Mercury – Timing Belt | 9.9–20hp EFI Series | Marine-Grade Polymer | 8M0135591

Overview

Anyone who spends time on the water knows that the smallest parts can make the biggest difference. A timing belt isn’t something you admire or talk about at the dock, but you definitely feel the confidence it gives when it’s doing its job right. With the Mercury Marine part 8M0135591 Timing Belt, you get that quiet reassurance every time the engine fires up. Whether you’re easing out from the slip at dawn or pushing across a windy bay, it’s one less thing you’ll worry about — because you know your motor is running in sync, smooth and steady.

Key Features

• Designed for Mercury 9.9–20hp EFI outboards
• Fits serial numbers 0R833820 and above (2017 and newer)
• High-strength polymer belt engineered for precise timing
• Durable construction for extended service life
• Manufactured to exact Mercury Marine specifications
• Reliable performance under both low-speed maneuvering and full-throttle operation

Engine & Boat Compatibility

• Mercury 9.9hp EFI
• Mercury 15hp EFI
• Mercury 20hp EFI
• Ideal for small fishing boats, utility skiffs, aluminum jon boats, tenders, inflatables, and lightweight runabouts

Performance & Practical Benefits

A timing belt is the heartbeat of an EFI outboard’s internal rhythm. When it’s in perfect condition, the engine feels different — tighter, more responsive, and far more predictable. The Mercury 8M0135591 belt is built to maintain that exact synchronization, helping your motor breathe correctly and burn fuel efficiently. You’ll notice smooth acceleration, cleaner idle, and less mechanical strain across the powerband.

For boaters who service their own engines, this belt installs with a clean, positive fit that’s unmistakably OEM. There’s no stretchiness, no rough edges, nothing that feels “close enough.” It’s precise, and that precision pays off when you’re on the water far from the ramp. Mercury engineered it to withstand heat, vibration, salt exposure, and sudden load changes — all the things small outboards experience in a typical season.

The real benefit? Peace of mind. A dependable timing belt means fewer surprises, more reliable performance, and an engine that stays in sync no matter how you use it.

Why Buy OEM

Timing components aren’t the place to experiment with aftermarket options. Mercury designs these belts specifically around the timing system of their EFI engines — exact tooth shape, exact length, exact tension. That’s why OEM belts tend to run smoother, last longer, and protect other engine components better. When you choose an original Mercury Marine part, you’re investing in reliability, efficiency, and long-term performance you can feel every time you head out.

FAQ

Q1: Which engines does the 8M0135591 timing belt fit?

It fits Mercury 9.9–20hp EFI outboards with serial numbers 0R833820 and newer.

Q2: How is this belt different from aftermarket versions?

Mercury’s belt matches factory tolerances exactly, ensuring the proper timing and long-term durability that generic belts often can’t provide.

Q3: How do I confirm this is the right replacement?

Check your engine’s serial number. If it falls within the listed range, this is the correct OEM belt.

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

Absolutely. It’s engineered for harsh marine environments and holds up well in both conditions.

Q5: Is installation manageable for most boat owners?

Yes, for those familiar with basic outboard service. Mercury provides clear guidance in the owner’s and service manual.