Sierra Piston Ring Set 18-3911,.020 Oversize 3.020 Inch Bore, Fits 25-35 HP 2-Cyl and 60-75 HP 3-Cyl Outboards, Replaces 396378

The Sierra 18-3911 is a piston ring set engineered for outboard engines with a.020 inch overbore, giving the piston a 3.020 inch bore diameter once the cylinder has been rebored.020 inch over standard. It is designed for use on 25-35 HP 2-cylinder outboards and on 60-75 HP 3-cylinder outboards that share the same 3.020 inch bore specification, making it a common rebuild part for these Evinrude inline engine families. The set directly replaces OEM piston ring number 396378, so it can be installed as a like-for-like match during a piston and ring rebuild without altering the original engine specification.

Piston rings seal the combustion chamber, control oil consumption, and transfer heat away from the piston to the cylinder wall, so fitting the correct oversize is critical to maintaining proper compression and preventing blow-by after a cylinder has been bored. Because 18-3911 is sized specifically for the.020 inch overbore, it should only be installed after the block has been machined to that dimension; a standard-bore engine requires the standard-size ring set instead. This part is sold under Sierra's own part numbering and is built to the compact dimensions and light weight typical of a small-engine ring set, making it easy to stock alongside the matching piston, wrist pin, and circlip parts used in the same rebuild.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-3911
• Product Type: Piston Ring Set
• UPC: 030999542762
• Weight: 0.06 pounds
• Product Dimensions: 0.39 x 0.39 x 0.39 inches
• Cylinder Bore Size: 3.020 inches (.020 inch oversize)
• Application: 25-35 HP 2-cylinder outboard; 60-75 HP 3-cylinder outboard
• OEM Cross Reference: 396378
• Category: Evinrude Outboard Inline Piston and Rings

Fitment

• 25-35 HP, 2-cylinder outboard, 3.020 inch bore (.020 inch oversize)
• 60-75 HP, 3-cylinder outboard, 3.020 inch bore (.020 inch oversize)

Replaces (OEM)

• 396378

Frequently Asked Questions

What OEM number does the Sierra 18-3911 piston ring set replace? It replaces OEM piston ring number 396378, so the Sierra 18-3911 is a direct cross-reference for engines calling for that OEM part.

What engines does part number 18-3911 fit? This piston ring set fits 25-35 HP 2-cylinder outboards and 60-75 HP 3-cylinder outboards that use a 3.020 inch cylinder bore.

Is the 18-3911 ring set a standard bore size or an oversize? It is a.020 inch oversize set, sized for a 3.020 inch bore after the cylinder has been rebored.020 inch over standard.

Can I install 18-3911 in a standard-bore engine that has not been rebored? No. The 18-3911 piston ring set is machined for a 3.020 inch bore (.020 inch oversize) and is not intended for a standard-bore cylinder.

How much does the Sierra 18-3911 piston ring set weigh? The 18-3911 piston ring set weighs 0.06 pounds.

What are the physical dimensions of the 18-3911 piston ring set? Sierra part 18-3911 measures 0.39 x 0.39 x 0.39 inches.

What wrist pin is used with the same.020 oversize engines as 18-3911? Engines using the 18-3911.020 oversize piston ring set use wrist pin OEM part number 320954.

What circlip is paired with the 18-3911 piston ring set application? The matching circlip for these.020 oversize applications is Sierra part 18-4290, which corresponds to OEM number 317831.

Who manufactures part number 18-3911? Part number 18-3911 is manufactured by Sierra.

Is there a standard-bore or.030 oversize version of this piston ring for the same engines? Yes. The same 25-35 HP and 60-75 HP engine applications also use a standard-bore ring set (OEM 396377) and a.030 inch oversize ring set (OEM 396379), which are different Sierra part numbers than the.020 oversize 18-3911.

What is the UPC for the Sierra 18-3911 piston ring set? The UPC for Sierra 18-3911 is 030999542762.