Mercury FourStroke 2.5, Service Manual, Page: 151 / 205

Gear Housing
Page 6A-10 90-8M0065421 NOVEMBER 2012
General Service Recommendations
There may be more than one way to disassemble or reassemble a particular part. It is recommended that the entire procedure
be read prior to repair.
IMPORTANT: Read the following before attempting any repairs.
Disassembly of a subassembly 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
to find the 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 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 the air line.
Bearings
Upon disassembly of the gear housing, all bearings must be cleaned and inspected. Clean the 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 the bearing with
compressed air, as this may cause the bearing to score from lack of lubrication. After cleaning, lubricate the bearings with High
Performance Gear Lubricant. Do not lubricate the tapered bearing cups until after inspection.
Inspect all bearings for roughness, catches, and bearing race side wear. Work the inner bearing race in and out, while holding
the outer race, to check for side wear.
When inspecting the tapered bearings, determine the condition of the rollers and the inner bearing race by inspecting the
bearing cup for pits, scoring, grooves, uneven wear, imbedded particles, and/or discoloration from overheating. Always replace
the tapered bearing and race as a set.
Inspect the gear housing for bearing races that have spun in their respective bores. If the race has spun, the gear housing must
be replaced.
Roller bearing condition is determined by inspecting the bearing surface of the shaft that the roller bearing supports. Check the
shaft surface for pits, 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 their location during disassembly to aid in reassembly. Be sure to follow the shimming
instructions during reassembly, as gears must be installed to the 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 Threadlocker to the outer diameter of all metal case oil seals. When using Loctite on seals or
threads, the 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 the l.D. of oil seals.
Draining and Inspecting the Gear Housing Lubricant
!
WARNING
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.
1. With the gear housing in the normal running position, place a clean pan under the housing and remove the oil fill screw
with its gasket. Remove the oil level screw with its gasket.
2. Inspect the gear lubricant for metal particles (lubricant will have a metal flake appearance). The presence of metal flakes
indicates the need for gear housing disassembly and component inspection.
NOTE: When draining the gearcase for the first time, the lubricant may appear cream colored due to the mixing of the
assembly lubricant and gear lubricant. This is not an indication of water intrusion. If, during subsequent draining of the
gearcase, the lubricant appears cream colored or milky, water may be present. The gearcase should be disassembled and
all gaskets, seals and O‑rings replaced. Inspect all components for water damage.