How can you determine if the engine is at top dead center (TDC) during rocker arm adjustment?

Determining if an engine is at top dead center (TDC) during rocker arm adjustment is crucial for ensuring proper valve clearance and timing. When the engine is at TDC on the compression stroke, both the intake and exhaust valves for that cylinder should be closed, meaning there is no movement in the rocker arms for that specific cylinder.

The correct answer highlights that if rocker arm movement is detected, it indicates that the engine is on the exhaust stroke, not TDC on the compression stroke. During the exhaust stroke, the exhaust valve is closing, and the intake valve is beginning to open as the piston moves down. Therefore, any activity or movement observed in the rocker arms indicates that the piston has already passed TDC and the engine is moving toward the next stroke.

In contrast, the remaining choices do not accurately help in confirming TDC during rocker arm adjustment. The absence of crankshaft movement does not provide clear information regarding the position of the piston in relation to TDC, nor does oil leaking indicate anything about the compression stroke. The alignment of the timing mark with the case can be a useful reference point but does not provide definitive confirmation of the piston position without consideration of the specific stroke being analyzed.