YAMAHA VERTICAL SHAFT UPPER SEAL 93104-20M02

Function and technical context

This upper seal on the vertical shaft acts as a sealing barrier in the connection area between the outboard motor and the Yamaha steering rod, preventing seawater from entering the internal cavities of the transmission system. Installed on top of the vertical shaft, it seals the interface where the shaft rotates continuously, subjected to steering and acceleration movements. Its proper operation is critical to preserve the integrity of the transmission oil and prevent internal corrosion caused by salt water infiltration, which can cause premature wear of gears, bearings and titanium components.

When to replace this part?

Symptoms of upper seal failure include the presence of water or oily emulsion in the transmission reservoir, progressive oil loss during navigation, or visible corrosion on internal metal parts after maintenance inspections. It is recommended to check its condition during each seasonal maintenance and replace it preventively every 5-7 years of regular use or after any repair that involves dismantling the vertical axis. Preventatively changing the seal before it completely fails avoids costly emergency interventions at sea and protects significant investments in gearbox repairs.

Equivalent manufacturer part numbers