Sierra 18-3910 Piston Ring, Replaces OMC 396377, for Johnson/Evinrude 25-35 HP 2-Cyl and 60-75 HP 3-Cyl Outboards, 3.000 Inch Standard Bore

The Sierra 18-3910 is a piston ring built for Johnson and Evinrude outboard motors, sized for a 3.000 inch standard bore. It is designed to replace OEM part number 396377 and is machined to match or exceed the fit, seal, and performance of the original equipment ring it replaces. This ring is used in two distinct outboard applications: 25-35 HP models with a 2-cylinder configuration, and 60-75 HP models with a 3-cylinder configuration, both sharing the same 3.000 inch standard bore size and the same 396377 OEM cross-reference. Because piston rings maintain the compression seal between the piston and cylinder wall, using a correctly sized, precision-machined ring is important for restoring proper compression and preventing blow-by after a rebuild or when replacing worn rings. The 18-3910 is sold to be installed as part of a piston ring set during an engine rebuild or top-end service on the applicable Johnson/Evinrude powerheads. Confirm your engine's horsepower rating, cylinder count, and bore size against the fitment details below before ordering, since piston rings are precision-fit components and the wrong bore size will not seal correctly.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-3910
• UPC: 030999542755
• Category: Evinrude Outboard Inline Piston & Rings
• Bore Size: 3.000 inches, standard
• Cylinder Configuration: 2-cylinder and 3-cylinder applications
• OEM Cross Reference: 396377
• Fitment - Horsepower: 25-35 HP (2-cylinder), 60-75 HP (3-cylinder)
• Finish: Machined
• Weight: 0.07 pounds
• Product Dimensions: 0.39 x 0.39 x 0.39 inches

Fitment

• Johnson/Evinrude 25-35 HP, 2-cylinder, 3.000 inch standard bore
• Johnson/Evinrude 60-75 HP, 3-cylinder, 3.000 inch standard bore

Replaces (OEM)

• 396377

Frequently Asked Questions

What outboard motors does the Sierra 18-3910 piston ring fit? The Sierra 18-3910 fits Johnson/Evinrude outboards in two configurations: 25-35 HP models with a 2-cylinder engine, and 60-75 HP models with a 3-cylinder engine. Both share a 3.000 inch standard bore size.

What OEM part number does the 18-3910 replace? It replaces OEM part number 396377. The Sierra 18-3910 is machined to match the fit and performance of that original equipment piston ring.

What bore size is the Sierra 18-3910 ring designed for? This ring is sized for a 3.000 inch standard bore, not an oversized bore, so it is intended for cylinders that have not been bored out.

Is the 18-3910 a single ring or a full ring set? The Sierra 18-3910 is listed and sold as a piston ring for the applicable Johnson/Evinrude cylinder; confirm quantity needed per piston when ordering for a full rebuild.

How much does the 18-3910 piston ring weigh? The Sierra 18-3910 weighs 0.07 pounds.

What are the dimensions of the Sierra 18-3910? The Sierra 18-3910 measures approximately 0.39 x 0.39 x 0.39 inches.

Will the 18-3910 work on both 2-cylinder and 3-cylinder Johnson/Evinrude engines? Yes. The same Sierra 18-3910 part number is used for the 25-35 HP 2-cylinder application and the 60-75 HP 3-cylinder application, since both use a 3.000 inch standard bore.

Is the Sierra 18-3910 a genuine OEM part or an aftermarket replacement? The 18-3910 is a Sierra-branded replacement part manufactured to replace OEM number 396377, not an original Johnson/Evinrude branded part.

What finish does the 18-3910 piston ring have? The Sierra 18-3910 has a machined finish.

How do I know if I need the standard bore ring or an oversized ring? The 18-3910 is the standard 3.000 inch bore version; if your cylinder has been bored oversize, you need a different part number sized for that oversize bore rather than the 18-3910.

What horsepower range covers the 18-3910 on a 2-cylinder engine versus a 3-cylinder engine? On a 2-cylinder engine the 18-3910 covers the 25-35 HP range, while on a 3-cylinder engine it covers the 60-75 HP range.