Mercury Quicksilver Propeller Shaft Thrust Washer 18448 – Counter-Rotation Gearcase

Overview

Part Number: 18448 (service format: 12-18448)
Brand: Mercury / Quicksilver
Official Product Type: Propeller Shaft Thrust Washer
Supersedes: No confirmed superseded part number
GTIN: 745061123717
System: Counter-Rotation Gearcase — Propeller Shaft Thrust Stack

The Mercury Quicksilver 18448 is a genuine OEM internal propeller-shaft thrust washer for selected Mercury and Mariner counter-rotation gear housings. It forms part of the propeller-shaft thrust stack inside the lower unit, working alongside the thrust bearing (31-15842), thrust race (8182911), and keeper (814605) to carry axial load on the propeller shaft. Mercury parts diagrams commonly show two 18448 washers per assembly. This is an internal gearcase component — it is not the large external thrust washer that sits behind the propeller.

Key Features

• Genuine Mercury Marine / Quicksilver OEM propeller-shaft thrust washer
• Internal gearcase component — part of the propeller-shaft thrust stack
• Used with thrust bearing 31-15842, thrust race 8182911, and keeper 814605
• Mercury diagrams commonly specify 2 washers per counter-rotation assembly
• GTIN: 745061123717

Compatible Applications

• Mercury / Mariner 135 HP counter-rotation gearcase (selected serial ranges)
• Mercury / Mariner 150 HP counter-rotation gearcase (selected serial ranges)
• Mercury / Mariner 175 HP counter-rotation gearcase (selected serial ranges)
• Mercury / Mariner 200 HP counter-rotation gearcase (selected serial ranges)
• Mercury / Mariner 225 HP DFI counter-rotation gearcase (selected serial ranges)
• Selected Mercury 2.5L and 3.0L counter-rotation outboard gear housings
• Examples: V-135 DFI 2.5L, V-175, 200 3.0L DFI DTS, 225 DFI counter-rotation propeller-shaft assemblies

Serial Number Fitment Notice

Fitment must be confirmed by exact engine model, serial number, and the counter-rotation gear housing / propeller-shaft parts diagram. This is an internal gearcase thrust washer — do not confuse it with the larger external thrust washer positioned behind the propeller. Always confirm using the applicable Mercury parts diagram before ordering.

Dimensions & Weight

• Weight: Approx. 0.02 lb (0.009 kg) per washer
• Packed dimensions: Approx. 5.7 cm × 5.7 cm × 0.6 cm (2.25 × 2.25 × 0.25 in)

When to Replace

Replace this washer during gearcase overhaul if it shows scoring, grooving, heat discoloration, distortion, or abnormal wear. Inspect the washer whenever the adjoining thrust bearing (31-15842) or thrust race (8182911) is being replaced — the full thrust stack should be evaluated together.

Service Interval

Inspect at every gearcase rebuild or lower unit reseal service. There is no fixed hour-based replacement interval — condition-based inspection during service is the standard practice for internal thrust components.

Installation Notes

• The 18448 washer is used in conjunction with: thrust bearing 31-15842, thrust race 8182911, and keeper 814605
• Mercury diagrams show these parts installed as matched components within the counter-rotation propeller-shaft assembly
• Correct assembly order and gearcase setup are critical during reassembly
• Do not substitute with a generic washer — OEM thickness and surface finish directly affect thrust clearance and axial load distribution inside the gearcase
• Confirm quantity required per your specific assembly diagram — typically 2 per assembly

Related Parts

• Mercury Outboard Roller Bearing Counter-Rotation Gear Housing 15841 — related counter-rotation bearing component
• Thrust bearing: 31-15842 (sold separately)
• Thrust race: 8182911 (sold separately)
• Keeper: 814605 (sold separately)

Alternate / Related Part Numbers

• Current: 18448 / 12-18448
• Related thrust bearing: 31-15842
• Related thrust race: 8182911
• Related keeper: 814605

Technical FAQ

Q: Is this the same washer as the one that sits behind the propeller?
A: No. The 18448 is an internal thrust washer located inside the gearcase within the propeller-shaft bearing stack. The external thrust washer behind the propeller is a separate part. Confirm which component your application requires before ordering.

Q: How many washers does my gearcase need?
A: Mercury parts diagrams for applicable counter-rotation assemblies commonly show 2 thrust washers (18448) per gearcase. Always verify the quantity on your specific assembly diagram before ordering.

Q: Can I replace just the washer without replacing the thrust bearing and race?
A: If the washer is the only worn component, replacing it alone is acceptable. However, because the washer, bearing, and race work together as a matched stack, Mercury recommends inspecting all three whenever any one is being replaced. Replacing worn stack components together avoids a second teardown.

Parts Desk Insight

The most common ordering confusion with this part is customers mistaking it for the external prop thrust washer. The 18448 is strictly an internal gearcase component. Fitment is best confirmed by the counter-rotation gearcase diagram rather than engine horsepower alone — the washer thickness and fit matter because they directly affect thrust clearance inside the lower unit. At rebuild time, replacing the full thrust stack (washer, bearing, race) together is inexpensive compared to a repeat teardown if a worn adjacent component causes early failure.