Sierra Powerhead Gasket Set 18-4303-1, Replaces 389556 391300 439085, Johnson/Evinrude Outboard

The Sierra Powerhead Gasket Set, part number 18-4303-1, is a complete gasket kit for Johnson/Evinrude (OMC/BRP) outboard powerheads. It is designed to restore proper sealing across the powerhead during a rebuild or gasket replacement, helping prevent oil, fuel, and coolant leaks at the mating surfaces it covers. The set includes multiple individually numbered gaskets packaged together as a single kit, including a fuel pump mounting gasket (Sierra 18-0850, equivalent to OEM 303615) and a by-pass cover gasket (Sierra 18-2876), along with the other gaskets needed for the application.

This set replaces OEM numbers 389556, 391300, and 439085, so it can be ordered using any of those original part numbers as a reference. It ships as one complete set with a package quantity of 1, making it a straightforward one-part solution for a powerhead gasket job rather than sourcing individual gaskets separately. The set is intended for Johnson/Evinrude (OMC/BRP) outboard engines.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-4303-1
• Product Name: Powerhead Gasket Set
• Application: Outboard - Johnson/Evinrude (OMC/BRP)
• Package Quantity: 1
• Weight: 0.91 pounds
• UPC: 808282259167
• Contents: Fuel Pump Mounting Gasket (18-0850, O.E. 303615, Qty 1), By-Pass Cover Gasket (18-2876), plus additional powerhead gaskets included in the set
• OEM Cross Reference: 389556, 391300, 439085

Fitment

• Johnson/Evinrude (OMC/BRP) outboard engines

Replaces (OEM)

• 389556
• 391300
• 439085

Frequently Asked Questions

What is included in the Sierra 18-4303-1 Powerhead Gasket Set? The set includes a fuel pump mounting gasket (Sierra 18-0850, equivalent to OEM 303615) and a by-pass cover gasket (Sierra 18-2876), along with the other gaskets needed for a Johnson/Evinrude outboard powerhead job, all packaged together as one kit with a package quantity of 1.

Which OEM part numbers does 18-4303-1 replace? Sierra 18-4303-1 replaces OEM numbers 389556, 391300, and 439085, so any of those numbers can be used to confirm this is the correct set.

What engines is the 18-4303-1 Powerhead Gasket Set designed for? This gasket set is designed for Johnson/Evinrude (OMC/BRP) outboard engines that use the powerhead gaskets covered under Sierra part number 18-4303-1.

How much does the Sierra 18-4303-1 gasket set weigh? The complete set weighs 0.91 pounds.

Is this a complete powerhead gasket kit or a single gasket? It is a complete set containing multiple gaskets, including the fuel pump mounting gasket and by-pass cover gasket, rather than a single individual gasket.

Can I order this set using OEM number 391300 or 389556 instead of the Sierra number? Yes, part number 18-4303-1 is the direct equivalent to OEM numbers 391300, 389556, and 439085, so ordering by any of those numbers will get you this same set.

Is the Sierra 18-4303-1 gasket set genuine Sierra manufacturing or a generic aftermarket copy? It is manufactured by Sierra under part number 18-4303-1 as a direct-fit aftermarket replacement for the listed OEM numbers.

What is the package quantity for this gasket set? The Sierra 18-4303-1 Powerhead Gasket Set ships with a package quantity of 1 complete set.

Does the 18-4303-1 set include the by-pass cover gasket? Yes, the by-pass cover gasket, Sierra part 18-2876, is included as part of the 18-4303-1 Powerhead Gasket Set.

What is the fuel pump mounting gasket's OEM equivalent in this set? The fuel pump mounting gasket included in this set is Sierra 18-0850, which corresponds to OEM number 303615.