This Bay Manufacturing 5-inch Outboard Extension Kit provides a reliable and durable solution for increasing the shaft length of your Mercury 40–60 HP 4-stroke outboard. Ideal for improving propeller bite, reducing cavitation, and tailoring your engine to deeper-water applications, this kit converts your motor to a longer shaft using OEM-grade materials and precision components.
Each extension kit comes with stainless-steel shafts and hardware, plus a spacer housing cast from the same alloy used in factory production. Some housings arrive painted black, while others feature an unpainted sandblasted finish—both extremely durable and corrosion-resistant.
A one-year manufacturer warranty is included.
Product Features
- Adds a true 5 inches to your Mercury outboard's shaft length
- Designed for 40–60 HP 4-Stroke Mercury outboards
- Compatible with select BigFoot & Command Thrust models
- Stainless-steel shafts and studs for long-term reliability
- OEM-grade spacer housing
- Direct bolt-on installation
- Includes all required hardware and components
- Backed by a 1-year Bay Manufacturing warranty
Compatibility Requirements
Your engine MUST match all listed specifications for proper fit.
Supported Serial Ranges
- 0T & Up — Mercury 40–60 HP 4-Stroke (4-Cylinder)
- 0G & Up — Mercury 50 HP 4-Stroke BigFoot
- 1B144686 & Up — Mercury 60 HP Command Thrust & standard 4-Stroke
- 1B020914 & Up — Additional supported 4-Stroke 4-Cylinder models
Compatible Models (From Bay Manufacturing 415 Specs)
Group 1
| HP | Stroke | Model | Serial Range |
|---|---|---|---|
| 40 | 4-Stroke | — | 0T & Up |
| 50 | 4-Stroke | 4-Cylinder | 1B020914 & Up or 0T & Up |
Group 2
| HP | Stroke | Model | Serial Range |
|---|---|---|---|
| 60 | 4-Stroke | Command Thrust / 4-Cylinder | 1B144686 & Up or 0T & Up |
Important:
- For 60 HP, this kit fits 20" → 25" conversions.
- For 60 HP converting 25" → 30", you must use the 415A Kit.
- Housing length: 17 inches
Parts Included
- (1) 5" Extension Housing
- (1) 5" Driveshaft
- (1) 5" Shift Shaft
- (1) 5" Water Tube
- (5) Studs & Nuts
- (1) Water Sleeve
- (1) Dowel Pin
- (1) Hollow Pin
Additional Information
- Produces OEM-equivalent fit and reliability.
- Increases performance in deeper water and improves handling.
- Not returnable except for verified warranty claims.
Shipping Information
Additional shipping fees to Alaska, Hawaii, U.S. Territories, or international destinations will be calculated after checkout.
A PayPal request will be emailed for any additional charges.
(Some items may be excluded from international shipping.)
Customer Support
For questions or compatibility confirmation, email: customerservice@marinepartswarehouse.com
Please include your engine model number.
