Mercury – Cylinder Block Exhaust Plate Gasket | 2-Stroke Performance Series | Composite Gasket Material | 991764

Overview

There’s a certain kind of confidence you feel when your outboard fires up clean and strong, the way it’s supposed to. It comes from knowing every seal, every connection, every piece of your engine is working together the way the engineers intended. A good gasket may not be the most glamorous part on the motor, but when you’re running twenty miles upriver or trimming down to punch through chop, you want the kind of quiet reliability that never makes you second-guess your setup. That’s why boaters stick with genuine Mercury Marine parts like the 991764 Cylinder Block Exhaust Plate Gasket—because dependable performance starts with the pieces you don’t always see.

Key Features

• Designed to seal the cylinder block exhaust plate on select high-output Mercury and Mariner 2-stroke engines
• Constructed with a durable composite gasket material engineered for high heat and exhaust pressure
• Precision-cut for a tight, secure fit that maintains proper exhaust flow and prevents leaks
• Manufactured to Mercury Marine specifications for long-term reliability under demanding on-water conditions
• Straightforward installation with common shop tools

Engine & Boat Compatibility

• Fits select Mercury and Mariner 105–220 horsepower 2-stroke outboards
• Compatible with 2.5-liter Laser, EFI, DFI, Jet, Pro XS, XR-6, Magnum II and III, MAG, XRI, and XR-4 models
• Common on performance hulls, bass boats, river jet boats, center consoles, and older high-output fishing rigs
• Designed for engines where a multi-point exhaust plate seal is required to maintain proper combustion and cooling balance

Performance & Practical Benefits

On the water, little things make a big difference. A gasket like this might seem simple, but the seal it provides keeps your engine running tight, smooth, and predictable. By preventing exhaust leaks, it helps maintain steady performance across the powerband—you’ll feel cleaner acceleration, more consistent idle, and a healthier overall temperature balance throughout the block.

You’ll also notice the peace of mind that comes with a properly sealed exhaust plate. No hot gases escaping where they shouldn’t, no stray leaks creating erratic performance, and no unexpected maintenance surprises down the line. The fit is snug and secure, giving you the kind of quiet reassurance that lets you focus on the water, not the motor. With the 991764 gasket in place, upkeep stays simple: inspect during routine service, replace as needed, and enjoy a longer, more reliable life from your engine.

Why Buy OEM

Ask any seasoned boater, and they’ll tell you that a gasket is one part you don’t want to gamble on. A genuine Mercury Marine part like 991764 is built specifically for these high-performance 2-stroke engines, using materials that match factory heat tolerance, compression pressures, and precise dimensions. Aftermarket versions may look similar, but they often fall short when it comes to long-term sealing and exact fit. OEM keeps things simple—you install it once, and it works the way it’s supposed to. It’s the smart, practical choice for anyone who wants their engine to perform right the first time.

FAQ

Q1: Which engines does the Cylinder Block Exhaust Plate Gasket part number 991764 fit?

It fits select Mercury and Mariner 105–220 horsepower 2-stroke outboards, including Laser, EFI, DFI, Jet, Pro XS, XR-6, Magnum II and III, XRI, MAG, and XR-4 models.

Q2: What makes this part different from aftermarket options?

It’s engineered to Mercury Marine standards, ensuring proper sealing under high heat and pressure for long-term reliability.

Q3: How do I know if it matches my motor?

Check your service manual or parts list to confirm compatibility with your specific outboard model and serial range.

Q4: Can it be used in both freshwater and saltwater?

Yes—its composite construction performs reliably in either environment.

Q5: Is installation straightforward?

Yes. Most boat owners can install it with basic tools and standard service-manual guidance.