The procedure described below is based on the assumption that the ignition distributor (if it exists) installed correctly. If you are trying to bring the piston to TDC in order to set the distributor correctly, the piston position should be determined by the presence of pressure in the #1 spark plug hole, after which you should align the spark marks or insert the spark timing tool into the flywheel, depending on the model.
Cylinder #1 is the cylinder closest to the radiator.
Top dead center is the extreme upper position of the piston as it moves up and down in the cylinder when the crankshaft rotates. Each piston reaches TDC at the end of both the compression stroke and the exhaust stroke, but it is common to consider the upper position of the piston at the end of the compression stroke as the engine's TDC.
Setting the TDC position is an integral part of many procedures such as removing the timing belt or chain and removing the distributor.
Before starting the procedure, make sure the transmission is in neutral and set the parking brake or block the rear wheels. Also, disable the ignition system by disconnecting the coil wire from the center terminal of the distributor cap and grounding it to the cylinder block with a wire. Remove the spark plugs (see chapter Routine car maintenance).
1. To bring any piston to the TDC position, rotate the crankshaft using one of the methods described below. When looking at the engine from the front, the normal direction of rotation of the crankshaft is clockwise.
2. The most preferred method of turning the crankshaft is with a replaceable head and ratchet mechanism attached to a bolt screwed into the front of the crankshaft.
3. You can also use a remote starter switch, which can save you some time. Follow the instructions that come with the switch. Once the piston is as close to TDC as possible, use the socket and ratchet as described above.
4. If you have an assistant who can set the ignition switch to the "Start" position with short jerks, you can bring the piston closer to TDC without the remote starter switch. After your assistant leaves the car, complete the procedure using the socket and ratchet as described in point "a".
5. Note the location of the terminal on the distributor cap for the #1 spark plug wire. If the terminal is not marked, trace the wire from the #1 cylinder spark plug to the cap (#1 is the cylinder closest to the radiator).
6. Using a felt-tip pen or chalk, make a mark directly below terminal #1 on the distributor housing or gear cover.
7. Remove the dispenser cover and set it aside (if necessary, see Chapter Routine car maintenance).
8. Turn the crankshaft so that the timing marks (on the front of the engine) matched. The M40 engine does not have timing marks on the front, instead it has a timing hole in the flywheel that must be aligned with a hole in the rear flange of the cylinder block. For this engine, turn the crankshaft until the distributor rotor is close to TDC, and then continue turning until a drill bit of the appropriate diameter can enter the holes in the cylinder block and flywheel at the same time.
9. Look at the distributor runner - it should point directly to the mark you made on the distributor housing or gear cover.
10. If the runner points in the opposite direction by 180°, then piston No.1 is at TDC, but in the exhaust stroke.
11. To bring the piston to TDC on the compression stroke, rotate the crankshaft one full revolution (360°) clockwise. The rotor should now point to the mark on the distributor or gear cover. When the rotor points to the #1 spark plug wire terminal on the distributor cap and the timing marks are aligned, piston #1 is at TDC on the compression stroke.
If the ignition marks cannot be aligned when the rotor points to the mark, the timing belt or chain may have skipped a few teeth on the sprocket or been installed incorrectly.
12. Once piston #1 has been brought to TDC, TDC for the remaining pistons can be reached by rotating the crankshaft in the established firing order. Note the position of the remaining spark plug wire terminals in the same way as you did for terminal #1, then number the marks according to the cylinder numbers. As you rotate the crankshaft, the rotor will also turn. When it points directly at one of the marks on the distributor, the piston for that particular cylinder will be at TDC on the compression stroke.
[The original is located on the internet portal «BMWMAN.RU»]