Top Dead Center (TDC) for number one piston – locating

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 certain procedures such as camshaft and timing chain/sprocket removal.

3. Before beginning this procedure, be sure to place the transaxle in Neutral and apply the parking brake or block the rear wheels. Disconnect the negative battery cable from the remote ground terminal (see Engine electrical systems). Remove the ignition coils (see Engine electrical systems) and the spark plugs (see Tune-up and routine maintenance).

4. 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.

5. Rotate the crankshaft using a socket and breaker bar on the crankshaft pulley bolt 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.

6. Once the compression stroke has begun, TDC for the compression stroke is reached by bringing the piston to the top of the cylinder.
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.

7. This engine is not equipped with external components (crankshaft pulley, flywheel, timing hole, etc.) that are marked to identify the position of number 1 TDC. Therefore, the only method to double-check the location of TDC number 1 is to remove the valve cover to access the camshaft sprockets and alignment marks (Timing chain cover, chain and sprockets – removal, inspection and installation).

8. 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 120-degrees clockwise and following the firing order (refer to this Chapter’s Specifications). For example, rotating the engine 120-degrees past TDC number 1 will put the engine at TDC compres­sion for cylinder number 2.