Note: The following procedure assumes that the distributor is installed correctly. If you want to find the TDC position in order to install the distributor correctly, you need to determine the piston position by feeling the compression on the spark plug hole of cylinder 1, and then align the spark timing marks, following the procedure described in step 8.
1. Top dead center (TDC) is the highest point in the cylinder that the piston reaches when driven into reciprocating motion by the crankshaft. All pistons reach TDC during the compression stroke and then again during the exhaust stroke, but in general it is common to associate the concept of top dead center with the compression stroke.
2. Setting the piston (s) to the TDC position is an essential part of many procedures, such as replacing the valve rocker arm, camshaft, timing chain and sprocket, ignition distributor, etc.
3. Before starting this procedure, place the gear shift lever in neutral and apply the parking brake or block the rear wheels of the vehicle. In addition, block the ignition system by disconnecting the primary cables from the distributor (low voltage) contacts. Remove the spark plugs (see chapter 1, section 32).
4. To set the piston to the TDC position, it is necessary to turn the crankshaft. There are several ways to do this, which will be discussed below. Usually the crankshaft is turned clockwise (if you look at it from the front wall of the engine).
- a) The most preferred method is that the crankshaft is rotated with a ratchet socket wrench (ratchet) by a bolt temporarily screwed into the front end of the crankshaft.
- b) You can also use a starter: this method gives some time gain. When the piston approaches the TDC position, continue turning the crankshaft with a socket wrench (see previous point).
5. Note the position of the N1 piston wire terminal on the distributor cap. If the terminal is not marked, locate it by tracing the location where the wire from the N1 piston spark plug enters the distributor cap.
6. Use a felt-tip pen or chalk to mark the position of the outlet on the distributor body.
7. Remove the cover from the distributor and set it aside (if necessary see section 33 chapter 1).
8. Turn the crankshaft (see above p.3) until the mark on the crankshaft pulley aligns with the "O" mark on the indicator.
9. Look at the distributor rotor: it should point to the mark you made on the distributor body.
10. If the rotor points in the opposite direction (rotated 180°), this means that piston N1 is at TDC on the exhaust stroke. To set the piston to the TDC position on the compression stroke, rotate the crankshaft clockwise one full revolution (360°). The rotor should now point to the mark on the distributor housing. So, piston N1 will be at TDC on the compression stroke when the distributor rotor points to the N1 piston wire terminal in the distributor cap and the installation marks are aligned.
11. After piston N1 has been set to TDC on the compression stroke, the TDC position for all other pistons can be found by turning the crankshaft 120° in the direction of normal rotation and following the firing order. Mark the positions of the remaining ignition circuit terminals on the distributor housing as you did for cylinder 1, and write the corresponding cylinder numbers next to the marks. When the crankshaft turns, the distributor rotor also rotates. When it points to one of the marks on the distributor housing, the piston in the corresponding cylinder will be at TDC on the compression stroke.
The article is based on data from the website: «ChevyMan.ru»