The following procedure 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 properly install the distributor, then the position of the piston must be determined by the presence of pressure in the hole for spark plug No. 1, after which you should align the ignition marks or insert a timing tool into the flywheel, depending from the model.
Cylinder #1 is the cylinder closest to the radiator.
Top dead center is the topmost position of the piston as it moves up and down in the cylinder as the crankshaft rotates. Each piston reaches TDC at both the end of the compression and exhaust strokes, but it is common to take the TDC of the engine to be the top position of the piston at the end of the compression stroke.
Setting to TDC is an integral part of many procedures such as removing the timing belt or chain and removing the ignition distributor.
Before starting the procedure, make sure the transmission is in neutral and set the parking brake or block the rear wheels. Also, turn off 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 spark plugs (see chapter Car maintenance).
1. In order 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 way to crank the crankshaft is with an interchangeable head and ratchet attached to a bolt screwed into the front of the crankshaft.
3. You can also use a remote starter switch to save some time. Follow the instructions that came with the switch. Once the piston is as close to TDC as possible, use the replacement head and ratchet as described above.
4. If you have an assistant who can set the ignition switch to the «Start» short jerks, you can bring the piston closer to the TDC position without the remote starter switch. After your assistant has left the vehicle, complete the procedure with the replacement head and ratchet as described in paragraph «A».
5. Note the position 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 (cylinder number 1 - closest to the radiator).
6. With a felt-tip pen or chalk, make a mark directly under terminal No. 1 on the distributor housing or on the gear cover.
7. Remove the distributor cap and set it aside (if necessary, see chapter 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 at the front, instead it has a timing hole in the flywheel that must be aligned with the hole in the rear flange of the cylinder block. For this engine, crank the crankshaft until the distributor runner approaches TDC, and then continue cranking until a drill of the right diameter can enter the holes in the cylinder block and in the flywheel at the same time.
9. Look at the distributor slider - it should point directly to the mark you made on the distributor housing or on the gear cover.
10. If the slider points in the opposite direction 180°, then piston #1 is at TDC but on the exhaust stroke.
11. To bring the piston to TDC on the compression stroke, rotate the crankshaft one full revolution (360°) clockwise. Now the slider should point to the mark on the distributor or gear cover. When the slider points to the #1 spark plug wire terminal on the distributor cap and the ignition timing marks are aligned, the #1 piston is at TDC on the compression stroke.
If it is not possible to align the ignition marks when the slider points to the mark, then it is possible that the timing belt or chain has skipped a few teeth on the sprocket, or has been installed incorrectly.
12. After the No. 1 piston is brought to the TDC position of the end of the compression stroke, the TDC for the remaining pistons can be achieved by turning the crankshaft in the prescribed cylinder firing order. Note the position of the wire terminals of the remaining spark plugs in the same way as you did for terminal #1, then number the marks according to the cylinder numbers. When turning the crankshaft, the slider will also turn. When it points directly to one of the marks on the distributor, the piston of this particular cylinder will be in the TDC position of the compression stroke.