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New Yamaha F200–F300 4-Stroke (2014–2021) Replacement Lower Unit | Aftermarket | Standard Rotation | Fits 30″ Shaft | 1.75 Gear Ratio | 3-Year Warranty

Q: Which Yamaha outboard models does the SEI 90-423 lower unit fit?

The SEI 90-423 fits Yamaha F250UCA, F300UCA, and F300BETU 4-Stroke outboards (2014–2021) with a 30” single-piece driveshaft.

Q: What is the gear ratio of this lower unit and why is it important?

It features a 1.75:1 gear ratio optimized for torque and speed balance essential to maintain engine and propeller performance.

Q: Is this lower unit compatible with two-piece driveshaft or TERE models?

No, it is only compatible with single-piece driveshaft models and not suitable for two-piece or TERE systems.

Q: Does the SEI 90-423 lower unit come ready to install?

Yes, it arrives fully assembled, pre-filled with premium gear lube, and painted black with a customizable surface for easy installation.

Q: What warranty coverage is provided with this Yamaha F200–F300 aftermarket lower unit?

The 3-Year Fault-Free Warranty covers defects and failures under normal recreational use, ensuring long-term reliability.

Original price was: $1,921.90.Current price is: $1,699.00.

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SKU: ST-90-423-B30F Categories: Yamaha, Engine & Parts, Standard, Yamaha Lower Unit

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Description
Additional information

Description

Upgrade your Yamaha outboard’s performance and reliability with the SEI 90-423 Aftermarket Lower Unit, engineered as a direct-fit replacement for Yamaha F200–F300 4-Stroke models (2014–2021).
This fully assembled gearcase delivers OEM-level performance at a fraction of the cost and includes a 1.75:1 gear ratio designed for powerful thrust and smooth acceleration.

Built for single-piece driveshaft models without TERE (Thrust Enhancing Reverse Exhaust), this lower unit is precision-machined, corrosion-resistant, and ready to install right out of the box.

Painted in sleek black and easily repaintable to match your outboard, the SEI 423 is ideal for both freshwater and saltwater applications — backed by a 3-Year Fault-Free Warranty for complete peace of mind.

Key Features

Direct-fit OEM replacement — no modifications required
Compatible with Yamaha F250 & F300 4-Stroke outboards (2014–2021)
Precision gear ratio of 1.75:1 for optimal torque and speed balance
Single-piece driveshaft only (not for two-piece or TERE models)
Fully assembled and pre-filled with premium gear lube
Durable black finish — can be repainted to match your engine
Corrosion-resistant housing for extended service life
Backed by a 3-Year Warranty for long-term reliability

Specifications

Feature	Details
Product Name	Yamaha F200–F300 4-Stroke Lower Unit
Compatible Models	F250UCA, F300UCA, F300BETU
Horsepower Range	200 HP – 300 HP
Years Supported	2014 – 2021
Gear Ratio	1.75 : 1
Shaft Length	30″
Driveshaft Type	One-piece only (not for two-piece shafts)
TERE Compatibility	Not compatible with TERE
Rotation	Standard (Right-Hand)
Paint	Black – Paintable
Warranty	3-Year Fault-Free
Condition	New – Aftermarket
OEM Replaces	6CE-45300-11-8D, 12-8D, 13-8D, 14-8D, 15-8D
Part Code / SKU	90-423-B30F
Installation	Direct Fit – No Modifications Required
Usage	Freshwater & Saltwater Compatible

Why Choose the Yamaha F200–F300 4-Stroke Lower Unit ?

Precision Fit: 100% compatible with Yamaha F250 and F300 models (2014–2021) — plug-and-play installation.
OEM-Matched Performance: Provides factory-equivalent torque, speed, and durability at an affordable price.
Built for Marine Conditions: Saltwater-ready construction resists corrosion and wear.
No Hassle, No Guesswork: Arrives fully assembled, lubricated, and ready to bolt on.
3-Year Warranty: Backed by SEI’s trusted fault-free warranty program.

Frequently Asked Questions – Yamaha F200–F300 4-Stroke Replacement Lower Unit

1. Which Yamaha outboard models does the SEI 90-423 lower unit fit?

The SEI 90-423 aftermarket lower unit is designed for Yamaha F250UCA, F300UCA, and F300BETU 4-Stroke outboards manufactured between 2014 and 2021. It fits models with a single-piece driveshaft and a 30″ shaft length, providing a direct-fit replacement for these engines.

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

The SEI 90-423 has a 1.75:1 gear ratio designed for optimal torque and speed balance on Yamaha F200–F300 4-Stroke models. Matching gear ratio is essential to maintain propeller efficiency, engine performance, and ensuring smooth acceleration.

3. Is this lower unit compatible with two-piece driveshaft or TERE models?

No, the SEI 90-423 lower unit is compatible only with single-piece driveshaft Yamaha outboards. It is not designed for two-piece driven models or those equipped with TERE (Thrust Enhancing Reverse Exhaust) systems.

4. Does the SEI 90-423 lower unit come ready to install?

Yes, this lower unit arrives fully assembled and pre-filled with premium gear lube, ready for direct installation with no modifications required. It is painted black with a paintable surface to enable customization matching your outboard engine.

5. What warranty coverage is provided with this Yamaha F200–F300 aftermarket lower unit?

The SEI 90-423 comes with a 3-Year Fault-Free Warranty, covering defects in materials and workmanship as well as mechanical failures under normal recreational use. This warranty offers long-term reliability and peace of mind.

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.