Lower Unit Gearcase – Fits Yamaha V4 115HP & 130HP 2-Stroke Outboards (Replaces 602-90-405-A20)
Lower Unit Gearcase – Fits Yamaha V4 115HP & 130HP 2-Stroke Outboards (Replaces 602-90-405-A20) is backordered and will ship as soon as it is back in stock.
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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.
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Lower Unit Gearcase – Fits Yamaha V4 115HP & 130HP 2-Stroke Out...
Lower Unit Gearcase – Fits Yamaha V4 115HP & 130HP 2-Stroke Outboards (Replaces 602-90-405-A20) is backordered and will ship as soon as it is back in stock.
Product Details
This Lower Unit Gearcase – Fits Yamaha V4 115HP & 130HP 2-Stroke Outboards is an aftermarket solution designed for Yamaha V4 115HP and 130HP 2-stroke engines requiring a 20" shaft, standard right-hand rotation, and a 2:1 gear ratio. It offers a reliable, direct-fit replacement to get your outboard back in service.
It directly cross-references with SEI part number 602-90-405-A20.
- Engineered for direct bolt-on installation.
- Finished in durable black paint.
- Exclusively compatible with 2-Stroke engine applications.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| SEI | 602-90-405-A20 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
| Brand | Model | Rated HP | Stroke | Notes |
|---|---|---|---|---|
| Yamaha | V4 | 115 | 2-Stroke | Standard rotation only |
| Yamaha | V4 | 130 | 2-Stroke | Standard rotation only |
Technical Specs
- Product Type
- Replacement Lower Unit Gearcase
- Installation
- Direct bolt-on replacement
- Gear Ratio
- 2:1
- Rotation
- Standard (Right-Hand)
- Shaft Length
- 20" (508 mm)
- Housing Color
- Black
- Application
- 2-Stroke engines only
- Other Technical Attributes
- Will not work on 4-Stroke Engine applications
- Product Dimensions
- 114.0 x 22.0 x 70.5 cm
What’s in the Box
- 1 x Complete Lower Unit Gearcase Assembly (602-90-405-A20)
Installation Notes
- Disconnect the battery and spark plug wires for safety.
- Place a drain pan under the lower unit and remove the gear oil drain and vent screws to empty the oil.
- Remove the bolts securing the lower unit to the outboard's midsection.
- Carefully lower the old gearcase, ensuring the shift shaft linkage is disconnected.
- Clean the mating surfaces on the engine leg and install a new water pump housing base gasket.
- Align the driveshaft, water tube, and shift shaft, then raise the new gearcase into position.
- Install and tighten the mounting bolts to the manufacturer's recommended torque specifications.
- Reconnect the shift shaft linkage and confirm proper gear engagement (Forward-Neutral-Reverse).
- Refill the gearcase with fresh, high-quality marine gear lubricant according to the manufacturer's procedure. Install new drain screw gaskets and tighten screws securely.
Troubleshooting & FAQ
How do I confirm this fits my specific engine model and year?
This lower unit is designed for Yamaha V4 115HP & 130HP 2-Stroke outboards with a 20" shaft. The most reliable method is to compare the specifications (gear ratio, shaft length, rotation) and visual details in the product photos with your existing lower unit. If any specification differs, do not purchase.
Will this work on my 4-Stroke Yamaha engine?
No. This lower unit is explicitly designed for 2-Stroke engine applications only and is not compatible with any 4-Stroke models.
What are the signs that my current lower unit is failing?
Common symptoms include metallic grinding or clunking noises, difficulty shifting gears, visible metal shavings in the gear oil (a "milky" appearance also indicates water intrusion), or vibrations felt through the hull during operation. If you notice any of these signs, inspection is recommended.
What maintenance is required for this lower unit?
Regularly inspect and change the gear oil at least once per season or every 100 hours of use, whichever comes first. Use a high-quality marine gear lubricant specified for your outboard. Always check for water intrusion (milky oil), which indicates a seal failure that must be addressed immediately.
OEM vs. Aftermarket?
This listing is an aftermarket replacement (not OEM). Built to OEM-level specifications with comparable materials. Manufactured in an ISO 9001 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
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