27-804908A00 Gasket Set Lower Unit Kit for Mercury 8HP 9.9HP 4-Stroke | JLM Marine

27-804908A00 Gasket Set Lower Unit Kit for Mercury 8HP 9.9HP 4-Stroke | JLM Marine

This Lower Unit Gasket Set is engineered to deliver a perfect fit and reliable performance for Mercury 8HP and 9.9HP 4-stroke outboard engines. Designed as a direct replacement for OEM seal kits, it ensures a seamless installation and leak-free operation for your lower unit assembly.

This kit directly replaces Mercury part numbers 27-804908A00, 27-8M0082883, 27-8M0065830, 27-804908A02, and 27-8M0060176, providing broad compatibility across multiple Mercury lower unit configurations.

• Comprehensive gasket and seal kit for complete lower unit service
• Precision-engineered to OE specifications for reliable sealing
• Fits Mercury 8/9.9 HP 4-stroke outboards (serial R042475 & up)

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket applications:

Compatible Engine Models

Confirm your engine model/year in the table below. For Mercury owners, here's a guide to help you identify your engine's serial/model: Mercury Serial Number Guide. You can also review exploded diagrams to verify part numbers: Mercury Parts Diagrams & Catalog.

Technical Specifications

Package Contents

This kit includes:

• 1× Lower Unit Seal Gasket Kit
• The package contains all the parts shown in the product picture

Installation Guide

1. Disconnect the outboard motor from the power source and allow it to cool completely.
2. Drain all gear oil from the lower unit into an appropriate container.
3. Remove the propeller, then unbolt and separate the lower unit from the mid-section housing.
4. Carefully disassemble the lower unit components, noting the position of each seal and gasket.
5. Clean all mating surfaces thoroughly, removing old gasket material and debris with a scraper and solvent.
6. Inspect all surfaces for corrosion, warping, or damage that may prevent proper sealing.
7. Install new gaskets and seals from this kit in the exact positions of the originals, ensuring correct orientation.
8. Apply a thin coat of marine-grade grease to seals to aid installation and prevent damage during assembly.
9. Reassemble the lower unit components, following your service manual's torque specifications for all fasteners.
10. Reattach the lower unit to the mid-section, ensuring proper alignment and torquing all mounting bolts to spec.
11. Refill the lower unit with the manufacturer-recommended gear oil through the fill port until it reaches the vent hole.
12. Reinstall the propeller, run the engine briefly, then recheck the gear oil level and inspect for leaks.

Troubleshooting & FAQ

Q: How do I confirm this gasket set fits my Mercury outboard?
A: Check your engine's serial number (located on the mounting bracket) and confirm it is R042475 or higher for 8HP/9.9HP 4-stroke models. Cross-reference your current part number against the five OEM numbers listed above to ensure compatibility.

Q: How often should I replace the lower unit gaskets and seals?
A: Replace gaskets and seals whenever you perform lower unit service, disassembly for propeller shaft work, or if you notice gear oil leaks or milky oil indicating water intrusion. Most manufacturers recommend lower unit service every 100 hours or annually.

Q: What are the signs that my lower unit seals have failed?
A: Common symptoms include gear oil that appears milky (water contamination), visible oil leaks around the lower unit housing, difficulty shifting gears, unusual noise from the gearcase, or rapid gear oil loss between service intervals.

Q: Can I reuse the old gaskets if they look intact?
A: No, gaskets are designed for single use only. Even if they appear undamaged, they compress during initial installation and will not seal properly when reused, leading to leaks and potential water intrusion into the lower unit.

Q: Do I need any special tools to install this gasket set?
A: You'll need basic hand tools (sockets, wrenches, screwdrivers), a torque wrench, gasket scraper, marine-grade grease, and the appropriate gear oil. A service manual for your specific engine model is highly recommended for proper torque specifications and assembly procedures.

Q: What's the difference between OEM and aftermarket gasket sets?
A: This listing is an aftermarket replacement part (not an OEM component). We build to OEM specifications using comparable-grade materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.

Q: How fast do you ship and how much does it cost?
A: We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.

Q: What is your warranty and return policy?
A: This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused & in original condition); please see our policy page or reach out for instructions.

Important Notes

• Verify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.
• This product is an aftermarket replacement part and is not an OEM component.
• Professional installation is recommended to ensure safety and optimal performance.

Why Choose JLM MARINE?

• Quality Assured: As a trusted manufacturer for over 20 years, we supply top marine brands globally.
• Fast Global Shipping: Free delivery worldwide in 5–15 days.
• Direct from Manufacturer: Competitive pricing without compromising quality.