Mercury – Standard Rotation Gearcase | MerCruiser R/MR/Alpha One | Low-Copper Alloy & Tri-Paint Finish | 8951A43

Overview
If you’ve spent enough time piloting a sterndrive boat, you know how much the lower unit shapes the feel of every trip. The way the boat lifts, how it holds in a turn, the steady pull when you push up onto plane—all of it starts in the gearcase. When the gearcase is strong and healthy, everything about the boat feels tighter, smoother, and more predictable. This Mercury Marine part brings that sense of control back, giving your MerCruiser sterndrive the power and confidence it was built for, whether you’re cruising across open water or easing through a busy channel.

Key Features
• Standard rotation (right-hand) gearcase for MerCruiser R, MR, and Alpha One sterndrives.
• Built with XK360 low-copper alloy for enhanced corrosion resistance.
• Protected with Mercury’s durable Tri-Paint anti-corrosion coating.
• Features spiral-cut steel bevel gears for smooth, quiet operation.
• Engineered to match original Mercury Marine part number specifications.

Engine & Boat Compatibility
• Fits MerCruiser R, MR, and Alpha One sterndrives.
• Common on sport boats, bowriders, small cruisers, runabouts, and family boats.
• Suitable for both saltwater and freshwater applications.

Performance & Practical Benefits
A well-built gearcase changes everything about how a sterndrive handles. This unit’s spiral-cut gears mesh smoothly, reducing vibration and giving your boat a quiet, confident feel—even when you push it hard. You’ll notice improved handling in tight turns, steadier lift during acceleration, and better thrust in rougher seas.

The XK360 low-copper alloy provides excellent corrosion resistance, especially important for boats that spend long stretches in brackish or saltwater. The Tri-Paint finish adds another barrier of protection, helping the gearcase hold its clean, sharp look while preventing the kind of long-term wear that can compromise performance. Internally, the gears and shafts are engineered with the same tolerances Mercury uses on factory units, so installation feels natural and precise.

A good gearcase doesn’t just move your boat—it inspires trust. With this one, you’ll feel that tight, secure control that makes every outing more enjoyable.

Why Buy OEM
Gearcases carry enormous stress, and even small deviations in machining or metallurgy can lead to vibration, early wear, or catastrophic failure. Aftermarket units may look similar, but they rarely meet Mercury’s standards for alloy strength, gear precision, or hydrodynamic design.

A genuine Mercury Marine part ensures proper alignment, exact gear ratios, and long-term durability. It installs cleanly, performs flawlessly, and protects your investment in ways cheaper alternatives simply can’t. It’s the kind of upgrade or replacement you choose when you want absolute confidence in your sterndrive.

FAQ

Q1: Which engines does this gearcase fit?
It fits MerCruiser R, MR, and Alpha One sterndrives.

Q2: What makes it different from aftermarket gearcases?
It uses Mercury’s low-copper alloy, Tri-Paint protection, and precision-machined gears for smooth, long-lasting performance.

Q3: How do I confirm it’s the right replacement?
Check your sterndrive model and parts listing. If you see part number 8951A43, this is the correct unit.

Q4: Can it be used in both saltwater and freshwater?
Yes. The low-copper alloy and Tri-Paint finish provide excellent corrosion resistance.

Q5: Is installation straightforward?
Most marine technicians find the installation clean and simple thanks to the precise OEM fit.