Note. The description of the procedure below is based on the assumption that the BB spark plug wires are connected correctly and the ignition distributor is installed. If it becomes necessary to bring the engine to TDC in order to correct the position of the distributor, the position of the piston in the first cylinder of the engine can be qualitatively determined by monitoring the change in compression pressure through the spark plug hole. Next, you need to achieve the combination of the corresponding installation marks.
1. 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, each of the pistons reaches this position 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, in the vast majority of cases, the TDC position of the end of the piston compression stroke is used (usually the first cylinder).
2. The need to bring the piston (to her) to the TDC position occurs during many procedures, in particular, such as removing / installing camshafts, timing drive components and an ignition distributor.
3. Make sure the transmission is in neutral, then firmly apply the parking brake or chock the rear wheels of the vehicle. Also immobilize the ignition system by disconnecting the coil wire from the distributor cap and grounding it to the block ground. Remove spark plugs (see chapter Settings and ongoing maintenance).
4. Bringing any of the pistons to the TDC position is done by turning the engine crankshaft in one of the ways described below. Looking at the engine from the front (from the drive belt), the normal direction of rotation of the crankshaft is clockwise. Remember that attempting to turn the shaft counterclockwise can lead to a violation of the timing belt adjustments:
- a) The most effective method is to turn the shaft in the normal direction using a bolt screwed into the end of its front trunnion using a ratchet-driven socket wrench;
- b) Save time with remote starter switch (follow the manufacturers instructions). As soon as the piston is close enough to the TDC of the end of the compression stroke, the starter stops and further adjustment is carried out by the method described in paragraph (A);
- c) With the presence of an assistant, the preliminary cranking of the engine can be carried out in short jerks from the driver's seat under the guidance of the operator. The principle is the same as described in paragraph (b). The final adjustment, again, is done manually, using a socket wrench (see point a).
5. Remember position of the plug of connection of a candle wire of the first cylinder on a cover of the distributor. If the terminal is unmarked, run the wire from the spark plug to the cap and mark accordingly yourself.
6. Using a marker or chalk, mark the rim of the distributor housing at a point just below the first cover cylinder terminal.
7. Remove the cap from the distributor and set it aside (see chapter Settings and ongoing maintenance).
8. Turn the crankshaft clockwise so that zero (yellow) the TDC mark on its pulley is aligned with the triangular pointer on the timing belt cover.
Note. There are several alignment marks on the pulley: from 0 (TDC) up to 30°in 5°increments. Zero is the leftmost mark (looking from the front), which is usually tinted yellow.
9. Now check the position of the distributor slider - it should turn out to be with its nose turned exactly to the mark on the body rim.
10. If the slider is rotated 180°relative to the mark, therefore, the piston of the first cylinder is in the TDC position of the end of the exhaust stroke.
11. In order to bring the piston to TDC of the end of the compression stroke, turn the crankshaft one more full turn (360°) clockwise. Now the slider should turn around with its nose towards the mark.
12. If all the above conditions for the alignment of the marks are met, the task can be considered completed - the piston of the first cylinder is brought to the TDC position of the end of the compression stroke.
13. Now, in order to alternately, in the order of ignition, bring the remaining pistons to TDC, apply the appropriate marks on the rim of the distributor housing (as it was done above for the terminal for connecting the first spark plug wire). Cranking the crankshaft will inevitably be accompanied by the rotation of the slider, 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.
Note. To go from the TDC of one cylinder to the TDC of the next, the crankshaft must be rotated 120°.