Improve performance and correct shaft length issues with this premium Bay Manufacturing 5" Outboard Extension Kit for Mercury 8 HP and 9.9 HP 4-stroke models. Designed for motors with a standard gearcase, this kit converts your short-shaft outboard into a long-shaft configuration—eliminating cavitation, improving handling, and restoring proper propeller depth.
Built from marine-grade materials, stainless steel shafts, and OEM-grade cast housings, this kit ensures long-lasting reliability and smooth operation.
Product Features
- Adds a true 5 inches of shaft length
- Designed for Mercury 8 HP and 9.9 HP 4-stroke outboards
- Includes all major components needed for conversion:
- 5" extension housing
- 5" drive shaft
- 5" shift shaft
- 5" water tube
- Studs, nuts, and bushing
- Stainless steel shafts and studs for long-term durability
- Spacer housing cast from OEM-grade alloy
- Available in either sandblasted unpainted finish or black-painted, depending on model batch
- Backed by a 1-Year limited warranty
Motor Compatibility Requirements
Your engine must match all listed specifications for proper fitment.
Mercury 8 HP 4-Stroke
- HP: 8
- Stroke: 4
Mercury 9.9 HP 4-Stroke
Must meet all conditions below:
- HP: 9.9
- Stroke: 4
- Model Year: 2005 and newer
- Serial Range: 0R042475 through 0R052327
Must have:
- Standard gearcase
- 6mm thread on cap bolt
- No dowel pins
Compatible Serial Groups
- 0R-series Mercury outboards
Additional Information
These extension kits are not eligible for return except for warranty claims.
Please verify your exact engine model and serial number prior to ordering.
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 to confirm compatibility, please email customerservice@marinepartswarehouse.com
Please include your engine model or serial number to help confirm proper fitment before ordering.
