27-8637251 Exhaust Elbow Block Off Gasket for MerCruiser | JLM Marine

27-8637251 Exhaust Elbow Block Off Gasket for MerCruiser

This Exhaust Elbow Block Off Gasket is designed for MerCruiser stern drive engines equipped with fresh water cooling systems. It fits a wide range of V6 and V8 engine models from the early 1980s through 2002, including popular displacements such as 4.3L, 5.0L, 5.7L, 6.2L, 7.4L (454), and 8.2L (502). The gasket is installed between the exhaust riser and manifold on center riser configurations with 3-inch or 4-inch risers.

This aftermarket replacement directly cross-references MerCruiser OEM #27-8637251, #27-860231, #8637251, #27-41811, and #27-863725, as well as Sierra parts 18-1970-2 and 18-1976-2. It is compatible with manifold part numbers including Barr MC-20-44354, Barr MC-20-98504, and various Mercury Marine manifolds (44354A series, 807914A1, 807988A series, 95755A2, 98503A2, 98504A3).

• Designed for fresh water cooled systems only—not for dry joint exhaust applications
• Two composite gaskets per package for complete riser-to-manifold sealing
• Fits center riser manifolds used from early 1980s to 2002

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 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.

Compatible Mercury Marine Manifold Part Numbers: 44354A3, 44354A9, 44354A10, 44354A13, 807914A1, 807988A2, 807988A03, 95755A2, 98503A2, 98504A3

Technical Specifications

Package Contents

Each package contains:

• 2 × Exhaust Elbow Block Off Gaskets

Installation Guide

1. Disconnect the battery and allow the engine to cool completely before beginning work.
2. Remove the exhaust riser assembly from the manifold by loosening and removing all mounting bolts.
3. Carefully scrape off old gasket material from both the riser and manifold mating surfaces using a gasket scraper. Ensure surfaces are clean and smooth.
4. Inspect the manifold and riser for cracks, corrosion, or warping; replace components if damaged.
5. Position the new composite gasket onto the manifold studs or bolt holes, aligning all openings properly.
6. Reinstall the exhaust riser onto the manifold, ensuring the gasket remains properly aligned.
7. Hand-thread all mounting bolts to prevent cross-threading, then tighten in a crisscross pattern to the manufacturer's specified torque.
8. Reconnect cooling hoses and exhaust connections, ensuring all clamps are secure.
9. Inspect for proper alignment and clearance of all components before reconnecting the battery.
10. Start the engine and check for exhaust leaks around the gasket area at idle and under load. Listen for unusual noises or hissing sounds.
11. Monitor engine temperature and exhaust system performance during the first few operating hours.
12. Re-torque bolts after initial heat cycles if recommended by your engine manual.

Troubleshooting & FAQ

How do I confirm this gasket fits my MerCruiser engine?
Verify that your engine has a fresh water cooling system with a center riser manifold (3" or 4" riser) and was built between the early 1980s and 2002. Check your manifold part number against the compatible list (Barr MC-20-44354, MC-20-98504, or Mercury Marine 44354A/807914A/807988A/98503A/98504A series). This gasket is not compatible with dry joint exhaust systems.

What are the signs that my exhaust elbow gasket needs replacement?
Common symptoms include visible exhaust leaks (steam or smoke) at the riser-to-manifold joint, hissing noises during operation, corrosion around the gasket area, or overheating due to exhaust backpressure. Inspect gaskets during routine manifold or riser service.

How often should I replace these gaskets?
Replace exhaust elbow gaskets whenever you remove the riser for service, typically during manifold or riser replacement. Many marine technicians recommend inspection every 3–5 years or whenever you notice exhaust leaks, corrosion, or during winterization/de-winterization procedures.

Why are there two gaskets in the package?
Most MerCruiser V6 and V8 engines have two exhaust risers (one per cylinder bank), so each riser-to-manifold joint requires one gasket. The package provides both gaskets needed for a complete engine service.

Can I reuse the old gasket if it looks intact?
No. Composite exhaust gaskets compress and conform to mating surfaces during initial installation and heat cycling. Reusing old gaskets can result in exhaust leaks, reduced sealing effectiveness, and potential engine damage from exhaust gas intrusion.

Is this gasket compatible with dry joint exhaust systems?
No, this gasket is designed exclusively for fresh water cooled MerCruiser engines with center riser manifolds. Do not use on dry joint exhaust configurations, as fitment and sealing requirements differ.

OEM vs. Aftermarket?
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.

How fast do you ship and how much does it cost?
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.

What is your warranty and return policy?
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.