Which one of the following will not be affected when replacing piston #1 with piston #2?

When replacing piston #1 with piston #2, engine timing remains unaffected. Engine timing primarily refers to the synchronization of the camshaft and crankshaft, which dictates when the engine’s valves open and close in relation to the piston’s position in the cylinder. The pistons serve as the moving parts that facilitate combustion and help in generating power, but their direct interchangeability does not impact the timing of the engine.

In contrast, the replacement of pistons can influence other aspects such as compression ratio, power output, and fuel efficiency. The compression ratio can be altered if the replacement piston has different specifications in terms of size or design, directly impacting the engine's performance characteristics. Similarly, a change in the piston's design or weight can affect how efficiently the engine produces power and consumes fuel. Thus, while the replacement of one piston for another may change certain engine parameters, the timing remains stable unless other components of the timing system are also adjusted.