Positioning No. 1 Piston at Top Dead Center (TDC)

The procedure described below assumes that the spark plug wires are correctly connected and the ignition distributor is correctly installed. If it becomes necessary to bring the engine to TDC to adjust the distributor position, the position of the No. 1 cylinder piston can be approximately determined by monitoring the change in compression pressure through the spark plug hole. Then align the appropriate alignment marks.

Top Dead Center (TDC) is the highest point of piston travel in its cylinder. Strictly speaking, in 4-stroke engines, each piston reaches this position twice per crankshaft revolution: once at the end of the compression stroke and once at the end of the exhaust stroke. When setting valve timing and ignition timing, the TDC position at the end of the compression stroke (usually No. 1 cylinder) is used in the vast majority of cases.

Positioning the piston(s) at TDC is required for many procedures, such as removal/installation of the camshaft, timing drive components and distributor.

Make sure the transmission is in Neutral, then firmly apply the parking brake or chock the rear wheels. Also disable the ignition system by disconnecting the electrical connectors of the primary (low tension) circuit of the ignition coil (refer to Engine Electrical Chapter). Remove the spark plugs (refer to Maintenance and Adjustments Chapter).

Any piston can be positioned at TDC by rotating the crankshaft using one of the methods described below. When viewing the engine from the front (drive belt side), the normal direction of crankshaft rotation is counterclockwise. Remember that rotating the crankshaft clockwise may disturb the timing belt adjustment.

a) The most effective method is to rotate the crankshaft in the normal direction using a socket wrench with a ratchet handle on the bolt threaded into the front end of the crankshaft;
b) A remote starter switch can save time (follow the manufacturer's instructions). Once the piston is close enough to TDC at the end of the compression stroke, stop the starter and perform the final adjustment using the method described in (a);
c) With an assistant, preliminary engine rotation can be performed in short bursts from the driver's seat under the operator's direction. The principle is the same as described in (b). Final adjustment is again performed manually using a socket wrench (see (a)).

PROCEDURE

1. Note the position of the No. 1 cylinder spark plug wire terminal on the distributor cap. If the terminal is not marked, trace the wire from the spark plug to the cap and make a mark yourself.

The No. 1 cylinder spark plug terminal on the distributor cap is normally identified as A1 (VTEC engines) or A (non-VTEC engines).

2. Remove the distributor cap and set it aside (refer to Maintenance and Adjustments Chapter).

3. Mark the distributor housing rim directly below the No. 1 cylinder terminal of the cap.

4. Rotate the crankshaft counterclockwise until the white TDC mark on its pulley aligns with the triangular notch of the pointer.

5. Now check the position of the distributor rotor; its tip should point exactly at the mark on the housing rim.
6. If the rotor is 180° away from the mark, the No. 1 piston is at TDC at the end of the exhaust stroke.
7. To bring the No. 1 piston to TDC at the end of the compression stroke, rotate the crankshaft one more full turn (360°) counterclockwise. The rotor tip should now point to the mark.
8. If all the above conditions for mark alignment are met, the task is complete: the No. 1 piston is at TDC at the end of the compression stroke.
9. Now, to bring the remaining pistons to TDC in firing order, mark the distributor housing rim for each cylinder (as done above for the No. 1 spark plug wire terminal). Rotating the crankshaft will inevitably turn the rotor; alignment of the rotor tip with the corresponding mark confirms that the next piston is at TDC at the end of the compression stroke.