In what position should spark plugs be reinstalled after servicing from an opposed engine?

When reinstalling spark plugs in an opposed engine after servicing, it is essential to ensure that they are placed back in a manner that maintains optimal engine performance and functioning. The correct approach involves reinstalling the spark plugs next in firing order and also swapping them from bottom to top.

This method allows for better distribution of wear and thermal cycles among the plugs, ensuring that no single plug is subjected to excessive operational strain over time. When plugs are serviced, they may exhibit different wear patterns, and this provides an opportunity to balance their performance across the cylinders. By following the firing order and also swapping their positions, any discrepancies in individual plug performance can be mitigated, which contributes to smoother engine operation and a more uniform combustion process.

In contrast, returning the plugs to their original configuration would not take advantage of this balancing effect, and simply swapping them bottom to top without adhering to the firing order could disrupt the designed ignition sequence, leading to uneven performance. Therefore, the approach of using both the firing order and the repositioning enhances the longevity and efficiency of the engine.