1. Spark Plug Check:
Remove the spark plug from the number one cylinder.
Slowly rotate the engine by hand using a wrench on the crankshaft bolt (not the starter motor).
As you rotate the engine, feel for compression. When you feel pressure pushing back against your hand, stop turning.
Observe the position of the piston through the spark plug hole; if it is at the highest point, it's at TDC.
If the piston moves down as you rotate the engine, you've gone past TDC. Continue turning until you feel compression again and check the piston position.
2. TDC Indicator:
Some engines have a small hole or window near the flywheel or timing cover that allows you to see the TDC indicator mark.
As you slowly rotate the engine, look for the TDC mark to align with a pointer or notch. This indicates that the engine is at TDC.
3. Rocker Arm Movement:
If your engine has exposed rocker arms, you can use them as an indicator of the piston's movement.
For the compression stroke, the intake valve should be closed and the exhaust valve should be opening or just about to open.
Check the rocker arms associated with these valves to see if they are loose.
If both the intake and exhaust valves are loose, the piston is likely on its exhaust stroke.
To confirm that it's the number one cylinder, ensure the distributor rotor (if applicable) is pointing towards the number one spark plug wire position on the distributor cap.
By following these methods, you can accurately determine if the engine is at TDC on the compression stroke for the number one cylinder and proceed with any necessary adjustments to the timing.
