Top Dead Center (TDC) for number one piston — locating
1. Top Dead Center (TDC) is the highest point in the cylinder that each piston reaches as it travels up the cylinder bore. Each piston reaches TDC on the compression stroke and again on the exhaust stroke, but TDC generally refers to piston position on the compression stroke.
2. Positioning the piston (s) at TDC is an essential part of many procedures such as valve adjustment and camshaft and timing chain/sprocket removal.
3. Before beginning this procedure, be sure to place the transmission in Neutral and apply the parking brake or block the wheels. If method b) in the next Step will be used to rotate the engine, disable the fuel system (see Fuel pressure relief procedure), then disconnect the electrical connectors from the ignition coils (see Engine electrical systems).
4. In order to bring any piston to TDC, the crankshaft must be turned using one of the methods outlined below. When looking at the front of the engine, normal crankshaft rotation is clockwise.
- ) The preferred method is to turn the crankshaft with a socket and ratchet attached to the bolt threaded into the front of the crankshaft. Turn the bolt in a clockwise direction only.
- ) If an assistant is available to turn the ignition switch to the Start position in short bursts, you can get the piston close to TDC without a remote starter Make sure your assistant is out of the vehicle, away from the ignition switch, then use a socket and ratchet as described in Paragraph (a) to complete the procedure.
5. Install a compression pressure gauge in the number one spark plug hole. It should be a gauge with a screw-in fitting and a hose at least six inches long.
6. Rotate the crankshaft using one of the methods described above while observing the compression gauge. When TDC for the compression stroke of number one cylinder is reached, compression pressure will show on the gauge as the marks on the crankshaft pulley are beginning to line up (see illustration). If you go past the marks, release the gauge pressure and rotate the crankshaft around two more revolutions.
3.6 Turn the crankshaft until the notch in the pulley aligns with the zero on the timing plate
7. After the number one piston has been positioned at TDC on the compression stroke, TDC for the next cylinder in the firing order can be located by turning the crankshaft another 120-degrees (refer to the firing order in this Chapter’s Specifications).