Upper Casing Gasket – Fits Yamaha 6HP/8HP 2-Stroke (Replaces 6G1-45113-A1-00)
Upper Casing Gasket – Fits Yamaha 6HP/8HP 2-Stroke (Replaces 6G1-45113-A1-00) is backordered and will ship as soon as it is back in stock.
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Upper Casing Gasket – Fits Yamaha 6HP/8HP 2-Stroke (Replaces 6G1-45...
Product Details
This is an aftermarket Upper Casing Gasket – Fits Yamaha 6HP/8HP 2-Stroke engines, specifically designed for C, D, and J models manufactured between 1984 and 1993. It provides a reliable seal between the upper and lower casings, preventing leaks and ensuring proper engine function.
This component is a direct replacement for Yamaha part numbers 6G1-45113-00-00 and 6G1-45113-A1-00, as well as Sierra 18-99115.
- Engineered for direct replacement installation.
- Made from durable, non-metallic, paper/fiber-based gasket material.
- Effectively seals the upper casing to the lower casing.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number | Notes |
|---|---|---|
| Yamaha | 6G1-45113-A1-00 | Supersedes 6G1-45113-00-00 |
| Sierra | 18-99115 | Aftermarket Interchange |
| Mariner | 11560M | |
| Mariner | 27-11560M |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
For Yamaha models, this gasket is compatible with specific 6HP and 8HP 2-stroke engines from 1984–1993, including C, D, J, and M9 series (engine codes 6H6, 6H8, 6G1).
For Mariner outboards, this part fits certain 6HP and 8HP 2-stroke models produced between 1978 and 1986.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Yamaha | 6C (6H6) | 6 | 2-Stroke | 1984–1993 | 6G1-45113-A1-00 | Replaced 6G1-45113-00-00 |
| Yamaha | 6D (6H8) | 6 | 2-Stroke | 1984–1989 | 6G1-45113-A1-00 | Replaced 6G1-45113-00-00 |
| Yamaha | 6M9 | 6 | 2-Stroke | 1997–1998 | 6G1-45113-A1-00 | |
| Yamaha | 8N/8C (6G1) | 8 | 2-Stroke | 1984–1993 | 6G1-45113-A1-00 | Replaced 6G1-45113-00-00 |
| Yamaha | 8J (6G1) | 8 | 2-Stroke | 1986 | 6G1-45113-A1-00 | Replaced 6G1-45113-00-00 |
| Mariner | 6C | 6 | 2-Stroke | 1978–1986 | 11560M, 27-11560M | |
| Mariner | 8C | 8 | 2-Stroke | 1978–1986 | 11560M, 27-11560M |
Technical Specs
- Product Type
- Upper Casing Gasket
- Installation
- Direct replacement
- Material
- Paper/Fiber-based gasket material
- Application
- Seals upper casing to lower casing
- Dimensions (H x W x L)
- 7.0 in x 8.5 in x 0.63 in
- Other Technical Attributes
- Non-metallic gasket material
What’s in the Box
- 1 x Upper Casing Gasket (Replaces 6G1-45113-A1-00)
Installation Notes
- Ensure the engine is off and cool to the touch. Disconnect the spark plug leads and battery for safety.
- Remove the engine cowling to access internal components.
- Consult your service manual to identify and drain any necessary fluids, like engine oil or coolant.
- Carefully unbolt and remove the components obscuring the upper casing. Keep track of all hardware.
- Gently lift the upper casing away from the lower unit.
- Remove the old gasket. Use a plastic scraper to clean both mating surfaces, ensuring they are completely free of old gasket material, oil, and debris.
- Place the new gasket into position, ensuring all bolt holes align perfectly.
- Reinstall the upper casing, tightening bolts in the sequence and to the torque specifications recommended in your service manual.
- Reconnect all components, refill fluids, and reattach spark plug leads and the battery.
- Before starting the engine in water, use a flushing attachment to check for any leaks around the newly sealed area.
Troubleshooting & FAQ
How do I know if this gasket fits my engine?
This gasket is designed for specific Yamaha and Mariner 6HP & 8HP 2-stroke models listed in the compatibility table. The most reliable way to confirm fitment is to check your engine's model number and year against the table. Also, cross-reference the OEM part number (6G1-45113-A1-00). If you're unsure, visual comparison with your old part is recommended.
What are the signs of a failing upper casing gasket?
Common signs include visible oil or water leaks between the upper and lower engine casings, a loss of compression, overheating, or water contamination in the engine oil (milky appearance). Any visible damage or brittleness on the old gasket during inspection also warrants replacement.
Is any sealant required when installing this gasket?
Generally, modern fiber-based gaskets like this one are designed to be installed dry. Applying sealant can sometimes cause the gasket to slip or squeeze out, leading to a poor seal. Always follow the specific instructions in your engine's service manual, but dry installation is the standard practice.
How often should this gasket be replaced?
This gasket does not have a fixed replacement interval. It should be replaced anytime the upper casing is removed for service or repair. It should also be replaced immediately if there are any signs of a leak or damage.
What is the difference between Yamaha part numbers 6G1-45113-A1-00 and 6G1-45113-00-00?
The part number 6G1-45113-A1-00 is a supersession, meaning it is the updated, official replacement for the older 6G1-45113-00-00 part. They are functionally identical and fully interchangeable. Our aftermarket gasket is manufactured to the specifications of the latest version.
Can I reuse my old gasket?
No. Gaskets are single-use components that compress and deform to create a seal. Once compressed and exposed to heat cycles, an old gasket will not provide a reliable seal if reinstalled and is highly likely to cause leaks.
OEM vs. Aftermarket?
This listing is an aftermarket replacement (not OEM). Built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, batch-inspected for consistency.
Shipping speed & cost
We ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.
Warranty & returns
Covered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact support with your order details. Returns are accepted within our standard window (unused & in original condition). See our policy page or reach out for instructions.
Safety & Important Info
- Verify images/specifications vs your original part. If anything differs—even if your model appears compatible—do not purchase.
- This is an aftermarket replacement, not an OEM component.
- Professional installation is recommended for safety and performance.
About Sea Sierra
- Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
- Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
- Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.
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