Note. The description of the procedure below is based on the assumption that the installation of the BB spark plug wires and the ignition distributor is correct. 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 (see paragraph 9).
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 of the end of the piston compression stroke is used (usually the first cylinder).
The need to bring the piston (to her) to the TDC position occurs during many procedures, in particular, such as removing / installing the camshaft, timing drive components and ignition distributor.
1. Make sure the transmission is in neutral, then firmly apply the parking brake or chock the rear wheels of the vehicle.
2. Immobilize the ignition system by disconnecting the electrical connectors of the distributor (see chapter Engine electrical equipment).
3. Temporarily disable the power system (see chapter Power and exhaust systems).
4. Remove spark plugs (see chapter Current service).
5. 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 counterclockwise. Remember that attempting to turn the shaft clockwise 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 the 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 stated in paragraph (b). The final adjustment, again, is done manually, using a socket wrench (see point a).
6. Remember position of the plug of connection of a candle wire of the first cylinder on a distributor cover. If the terminal is unmarked, run the wire from the spark plug to the cap and mark accordingly yourself.
7. Remove the cap from the distributor and set it aside (see chapter Current service).
8. Mark the body at a point directly below the terminal of the first cover cylinder (see accompanying illustration).
9. Find the alignment marks on the crankshaft pulley. The mark highlighted in white corresponds to the TDC position. Now, turning the crankshaft in the normal direction (see paragraph 5), achieve the exact alignment of this mark with the pointer on the bottom cover of the timing belt (see accompanying illustration).
10. Now check the position of the distributor slider - it should be deployed with a spout exactly on the mark on the body. 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°) counterclock-wise. 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 corresponding piston has been brought to TDC at the end of the compression stroke.