689-11181-00 Cylinder Head Gasket for Yamaha Mercury Mariner C30 30A W30 | JLM Marine

Cylinder Head Gasket – Fits Yamaha & Mercury Mariner 2-Stroke 25–30 HP Outboards

This aftermarket cylinder head gasket is engineered for Yamaha and Mercury Mariner 2-stroke outboard engines rated at 25–30 HP. It is designed to fit models including Yamaha C30 and 30A, as well as Mercury Mariner 30A and W30 with 2-cylinder, single-carburetor configurations. Built to OEM specifications, this gasket ensures a reliable seal between the cylinder head and block, preventing combustion leaks and maintaining optimal engine performance.

This gasket directly replaces multiple OEM part numbers across Yamaha and Mercury Mariner systems, including Yamaha 689-11181-00 and Mercury 27-19138M. It offers broad compatibility with legacy part numbers, ensuring you can confidently service older or discontinued engine models without sourcing hard-to-find original components.

• Direct replacement for Yamaha 689-11181-00 and Mercury 27-19138M part numbers
• Designed for 2-stroke, 2-cylinder engines with single carburetor
• Ensures proper compression and prevents coolant/oil mixing

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands.

Compatible Engine Models

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

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

• 1 × Outboard Cylinder Head Gasket

Installation Guide

1. Disconnect the battery and allow the engine to cool completely before beginning work.
2. Remove the engine cowling and label all electrical connections for easy reassembly.
3. Detach fuel lines and control cables from the cylinder head area. Cap open fuel lines to prevent spills.
4. Unbolt and lift off the cylinder head carefully, noting the positions of all fasteners.
5. Remove the old gasket and thoroughly clean both the cylinder head and block mating surfaces. Use a gasket scraper and solvent; ensure no residue or debris remains.
6. Inspect the cylinder head for warping or cracks using a straight edge. Replace or resurface if necessary.
7. Position the new gasket on the block, aligning all bolt holes and coolant passages precisely.
8. Reinstall the cylinder head and hand-tighten all bolts to ensure proper seating.
9. Torque the head bolts in a cross-pattern sequence to manufacturer specifications (consult your service manual).
10. Reconnect fuel lines, control cables, and electrical connections in reverse order of removal.
11. Refill coolant (if applicable) and check for leaks before starting the engine.
12. Start the engine and inspect for proper compression, coolant leaks, and smooth operation. Re-torque head bolts after initial run-in if recommended.

Troubleshooting & FAQ

Q: How do I confirm this gasket fits my engine?
A: Cross-reference your engine's model number and serial number with the compatibility table above. Verify that your engine is a 2-stroke, 2-cylinder configuration with a single carburetor and matches the listed HP range (25–30 HP).

Q: What are the signs that my cylinder head gasket needs replacement?
A: Common symptoms include loss of compression, overheating, white smoke from the exhaust, coolant mixing with oil, external coolant or oil leaks near the head, and rough idling or misfires.

Q: Can I reuse the old gasket if it looks intact?
A: No. Cylinder head gaskets are designed for single use. Reusing an old gasket—even if it appears undamaged—can result in improper sealing, leaks, and engine damage.

Q: Do I need to resurface the cylinder head before installing this gasket?
A: Inspect the cylinder head with a straight edge. If warping or damage is present, resurfacing is required. Clean, flat mating surfaces are essential for a proper seal.

Q: How often should I replace the cylinder head gasket?
A: Replace the gasket any time the cylinder head is removed for service, repair, or inspection. Regular replacement intervals are not specified, but symptoms of failure (overheating, leaks, compression loss) indicate immediate replacement is needed.

Q: Is this an OEM or aftermarket part?
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.