When removing an engine cylinder, at what piston position should the piston be?

When removing an engine cylinder, the piston should be at top dead center (TDC) to ensure that the cylinder head is not under pressure from combustion gases. At TDC, the piston is at its highest point in the cylinder and is not blocking any of the cylinder ports, which is crucial for preventing any potential damage or interference when detaching the cylinder. This position also allows easy access to the cylinder's components such as the pushrods and valves.

Being at TDC minimizes the risk of the valves being open, which could lead to them getting damaged. Moreover, having the piston at this position helps in maintaining the alignment of the cylinder and the crankshaft. This makes the process of removal smoother and safeguards the internal components of the engine.

The other options suggest different piston positions that may not provide the same safety and ease during cylinder removal. For instance, if the piston were at bottom dead center or halfway between positions, there could be complications due to valve extension and cylinder pressure that could hinder the removal process and pose risks to the engine's integrity and components.