This SEI Marine Upper Gear Set is a precision-engineered replacement for MerCruiser Type I, R, MR, and Alpha One sterndrives used with 3.0L 4-cylinder engines (1972–1990).
Featuring a 1.94 / 2.40 gear ratio, this set ensures smooth, quiet operation and efficient power transfer throughout the upper gear housing.
It replaces OEM 43-55778A3 and is also compatible with Gen II drives (Serial #0K999999 and below).
Manufactured to strict OEM specifications, SEI gear sets are built for reliability, durability, and performance — backed by a 3-Year Fault-Free Warranty.
Product Features
- Direct OEM Replacement: Replaces MerCruiser OE# 43-55778A3
- Fitment: MerCruiser Type I, R, MR, and Alpha One drives (1972–1990)
- Additional Fitment: Gen II drives (Serial #0K999999 and below)
- Engine Compatibility: 3.0L 4-cylinder models
- Gear Ratio: 1.94 / 2.40
- Condition: 100% brand-new SEI Marine replacement gear set
- Warranty: 3-Year Fault-Free Warranty provided by SEI Marine
Additional Information
Note: Designed for 3.0L 4-cylinder MerCruiser engines and compatible Alpha One / Gen II upper gear housings.
If you need matching lower gear components or related hardware, please email or fill out the contact form and we’ll help locate the correct parts for your setup.
Shipping Information
SHIPPING: Additional shipping fees to Alaska, Hawaii, U.S. Territories, or international destinations will be calculated after checkout.
You will receive an email and a PayPal money request for the additional shipping charges at the email address provided.
(Some items are excluded from international shipping.)
Customer Support
For questions or to confirm compatibility, please email customerservice@marinepartswarehouse.com .
Please include your engine model number to help confirm proper fitment before ordering.
