27-46820 Exhaust Manifold Gasket for MerCruiser GM Big Block
27-46820 Exhaust Manifold Gasket for MerCruiser GM Big Block is backordered and will ship as soon as it is back in stock.
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27-46820 Exhaust Manifold Gasket for MerCruiser GM Big Block
27-46820 Exhaust Manifold Gasket for MerCruiser GM Big Block is backordered and will ship as soon as it is back in stock.
SERDAMARINE / MARINE EXHAUST PARTS
Exhaust Manifold Gasket — Adapter Plate to GM Manifold
This aftermarket exhaust manifold gasket (OEM reference 27-46820) seals the exhaust manifold joint on specified MerCruiser, Volvo Penta, and OMC Cobra GM-based big-block V8 marine engines (7.4L / 454 CID, 8.1L / 496 CID, and 8.2L / 502 CID). It is also used at the adapter-plate-to-GM-exhaust-manifold interface in matching two-piece Ford 460-to-GM 454 manifold conversion assemblies.
This item is a single exhaust manifold gasket component, not a complete exhaust manifold assembly or a complete manifold gasket repair kit.
27-46820 Exhaust Manifold Gasket for MerCruiser GM Big Block
Aftermarket exhaust manifold gasket referenced to MerCruiser 27-46820 for the specified GM 7.4L, 8.1L and 8.2L big-block applications. Wet-joint and dry-joint conditions remain separated below.
Engine Applications
- MerCruiser MODEL 330–370, GM V8 Big Block, 454/502 CID; Wet Joint; 1981 onward.
- MerCruiser GM V8 7.4L / 454 CID, 8.1L / 496 CID and 8.2L / 502 CID applications; match the individual exhaust assembly.
- MerCruiser GM V8 Big Block, Dry Joint; match the specific manifold gasket interface. The 6-inch configuration designation is not a gasket measurement.
- Chevrolet / Chevy 454 and 502 engine-base applications with the specified marine exhaust manifold.
Reference Numbers
The numbers below are provided as identification references across corresponding engine and aftermarket brands. They do not independently guarantee interchangeability across different manifold designs or indicate manufacturer identity; compare the complete part number (including any prefix, leading zero, and A1 suffix) along with the physical gasket shape.
| MerCruiser Reference | 27-46820, 27-46820A1, 46820, 46820A1 |
|---|---|
| Volvo Penta Reference | 3852472 |
| OMC Cobra Reference | 0508878, 0778127, 0909613, 508878, 778127, 909613, 3852472 |
| Crusader Reference | 96653 |
| Sierra Reference | 18-0418 |
| GLM Reference | 33760, 37760 |
| Mallory Reference | 9-61400 |
Supplied Parts
- Exhaust manifold gasket
Service & Installation Notes
General service guidance only. Use the service manual for your exact engine and exhaust configuration.
- Allow the engine and exhaust system to cool completely, shut off the battery switch, and prevent accidental engine cranking before starting disassembly.
- Support heavy exhaust manifold components during removal and installation to avoid damaging mounting studs, bolts, or mating surfaces.
- Clean and inspect the mating faces on the exhaust manifold and cylinder head (or adapter plate). Remove old gasket material without gouging the sealing surfaces.
- Compare the new gasket directly against the removed gasket and the sealing interface to verify port alignment and bolt hole positions. On a matching two-piece Ford 460-to-GM 454 conversion arrangement, install this gasket specifically between the adapter plate and the GM exhaust manifold.
- Tighten fasteners following the sequence and torque specifications in the engine manufacturer's service manual. After starting the engine, inspect the joint for exhaust leaks; shut down immediately and inspect if any abnormal leakage or temperature occurs.
The Serdamarine Approach
Exhaust parts need a configuration match. Serdamarine focuses on marine exhaust manifolds and their related service parts. Application details, connection requirements and public reference numbers are presented together to support part selection.
Questions Before Replacement
Can I order this gasket for any Ford 460 marine engine?
No. For Ford 460 applications, this gasket is only for the adapter-plate-to-GM-exhaust-manifold joint in a specific two-piece Ford 460-to-GM 454 manifold conversion assembly. It does not fit a standard Ford 460 cylinder-head-to-manifold joint.
Is this an exhaust elbow / riser gasket or a complete gasket kit?
Neither. Exhaust manifold gaskets and exhaust elbow/riser gaskets are separate parts serving different joints. This listing is for the individual exhaust manifold (or adapter-plate-to-GM-manifold) gasket, not a complete manifold gasket repair kit.
What are Sierra numbers 18-1957-2, 18-1982, 18-1929, 18-1933, and 18-1898?
Those are Sierra exhaust manifold part numbers associated as "use-with" assemblies for Sierra gasket 18-0418. They identify the mating exhaust manifolds rather than engine model numbers or direct gasket replacement numbers.
Related Service Parts
Sierra reference 18-0418 lists the following associated exhaust manifold assemblies for use with this gasket style (manifolds are separate components and are not included with this gasket):
- Sierra Exhaust Manifold References: 18-1957-2, 18-1982, 18-1929, 18-1933, 18-1898
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