Locating and Setting Engine to Top Dead Center (TDC), Cylinder 1

Tools

• 15/16" or 24 mm socket (deep)
• Ratchet
• Flashlight
• Step stool
• Flywheel Lock P9206 (optional, depending on other work to be performed)

* If a deep 15/16" or 24 mm socket is not available, a shallow socket with a short extension (1–2") will work.

Procedure

Note: The crankshaft rotates twice for every single rotation of the camshaft. If the crankshaft is simply set to TDC without verifying the camshaft position, the engine may actually be at TDC on the exhaust stroke rather than the compression stroke for cylinder #1. After setting the crankshaft to TDC (by flywheel indication or actual piston position), always verify that the camshaft alignment mark is also at the TDC position.

1. This procedure can be performed by one person, though it is easier with two.
2. At the back of the engine compartment, looking from the left side of the car, locate the square opening (window) in the top of the clutch housing.
3. Look for the letters "OT" to appear in that opening as the engine is rotated.

Caution: The crankshaft should not be rotated — manually or otherwise — unless the timing belt is installed with timing properly set, or the camshaft housing assembly is removed. This is done to prevent valve/piston damage.

4. Using the 15/16" or 24 mm deep socket and ratchet, rotate the engine clockwise using the crankshaft pulley bolt on the front of the engine until the letters "OT" appear in the clutch housing window.

5. When the letters "OT" are visible, continue rotating clockwise until the scribe mark (line) beside the "OT" aligns with the tab inside the window. The tab is on the side of the window closest to the center of the car and extends down from the inside of the housing almost touching the flywheel.

6. An alternative TDC indicator is a 5 mm wide groove in the flywheel, visible through an opening in the bottom of the clutch housing near the starter. When the groove is centered in that lower opening, cylinder #1 is at TDC. This method is less preferred because if the groove is not precisely centered, the timing can be off ±1 tooth.

7. Alternatively, remove the #1 spark plug and insert a small-diameter wooden dowel into the spark plug hole until it contacts the top of the piston. Rotate the engine — the piston will force the dowel upward. When the end of the dowel is at its highest point, the engine is at TDC for cylinder #1.

8. If the engine is not in the car and the clutch housing is removed, the "OT" scribe mark on the flywheel will align with a cast mark on the back of the upper crankcase section when cylinder #1 is at TDC.

9. If the crankshaft pulley bolt needs to be removed, or if it is important that the engine remain at TDC, install the flywheel lock (P9206). (There is also an "engine out" flywheel lock P9130, used when the engine is on a stand to provide counter-torque for removing the crankshaft pulley bolt or flywheel cheesehead bolts — it is not intended to maintain TDC position.)

Note: The camshaft sprocket alignment mark, visible through the opening in the front distributor housing cover just above the distributor cap, can be used as a reference for locating approximate TDC when working alone. However, always use the flywheel for final alignment in case the timing is slightly off.