the TDC position arises when performing many procedures, in particular such as removing/installing the camshaft, timing drive components and ignition distributor.
Make sure the transmission is in neutral, then firmly set the parking brake or chock the rear wheels of the vehicle. Also immobilize the ignition system by disconnecting the coil high-voltage wire from the distributor cap and grounding it to the engine block with a jumper wire. Remove the spark plugs (see Chapter Settings and ongoing maintenance).
Bringing any of the pistons to the TDC position is done by turning the engine crankshaft in one of the ways described below. When looking at the engine from the front (from the drive belt side), the normal direction of rotation of the crankshaft is clockwise:
- a) The most effective method is to turn the shaft in the normal direction by the bolt screwed into the end of its front journal using a socket wrench with a ratchet drive - remove the lower protective screen from the passenger side of the car;
- b) A time-saving measure is to use a remote starter switch (follow the manufacturers instructions). As soon as the piston is close enough to TDC on the compression stroke, the starter stops and further adjustment is made using the method described in (a);
- c) If an assistant is available, the engine can be pre-cranked by short jerks from the driver's seat under the operator's guidance. The principle is the same as described in point (b). The final adjustment is again made manually, using a socket wrench (see point a).
1. Remember the position of the spark plug wire connection terminal for the first cylinder on the distributor cap.
2. If the terminal is not marked, follow the wire from the spark plug to the cover and make a corresponding mark yourself (use a scriber or marker).
3. Remove the distributor cap and set it aside (see Chapter Settings and ongoing maintenance).
4. Turn the crankshaft clockwise so that the white TDC mark on its pulley aligns with the triangular indicator on the timing belt cover.
Note: There are two timing marks on the pulley. The second mark is painted red and is used only to set the ignition timing angle using a stroboscope.
5. Now check the position of the distributor rotor - it should be turned with its nose exactly on the mark on the rim of the housing. If the rotor is turned relative to the mark by 180°, then the piston of the first cylinder is in the position of TDC at the end of the exhaust stroke. In order to bring the piston to TDC at the end of the compression stroke, you should turn the crankshaft one more full revolution (360°) counterclockwise. Now the rotor should turn with its nose towards the mark.
6. Loosen the screw and set the inspection cover aside, thereby providing access to the timing marks on the camshaft gears of both cylinder banks. Through the hole in the timing belt cover, make sure that the timing mark on the camshaft gear is aligned with the mating mark on the rear cover.
7. When all the marks (on the crankshaft pulley and the camshaft gear) are aligned, the piston of the first cylinder can be considered to be brought to the TDC position at the end of the compression stroke.
8. Now, in order to bring the remaining pistons to TDC one by one in the order of ignition, the crankshaft should be turned clockwise in 120° increments, moving from cylinder to cylinder in the order of ignition. Apply the corresponding marks on the rim of the distributor housing (as was done above for the terminal for connecting the first spark plug wire). Turning the crankshaft will inevitably be accompanied by rotation of the runner, the alignment of the nose of which with the corresponding mark will confirm that the next piston has been brought to TDC at the end of the compression stroke.