What is the most critical adjustment when shimming a lower unit?

When shimming a lower unit, the most critical adjustment is the pinion depth or height. This adjustment is crucial because it directly affects the engagement of the drive gears within the lower unit assembly. Proper pinion depth ensures that the pinion gear meshes correctly with the drive gear, allowing for smooth operation without excessive backlash or binding.

If the pinion depth is not set correctly, it can lead to premature wear on the gears, increased noise during operation, and ultimately failure of the lower unit. It is also essential for maintaining optimal performance and efficiency. Precise adjustments here help to ensure the longevity and reliability of the entire propulsion system.

While gear alignment, output shaft positioning, and sealing surface alignment are also important factors in the overall setup and functionality of the lower unit, they do not have the same critical impact on gear meshing and performance as pinion depth does.