Yamaha Piston 1 O/S 0.25 – 6H4-11635-01-00

OEM Oversized Piston for Yamaha Outboard Engine Rebuilds

The Yamaha - Piston 1 o/s 0.25 - 6H4-11635-01-00 is an original oversized piston (0.25mm over standard) designed for precision engine rebuilds. Whether you’re restoring performance after cylinder wear or addressing damage, this factory-crafted piston ensures a reliable fit and optimal combustion inside Yamaha outboard engines.

Engineered to Yamaha’s exact tolerances, it supports long-term durability and smooth power delivery on the water.

Key Features

0.25mm Oversized Fit

Ideal for use when cylinder walls have been honed or rebored beyond standard dimensions.

Genuine Yamaha Part

Ensures factory-grade quality, material specs, and tolerances.

Designed for Peak Performance

Promotes efficient compression and consistent combustion.

Compatibility

Part Number: 6H4-11635-01-00

Fits select Yamaha outboard motors requiring a 0.25mm oversized piston

Confirm engine fitment using your Yamaha model’s service manual or parts catalog.

Ideal Use Cases

Engine Rebuilds After Wear

Perfect when cylinder measurements exceed standard spec and require an O/S piston.

Performance Restoration

Supports fuel economy, compression, and reliable operation in aging motors.

Long-Term Maintenance

OEM piston helps prevent engine damage from poor aftermarket alternatives.

Why Oversized Piston Quality Matters

When you're rebuilding your outboard engine, the integrity of each internal part makes a major difference. The Yamaha - Piston 1 o/s 0.25 - 6H4-11635-01-00 provides the precise dimensions and strength needed to restore original performance while maintaining Yamaha’s renowned reliability. It’s a critical upgrade when your engine block has been machined.

Frequently Asked Questions

What does “1 o/s 0.25” mean for this piston?

It means the piston is 0.25mm larger in diameter than the standard size—designed for use in rebored or honed cylinders.

Can I install this piston in any Yamaha outboard?

It must match specific models that require the 6H4-11635-01-00 part. Always check your model’s parts manual for fitment.

Should I replace anything else when installing a new piston?

Yes. It’s strongly recommended to replace piston rings, gaskets, and inspect connecting rods and bearings during installation to ensure full performance restoration.