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New Yamaha 250HP 4-Stroke (2005–2018) Replacement Lower Unit | Aftermarket | Standard Rotation | Fits 20″, 25″ & 30″ Shafts | 3-Year Warranty

Name: New Yamaha 250HP 4-Stroke (2005–2018) Replacement Lower Unit | Aftermarket | Standard Rotation | Fits 20″, 25″ &amp; 30″ Shafts | 3-Year Warranty
Brand: Yamaha
SKU: ST-90-422
Availability: InStock
Rating: 3.78 (9 reviews)

Original price was: $1,572.25.Current price is: $1,399.00.

Rated 3.78 out of 5 based on 9 customer ratings

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SKU: ST-90-422 Category: Counter Rotation

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Description
Additional information

Description

Upgrade your Yamaha 250HP outboard with this SEI 90-422 Aftermarket Lower Unit, engineered as a direct-fit replacement for Yamaha F250 4-Stroke engines (2005–2018).
This high-quality gearcase delivers OEM-level performance and reliability at a fraction of the cost — no modifications required.

Built for durability and long service life, the unit features a water-cooled bearing carrier, dual and side water intakes, and a standard (right-hand) rotation design for optimal cooling and smooth operation in all water conditions.
Each unit comes pre-painted in black and can be easily repainted to match your outboard.

Available in 20″, 25″, and 30″ shaft lengths, this lower unit is ideal for restoring top-end performance and maintaining reliability for both freshwater and saltwater use.

Specifications

Feature	Details
Compatible Engines	Yamaha 4-Stroke F250 & select F225 models
Horsepower	250 HP
Rotation	Standard (Right-Hand)
Gear Ratio	2.00 : 1
Shaft Lengths	20″, 25″, 30″
Water Intake	Dual & Side (Replaces both versions)
Bearing Carrier	Water-cooled
Finish	Black (Repaintable to match engine)
Years Covered	2005 – 2018
Condition	New – Aftermarket
Warranty	3-Year Fault-Free Warranty
Part Numbers	90-422-B20F (20″), 90-422-B25F (25″), 90-422-B30F (30″)

Why Choose the Yamaha 250HP 4-Stroke Lower Unit (SEI 90-422)?

Direct OEM Replacement: Designed to precisely fit Yamaha F250 and select F225 4-Stroke outboards (2005–2018) — no modifications required.
High-Performance Engineering: Built to deliver smooth, quiet, and reliable operation comparable to Yamaha factory units.
Dual & Side Water Intakes: Ensures superior cooling performance, even in shallow or high-temperature waters.
Water-Cooled Bearing Carrier: Extends the life of internal components under heavy-duty marine use.
Fully Assembled & Ready to Install: Arrives pre-filled with premium gear lube for quick setup.
Repaintable Black Finish: Can be customized to match your outboard’s original color.
3-Year Warranty: Comprehensive coverage for peace of mind and long-term reliability.

Frequently Asked Questions – Yamaha 250HP 4-Stroke Replacement Lower Unit

1. Which Yamaha outboard models are compatible with the SEI 90-422 replacement lower unit?

The SEI 90-422 replacement lower unit is designed to fit Yamaha F250 4-Stroke outboards and select F225 models manufactured between 2005 and 2018. It supports multiple shaft lengths: 20″, 25″, and 30″, offering a direct-fit, no-modification solution for these engine types.

2. What is the gear ratio for this lower unit and why is it important?

This replacement lower unit features a 2.00:1 gear ratio, which matches the OEM specification for Yamaha F250 and compatible F225 models. Matching the gear ratio is critical to maintaining proper propeller performance, engine efficiency, and preventing premature wear.

3. What features does this SEI 90-422 lower unit offer for durability and performance?

The unit includes a water-cooled bearing carrier to extend component life, dual and side water intakes for superior cooling efficiency, and is constructed with OEM-level precision for smooth, quiet operation. Its black paintable finish allows easy customization to match your outboard.

4. Is this unit ready to install out of the box, or does it require additional preparation?

The SEI 90-422 arrives fully assembled and pre-filled with premium marine gear lube, making installation quick and hassle-free. It requires no modifications or additional setup beyond aligning shaft length and gear ratio compatibility with your existing engine.

5. What warranty protection comes with the SEI 90-422 Yamaha 250HP lower unit?

This aftermarket lower unit is backed by a 3-year fault-free warranty, covering defects in materials and workmanship as well as mechanical failures under normal recreational use, providing confidence and peace of mind for marine enthusiasts.

Looking for other models or gear ratios?
Browse all Yamaha Lower Units here — find compatible options for 40HP, 60HP, 115HP, 150HP, and more Yamaha outboards.

Additional information