Sierra 18-0957 Adapter-to-Powerhead Gasket OMC 318373
18-0957 L3
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Sierra 18‑0957 Adapter‑to‑Powerhead Gasket
Direct Cross‑Reference to OMC 318373
Sierra replacement gasket for the adapter-to-powerhead joint on Johnson/Evinrude/OMC applications that specify OEM 318373. Manufacturer catalogue data identifies 18-0957 as an adapter-to-powerhead gasket—not a carburettor-to-silencer gasket.
Key Features
- ✔ Genuine Sierra Marine replacement gasket
- ✔ Seals the adapter-to-powerhead interface
- ✔ Direct cross-reference to OMC 318373
- ✔ Single gasket supplied
- ✔ Catalogue application number AP 1490
Technical Specs
| Brand | Sierra Marine |
| Sierra part number | 18-0957 |
| Sierra application number | AP 1490 |
| Part type | Adapter-to-powerhead gasket |
| OEM reference | 318373 |
Compatibility / Fitment Guide
| Fitment criterion | Required confirmation | Do not confuse with |
|---|---|---|
| Johnson / Evinrude / OMC outboard application | Parts diagram specifies adapter-to-powerhead gasket 318373 | Engine horsepower/year alone is not sufficiently reliable for this gasket. |
| Physical installation | Gasket is located between the powerhead and adapter assembly | Confirm shape, bolt pattern and OEM callout before disassembly. |
| Carburettor-to-silencer gasket | Not this part | OMC 333008 cross-references to Sierra 18-0975, not 18-0957. |
| Other adapter gaskets | Not interchangeable | OMC used multiple adapter-to-powerhead gaskets across V4, V6 and three-cylinder families. |
This corrected guide deliberately avoids the unsupported 'Evinrude 135 HP 1974-onward' blanket claim. The exact, defensible fitment key is OEM 318373 in the engine parts diagram.
Part Number Cross Reference
| Sierra Marine | 18-0957 |
| Sierra application number | AP 1490 |
| OMC / Johnson / Evinrude | 318373 / 0318373 |
| Not interchangeable | 333008 → Sierra 18-0975 (carb-to-silencer) |
| 4Boats SKU | 18-0957 L3 |
Cross-reference numbers identify the intended application; brand and packaging may differ.
Frequently Asked Questions
Is this a carburettor-to-silencer gasket?
No. Sierra identifies 18-0957 as an adapter-to-powerhead gasket.
Does it replace OMC 333008?
No. 333008 cross-references to Sierra 18-0975.
Which OEM number should I find?
Look for 318373 / 0318373 in the engine parts diagram.
Is it genuine Sierra?
Yes, the listing identifies the supplied part as Sierra 18-0957.
Compare the engine model code, original part number and physical installation before ordering.
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