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 procedures such as camshaft and timing chain/sprocket removal.
3. Before beginning this procedure, place the transmission in Neutral or Park and apply the parking brake or block the rear wheels. Also remove the spark plugs (see Tune-up and routine maintenance). Warning: If method b) or c) in the next Step will be used to rotate the engine, disable the ignition system by disconnecting the primary electrical connectors at the ignition coils, and disable the fuel system (see Fuel pressure relief procedure).
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.
a) 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. Never turn the bolt counterclockwise.
b) A remote starter switch, which may save some time, can also be used. Follow the instructions included with the switch. Once the piston is close to TDC, use a socket and ratchet as described in the previous paragraph.
c) 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 switch. 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 (see 3.6L V6 engine). It should be a gauge with a screw-in fitting and a hose at least six inches long (see illustration).
4.5 A compression gauge can be used in the number one spark plug hole to assist in finding TDC
6. Rotate the crankshaft using one of the methods described above while observing for pressure on the compression gauge. The moment the gauge shows pressure indicates that the number one cylinder has begun the compression stroke.
7. Once the compression stroke has begun, TDC for the compression stroke is reached by bringing the piston to the top of the cylinder.
8. Continue turning the crankshaft until the notch in the crankshaft damper is aligned with the TDC mark on the timing chain cover (see illustration). At this point, the number one cylinder is at TDC on the compression stroke. If the marks are aligned but there was no compression, the piston was on the exhaust stroke. Continue rotating the crankshaft 360-degrees (1-turn) and realign the marks.
Note: If a compression gauge is not available, you can simply place a blunt object over the spark plug hole and listen for compression as the engine is rotated. Once compression at the No.1 spark plug hole is noted, the remainder of the Step is the same.
4.8 Align the groove in the damper with the TDC mark on the timing chain cover
9. After the number one piston has been positioned at TDC on the compression stroke, TDC for any of the remaining cylinders can be located by turning the crankshaft in increments of 120-degrees for 3.7L V6 engines or 90-degrees for 4.7L V8 engines and following the firing order (refer to the Specifications). For example on 3.7L V6 engines, rotating the engine 120-degrees past TDC #1 will put the engine at TDC compression for cylinder #6.
10. An even faster way to find TDC for any cylinder other than No. 1 is to make marks on the crankshaft damper 120-degree intervals from the TDC mark on the crankshaft damper (V6 engine) or 90-degree intervals from the TDC mark on the crankshaft damper (V8 engine). Install the compression gauge into the cylinder for which you want to find TDC, rotate the engine until compression begins to register on the gauge, then continue turning the crankshaft until the next mark on the damper aligns with the mark on the timing chain cover.