Mercury – Cylinder Bore Seal | High-Performance Outboards | Precision Composite | 884391

Overview

There’s a certain comfort that settles in when your engine fires up without a hiccup — that deep, steady confidence only boaters understand. When you’re pushing a powerful outboard hard, whether you’re chasing early-morning redfish or running upriver with the family, you want every internal seal pulling its weight. The Mercury Marine part number 884391 Cylinder Bore Seal feels like one of those quiet heroes inside the engine, doing its job without ever calling attention to itself. You may not see it, but you’ll notice the difference it makes in how smoothly your motor breathes and how reliably it responds when you lean on the throttle.

Key Features

• Helps maintain a clean, tight seal inside the cylinder bore for consistent engine performance
• Precision-formed composite material built for demanding outboard conditions
• Designed for select Mercury and Mariner 200–300 horsepower FourStroke and two-stroke engines
• Compatible with DFI, EFI, Sport XS, Pro XS, and select 250 horsepower JetDrive SportJet models
• Crafted for reliable fitment and confident installation with common tools

Engine & Boat Compatibility

• Compatible with Mercury and Mariner 200–300 horsepower outboards
• Works with FourStroke, two-stroke, DFI, EFI, Sport XS, and Pro XS engines
• Fits select 250 horsepower JetDrive SportJet applications
• Common on bass boats, offshore center consoles, bay boats, performance skiffs, pontoons, and freshwater fishing rigs

Performance & Practical Benefits

When a cylinder bore seal is fresh and properly seated, you can feel it in the engine’s character. Throttle response stays crisp instead of lazy. Idle feels steady instead of wandering. Acceleration has that clean, confident push instead of a hesitant climb. The 884391 seal helps keep combustion pressure exactly where it belongs, supporting smooth performance across the whole powerband.

Durability plays a big role here too. Engines in the 200–300 horsepower range put real stress on their internal components. Heat builds, pressure changes constantly, and the engine loads can shift with every swell or turn. This Mercury Marine part is designed to stay tight, remain stable under all that stress, and continue sealing cleanly season after season. It’s the kind of part you install once and trust — no second-guessing, no chasing symptoms later. And because the fit is so clean, installation feels straightforward even for boaters who prefer handling some of their own maintenance.

Why Buy OEM

If you’ve ever swapped out a bargain-brand seal only to redo the job a few months later, you know why genuine parts matter. Mercury builds its components with the same mindset that keeps their engines running strong for decades. Exact tolerances. Matching materials. Engineering meant for real-world use, not just the packaging. When you choose an original Mercury Marine part, you’re choosing a seal that seats right, stays tight, and protects an engine that probably costs more than your first car. It’s the smart choice if you care about longevity, reliability, and avoiding avoidable headaches.

FAQ

Q1: Which Mercury engines does the Cylinder Bore Seal fit?

It fits select Mercury and Mariner 200–300 horsepower engines, including FourStroke, two-stroke, DFI, EFI, Sport XS, Pro XS, and certain 250 horsepower JetDrive SportJets.

Q2: What makes this different from aftermarket options?

The precision. Mercury manufactures it to match exact factory tolerances, which helps it seal better and last longer.

Q3: How do I know if this is the correct replacement?

Check your engine’s model and serial information. If you fall within the listed horsepower and engine families, this part number is usually the right match.

Q4: Can it be used in saltwater and freshwater?

Yes — the materials hold up well in both environments as long as standard maintenance is followed.

Q5: Is installation straightforward?

For most boat owners with a bit of mechanical comfort, yes. It installs cleanly with common shop tools.