General Service Recommendations; Shims; Seals; Draining And Inspecting Gear Housing Lubricant - Mercury 25 EFI Service Manual

Gear Housing

General Service Recommendations

There may be more than one way to disassemble or reassemble a particular part, therefore, it is recommended that the entire
procedure be read prior to repair.
IMPORTANT: Read the following before attempting any repairs.
In many cases, disassembly of a sub‑assembly may not be necessary, until cleaning and inspection reveals that disassembly is
required for replacement of one or more components.
Service procedure order in this section is a normal disassembly/reassembly sequence. It is suggested that the sequence be
followed without deviation to assure proper repairs. When performing partial repairs, follow the instructions to the point where
the desired component can be replaced, then proceed to reassembly and installation of that component in the reassembly part
of this section. Use the Table of Contents (on back of section divider) to find correct page number.
Threaded parts are right hand (RH), unless otherwise indicated.
When holding, pressing, or driving is required, use soft metal vise jaw protectors or wood for protection of parts. Use a suitable
mandrel (one that will contact only the bearing race) when pressing or driving bearings.
Whenever compressed air is used to dry a part, verify that no water is present in air line.
Bearings
Upon disassembly of gear housing, all bearings must be cleaned and inspected. Clean bearings with solvent and dry with
compressed air. Air should be directed at the bearing so that it passes through the bearing. Do not spin bearing with
compressed air, as this may cause bearing to score from lack of lubrication. After cleaning, lubricate bearings with Premium
Gear Lubricant. Do not lubricate tapered bearing cups until after inspection.
Inspect all bearings for roughness, catches, and bearing race side wear. Work inner bearing race in and out, while holding
outer race, to check for side wear.
When inspecting tapered bearings, determine condition of rollers and inner bearing race by inspecting bearing cup for pitting,
scoring, grooves, uneven wear, imbedded particles, and/or discoloration from overheating. Always replace tapered bearing and
race as a set.
Inspect gear housing for bearing races that have spun in their respective bores. If race has spun, gear housing must be
replaced.
Roller bearing condition is determined by inspecting the bearing surface of the shaft that the roller bearing supports. Check
shaft surface for pitting, scoring, grooves, imbedded particles, uneven wear, and/or discoloration from overheating. The shaft
and bearing must be replaced, if the conditions described are found.

Shims

Keep a record of all shim amounts and location during disassembly to aid in reassembly. Be sure to follow shimming
instructions during reassembly, as gears must be installed to correct depth and have the correct amount of backlash to avoid
noisy operation and premature gear failure.

Seals

As a normal procedure, all O‑rings and oil seals should be replaced without regard to appearance. To prevent leakage around
oil seals, apply Loctite 271 to outer diameter of all metal case oil seals. When using Loctite on seals or threads, surfaces must
be clean and dry. To ease installation, apply 2‑4‑C with PTFE on all O‑rings. To prevent wear, apply 2‑4‑C with PTFE on l.D. of
oil seals.

Draining and Inspecting Gear Housing Lubricant

Rotating propellers can cause serious injury or death. Never operate the boat out of the water with a propeller installed.
Before installing or removing a propeller, place the drive unit in neutral and engage the lanyard stop switch to prevent the
engine from starting. Place a block of wood between the propeller blade and the anti‑ventilation plate.
Page 6A-10
WARNING
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© 2016 Mercury Marine 90-8M0105568 eng MARCH 2016