Closed Center-Riser Exhaust Manifold Gasket for MerCruiser GM V6/V8 – Replaces 27-8637251, 27-860231
Closed Center-Riser Exhaust Manifold Gasket for MerCruiser GM V6/V8 – Replaces 27-8637251, 27-860231 is backordered and will ship as soon as it is back in stock.
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Closed Center-Riser Exhaust Manifold Gasket for MerCruiser GM V6/V8...
Closed Center-Riser Exhaust Manifold Gasket for MerCruiser GM V6/V8 – Replaces 27-8637251, 27-860231 is backordered and will ship as soon as it is back in stock.
Product Details
This closed center-riser exhaust manifold gasket is an aftermarket replacement for selected MerCruiser stern-drive and inboard applications using General Motors V6 and V8 engines with a MerCruiser closed-cooling system. It is intended for center-exit exhaust manifolds and closed riser connections.
The company application data identifies this gasket for wet-joint configurations on GM 229/262 CID V6 engines, GM 305/350/377 CID small-block V8 engines, and GM 454/502 CID big-block V8 engines. The same gasket is also listed as a dry-joint alternative for applicable GM V6/V8 small-block installations. Confirm the joint design, cooling-system type, engine configuration, and original gasket number before ordering.
- Product type: Exhaust manifold-to-riser gasket
- Riser style: Center riser, closed or block-off design
- Cooling system: MerCruiser closed cooling / fresh-water cooling system
- Joint configurations: Wet joint; dry-joint alternative where the original application specifies it
- Quantity: One gasket
Part Number Matrix
The following manufacturer and aftermarket references are listed for identification and cross-reference purposes. They do not replace confirmation of the complete engine and exhaust configuration.
| Brand or source | Reference number |
|---|---|
| Mercury MerCruiser | 27-8637251 |
| Mercury MerCruiser | 27-863725 |
| Mercury MerCruiser | 27-860231 |
| Mercury MerCruiser | 27-41811 |
| GLM | 30220 |
| Mallory | 9-61422 |
| Sierra | 18-0672 |
| Sierra | 18-0672-9 |
| OMC | 0502988 |
| OMC | 0508715 |
Engine and Application Compatibility
Company fitment data groups this gasket by engine family and exhaust-joint design rather than by a single universal model list. Keep the engine family, horsepower range, joint type, cooling-system type, and serial-number condition together when confirming fitment.
| Engine application | Engine family | Joint configuration | Cooling system | Application notes |
|---|---|---|---|---|
| MerCruiser 175–205 | V6, GM 229/262 CID | Wet joint | Closed cooling | Center-riser exhaust manifold application; serial condition listed by the company as 1983 through 0M serial numbers. |
| MerCruiser 200–320 | V8 small-block, GM 305/350/377 CID | Wet joint | Closed cooling | Center-riser exhaust manifold application; serial condition listed by the company as 1983 through 0M serial numbers. |
| MerCruiser 330–370 | V8 big-block, GM 454/502 CID | Wet joint | Closed cooling | Center-riser exhaust manifold application; serial condition listed by the company as 1981 and up. |
| Applicable GM V6/V8 small-block applications | GM V6/V8 small-block | Dry-joint alternative | Verify system configuration | Use only where the original application specifies this gasket as the dry-joint alternative; serial condition listed by the company as 0M serial numbers and up. |
Technical Specifications
- Product type
- Exhaust manifold-to-riser gasket
- Riser design
- Center riser, closed or block-off style
- Cooling-system application
- MerCruiser closed cooling / fresh-water cooling system
- Joint application
- Wet joint; dry-joint alternative for specified GM V6/V8 small-block applications
- Replacement status
- Aftermarket replacement; not an OEM component
What’s in the Box
- 1 x Closed center-riser exhaust manifold gasket
Installation Notes
- Allow the engine to cool completely and disconnect the battery before beginning service.
- Identify the cooling-system arrangement and drain the relevant section as required by the service manual.
- Remove the riser or exhaust-manifold connection and record bolt locations and hardware condition.
- Remove the old gasket and thoroughly clean both mating surfaces. Remove gasket residue, rust, scale, and debris without damaging the sealing faces.
- Compare the new gasket with the removed gasket and verify the port pattern, bolt holes, and closed-riser design.
- Install the gasket in the correct orientation and refit the riser or manifold.
- Tighten the fasteners in the manufacturer-specified sequence and to the torque stated in the applicable service manual. Do not guess the torque value.
- Restore the cooling system, reconnect the battery, and run the engine only after all required components and fluids have been reinstalled.
- Inspect the connection for coolant, water, or exhaust leaks after startup and again after the engine reaches operating temperature.
Troubleshooting and FAQ
Is this an open or closed riser gasket?
This is a closed center-riser, block-off-style gasket. It is listed for MerCruiser closed-cooling applications. Do not substitute an open gasket unless it matches the original engine and exhaust configuration.
Does this listing include two gaskets?
No. This listing is for one gasket. A separate company record exists for a two-piece package, but that package is not the same product quantity as this single-gasket listing.
Will it fit every MerCruiser V6 or V8 engine?
No. The listed applications are limited to specified GM V6 and V8 engine families with the matching center-riser, closed-cooling configuration. Verify the original gasket number, joint style, cooling system, and engine serial condition before ordering.
What are common signs of a failed riser gasket?
Possible symptoms include coolant or water leakage at the manifold-to-riser joint, exhaust leakage, corrosion or staining around the mating surfaces, overheating, or water entering areas where it should not. Diagnose the complete exhaust and cooling system before replacing the gasket.
Should gasket sealant be used?
Use the installation method specified by the applicable engine or exhaust-manifold service manual. Do not apply sealant unless the gasket manufacturer or service procedure calls for it, because excess sealant can obstruct cooling or exhaust passages.
Is this an OEM gasket?
No. This is an aftermarket replacement gasket. The numbers shown in the part-number matrix are manufacturer, aftermarket, or cross-reference identifiers used to help verify the application.
Safety and Important Information
- Verify the original gasket number and physical port pattern before purchase.
- Confirm that your engine uses the closed-cooling system and the applicable center-riser configuration.
- Do not use an open gasket in place of a closed gasket, or a wet-joint gasket in place of a dry-joint gasket, unless the service documentation specifically confirms the substitution.
- Follow the engine manufacturer's torque sequence and service instructions.
- Professional installation is recommended when servicing exhaust manifolds, risers, or closed-cooling systems.
About Sea Sierra
- Marine replacement parts — We supply aftermarket components for common marine propulsion and exhaust-system service applications.
- Application-focused listings — Product descriptions identify cooling-system, joint-style, engine-family, and reference-number conditions where available.
- Support for fitment checks — Compare your original part number and configuration before ordering to help ensure the correct replacement.
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