Cylinder Block Cover Gasket for Mercury 20 HP Outboards – Replaces Mercury 27-78410, 27-52579, 27-72916
Cylinder Block Cover Gasket for Mercury 20 HP Outboards – Replaces Mercury 27-78410, 27-52579, 27-72916 is backordered and will ship as soon as it is back in stock.
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Cylinder Block Cover Gasket for Mercury 20 HP Outboards – Replaces ...
Cylinder Block Cover Gasket for Mercury 20 HP Outboards – Replaces Mercury 27-78410, 27-52579, 27-72916 is backordered and will ship as soon as it is back in stock.
Product Details
This aftermarket Cylinder Block Cover Gasket is designed for selected Mercury 20 HP outboard applications. It provides a replacement sealing interface for the cylinder block cover and is listed for Mercury 20 HP models from approximately 1978–1980.
Catalog references identify this gasket as a replacement for Mercury OEM part numbers 27-78410, 27-52579, and 27-72916. The matching aftermarket reference is Sierra 18-0372.
- Aftermarket replacement cylinder block cover gasket.
- Designed to replace the listed Mercury OEM references.
- Sold as one gasket per piece.
- Verify the engine serial number and original gasket before ordering.
Part Number Matrix
Use these verified reference numbers to compare the replacement gasket with your original part.
| Reference Type | Part Number |
|---|---|
| Mercury OEM | 27-78410 |
| Mercury OEM | 27-52579 |
| Mercury OEM | 27-72916 |
| Sierra aftermarket | 18-0372 |
Engine & Model Compatibility
The available catalog information identifies this gasket for selected Mercury 20 HP outboards, including models designated 20 and 200. A separate aftermarket catalog lists the application as 20 HP, 1978–1980.
Mercury parts catalogs show the same cylinder block cover gasket under several engine serial-number ranges. Because the stroke is not specified in the catalog records, confirm the complete model designation and serial number before installation.
| Brand | Model | Rated HP | Stroke | Application Year | Serial Number Condition | Catalog Diagram Reference |
|---|---|---|---|---|---|---|
| Mercury | 200 | 20 | Not specified | 1978–1980 application listing | 2296267 through 2827676 | Cylinder Block and Crankcase Assembly |
| Mercury | 200 | 20 | Not specified | 1978–1980 application listing | 2827677 through 3226957 | Cylinder Block and Crankcase Assembly |
| Mercury | 200 | 20 | Not specified | 1978–1980 application listing | 3226958 through 3537530 | Cylinder Block and Crankcase Assembly |
| Mercury | 200 | 20 | Not specified | 1978–1980 application listing | 4709593 and up | Cylinder Block and Crankcase Assembly |
| Mercury | 200 | 20 | Not specified | 1978–1980 application listing | 7012358 through 7098522 | Cylinder Block and Crankcase Assembly |
| Mercury | 200 | 20 | Not specified | 1978–1980 application listing | 7098523 and up | Cylinder Block and Crankcase Assembly |
| Mercury | 200 | 20 | Not specified | 1978–1980 application listing | 8006265 through 8045198 | Cylinder Block and Crankcase Assembly |
| Mercury | 200 | 20 | Not specified | 1978–1980 application listing | 8045199 and up | Cylinder Block and Crankcase Assembly |
| Mercury | 200 | 20 | Not specified | 1978–1980 application listing | 9016254 through 9157229 | Cylinder Block and Crankcase Assembly |
| Mercury | 200 | 20 | Not specified | 1978–1980 application listing | 9157230 and up | Cylinder Block and Crankcase Assembly |
Technical Specs
- Product Type
- Cylinder block cover gasket
- Product Configuration
- Single gasket; not a kit
- Application
- Selected Mercury 20 HP outboards, with a 1978–1980 application listing
- Installation
- Replacement installation at the cylinder block cover
- Mercury OEM References
- 27-78410, 27-52579, 27-72916
- Aftermarket Reference
- Sierra 18-0372
- Dimensions
- Not specified in the verified catalog information
What’s in the Box
- 1 x Cylinder block cover gasket
Installation Notes
- Ensure the engine is off and completely cool before beginning work. Follow the safety procedures in the engine service manual.
- Remove the engine cowling and any components necessary to access the cylinder block cover.
- Loosen and remove the cover fasteners evenly. Keep track of their positions if they differ.
- Carefully remove the cover without gouging or damaging the mating surfaces.
- Remove the old gasket and discard it. Do not reuse a compressed or damaged gasket.
- Clean the mating surfaces thoroughly with an appropriate scraper and solvent approved for the engine materials.
- Position the replacement gasket correctly. Do not apply sealant unless the engine service manual specifically requires it.
- Reinstall the cover and tighten the fasteners in the specified sequence and to the manufacturer’s specified torque.
- Reinstall removed components, run the engine according to the service manual, and check the cover area for leaks.
Troubleshooting & FAQ
How do I confirm that this gasket fits my engine?
Compare your engine’s brand, model, horsepower, serial number, and original gasket reference with the compatibility information above. The catalog information supports selected Mercury 20 HP applications; it does not confirm every Mercury, Johnson/Evinrude, or Chrysler model.
What is this gasket used for?
This gasket seals the cylinder block cover on the applicable Mercury outboard engine. It is listed in the engine parts diagrams as a cylinder block cover or cylinder block gasket.
Does this gasket include the cover, bolts, or sealant?
No. The package contains one replacement gasket only. The cover, fasteners, sealant, and other components are not included.
Does this listing contain an OEM gasket?
No. This listing is for an aftermarket replacement gasket. The Mercury numbers shown are OEM reference numbers used for application and interchange identification.
Does the gasket require sealant?
Sealant requirements vary by engine design and service procedure. Install the gasket according to the applicable manufacturer service manual, and do not use sealant unless it specifically calls for it.
Safety & Important Info
- Verify the complete engine model and serial number before ordering.
- Compare the replacement gasket’s shape and openings with the original gasket before installation.
- Do not rely on horsepower alone to confirm fitment.
- This is an aftermarket replacement, not a Mercury-branded OEM component.
- Professional installation is recommended when service-manual procedures or torque specifications are unavailable.
About Sea Sierra
- Marine replacement parts selected for practical fit and service applications.
- Reference-based product information to help customers compare engine models and part numbers.
- Support focused on accurate application matching before installation.
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