SEI Yamaha Lower Unit 90-422-B25F – Fits Yamaha F250 Outboards with 25" Driveshaft (Replaces 6P2-45300-41-8D/43-8D)
SEI Yamaha Lower Unit 90-422-B25F – Fits Yamaha F250 Outboards with 25" Driveshaft (Replaces 6P2-45300-41-8D/43-8D) is backordered and will ship as soon as it is back in stock.
Worry-free returns
Worry-free returns
Shop with confidence. If you’re not completely satisfied, eligible items may be returned within the return window, provided they are unused and in original packaging.
If the return is due to our error or a defective item, we’ll make it right.
Please contact us before returning any item.
Delivery and Shipping
Delivery and Shipping
Orders are typically processed within 1–2 business days.
U.S. orders usually arrive within 6–15 days, depending on stock location and destination.
International delivery times may vary due to customs processing.
Tracking information will be provided once your order ships.
SEI Yamaha Lower Unit 90-422-B25F – Fits Yamaha F250 Outboards with...
SEI Yamaha Lower Unit 90-422-B25F – Fits Yamaha F250 Outboards with 25" Driveshaft (Replaces 6P2-45300-41-8D/43-8D) is backordered and will ship as soon as it is back in stock.
Product Details
This is an aftermarket SEI Yamaha Lower Unit 90-422-B25F, engineered as a complete gearcase replacement for Yamaha 4-Stroke 250 HP F-series outboards (2005–2018) that require a 25" driveshaft and a 2:1 gear ratio. It offers a reliable, cost-effective solution for restoring your engine's performance.
It serves as a direct interchange for Yamaha OEM part numbers 6P2-45300-41-8D, 6P2-45300-42-8D, and 6P2-45300-43-8D.
- Designed for direct bolt-on installation.
- Comes complete with a pre-installed water pump.
- Constructed from durable, marine-grade aluminum.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| SEI (Aftermarket) | 90-422-B25F |
| Yamaha (OEM) | 6P2-45300-41-8D |
| Yamaha (OEM) | 6P2-45300-42-8D |
| Yamaha (OEM) | 6P2-45300-43-8D |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
This lower unit is compatible with select Yamaha F250 and F225 series outboards. Please verify your specific model and year before ordering.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Yamaha | F250XA | 250 | 4-Stroke | 2012–2018 | 6P2-45300-43-8D | |
| Yamaha | F250XCA | 250 | 4-Stroke | 2017 | 6P2-45300-43-8D | |
| Yamaha | F250TXR | 250 | 4-Stroke | 2005–2011 | 6P2-45300-41-8D, 6P2-45300-42-8D | |
| Yamaha | F250BTXR | 250 | 4-Stroke | 2008–2009 | 6P2-45300-41-8D, 6P2-45300-42-8D | |
| Yamaha | F250TXRD | 250 | 4-Stroke | 2005 | 6P2-45300-41-8D | |
| Yamaha | F225TXR | 225 | 4-Stroke | 2002–2011 | 6P2-45300-41-8D, 6P2-45300-42-8D | Also fits 225 HP models |
Technical Specs
- Product Type
- Complete Lower Unit (Gearcase)
- Installation
- Direct bolt-on replacement
- Fuel Type
- Gasoline
- Connection
- Direct driveshaft spline connection
- Housing Material
- Marine-grade aluminum
- Housing Color
- Black (requires painting to match engine)
- Dimensions (H x W x L)
- 130.0 x 22.5 x 77.0 cm
- Fitting Type
- Standard rotation (right-hand)
- Water Pump
- Included, pre-installed
- Gear Ratio
- 2:1
- Shaft Length
- 25" (635 mm)
- Water Pickup
- Dual water pickup
- Warranty
- 3-Year No-Fault Warranty
- Other Technical Attributes
- Water-cooled bearing carrier
What’s in the Box
- 1 x Complete Lower Unit Assembly (90-422-B25F) with pre-installed water pump
Installation Notes
- Disconnect the battery and secure the shift linkage.
- Position a suitable container and drain the old gearcase oil completely.
- Remove the mounting bolts securing the lower unit to the engine's midsection.
- Carefully lower the old unit away from the engine, ensuring the driveshaft disengages without binding.
- Thoroughly clean the mating surfaces on the engine.
- Apply a light coat of marine-grade grease to the new unit's driveshaft and shift shaft splines.
- Carefully raise the new lower unit, aligning the driveshaft, water tube, and shift shaft.
- Install the mounting bolts and torque them to the manufacturer's specified values in the correct sequence.
- Reconnect the shift linkage and confirm smooth engagement of forward, neutral, and reverse gears.
- Fill the new gearcase with the correct type and amount of marine gear lubricant.
- Reconnect the battery. Before open water use, test the engine's operation, cooling, and shifting in a safe, controlled environment.
Troubleshooting & FAQ
How do I confirm this lower unit fits my Yamaha outboard?
Check your engine's model number and year against the compatibility chart. This unit fits specific F250 and F225 models with a 25" shaft and 2:1 gear ratio. Also, verify your OEM part number matches the replacements listed.
Do I need to paint this gearcase?
Yes. The housing is supplied in a base black color and requires painting with a marine-grade paint to color-match your specific Yamaha outboard and provide an additional layer of corrosion protection.
What are the signs my old lower unit is failing?
Common signs include metal shavings in the gear oil, a grinding or clunking noise when shifting or running, water in the oil (milky appearance), or a bent/damaged propshaft.
Does this unit include the water pump and other hardware?
Yes, a complete new water pump assembly is pre-installed for your convenience. However, mounting hardware (bolts, nuts, washers) is not typically included and you should plan to reuse your existing hardware if it is in good condition.
What gear oil should I use?
Use a high-quality marine gear lubricant that meets API GL-5 specifications, as recommended by your engine's manufacturer service manual.
Is this a standard or counter-rotation model?
This is a standard, right-hand rotation lower unit.
OEM vs. Aftermarket?
This listing is an aftermarket replacement (not OEM). Built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, batch-inspected for consistency.
Shipping speed & cost
We ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.
Warranty & returns
Covered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact support with your order details. Returns are accepted within our standard window (unused & in original condition). See our policy page or reach out for instructions.
Safety & Important Info
- Verify images/specifications vs your original part. If anything differs—even if your model appears compatible—do not purchase.
- This is an aftermarket replacement, not an OEM component.
- Professional installation is recommended for safety and performance.
About Sea Sierra
- Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
- Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
- Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.
Payment & Security
Payment methods
Your payment information is processed securely. We do not store credit card details nor have access to your credit card information.
