Sierra 18-3904 Standard Piston Rings, OMC 394930 Cross Reference, V-4/V-6 60 Degree Eagle Series

The Sierra 18-3904 is a standard-size piston ring set engineered for OMC V-4 and V-6 60 Degree Eagle Series outboard and Sea Drive engines. Each ring is precision machined to restore proper cylinder sealing, compression, and oil control on a rebuild or overhaul, helping the engine run efficiently and preventing blow-by that leads to power loss and excess oil consumption. As a standard (STD.) size ring set, part number 18-3904 is intended for cylinders that have not been bored oversize; if a block has been bored out, a corresponding oversize ring set is required instead. Sierra manufactures these rings to correspond with the original equipment specification, and every set is backed by Sierra's standard parts warranty. This part is sold as a compact, lightweight ring set suited to marine mechanics and engine builders performing a piston ring replacement or full piston kit rebuild on qualifying OMC 60 Degree Eagle Series powerheads and Sea Drive applications.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-3904
• Product Name: Piston Rings
• Ring Size: Standard (STD.)
• Finish: Machined
• Weight: 0.08 pounds
• Product Dimensions: 0.39 x 0.39 x 0.39 inches
• UPC: 030999316981
• OEM Cross Reference: OMC 394930

Fitment

• OMC V-4 and V-6 60 Degree Eagle Series outboard engines
• OMC Sea Drive engines

Replaces (OEM)

• OMC 394930

Frequently Asked Questions

What engines does the Sierra 18-3904 piston ring set fit? The Sierra 18-3904 is designed for OMC V-4 and V-6 60 Degree Eagle Series outboard engines as well as OMC Sea Drive engines.

Is 18-3904 a standard size or oversize ring set? Part number 18-3904 is a standard (STD.) size piston ring set, meaning it is intended for cylinders at original bore diameter that have not been machined oversize.

Does the Sierra 18-3904 cross reference to an OMC part number? Yes, the Sierra 18-3904 ring set corresponds to OMC part number 394930.

How much does the 18-3904 piston ring set weigh? The 18-3904 piston ring set weighs 0.08 pounds.

What are the dimensions of the Sierra 18-3904 piston rings? Sierra 18-3904 measures 0.39 x 0.39 x 0.39 inches per the packaged listing.

What finish do the 18-3904 piston rings have? The rings in Sierra part 18-3904 have a machined finish.

When would I need an oversize ring set instead of 18-3904? If the cylinder bore on the OMC 60 Degree Eagle Series or Sea Drive block has been machined oversize during a rebuild, an oversize ring set is needed rather than the standard-size 18-3904.

Is the Sierra 18-3904 genuine Sierra manufactured or a generic aftermarket part? 18-3904 is manufactured by Sierra, a recognized marine parts brand, and is covered by Sierra's parts warranty.

What is included when I order part 18-3904? Ordering 18-3904 gets you the complete standard-size piston ring set for one piston on the applicable OMC 60 Degree Eagle Series or Sea Drive engine.

Can 18-3904 be used for a full engine rebuild? Yes, the 18-3904 standard ring set is commonly installed during a piston or engine rebuild on OMC V-4/V-6 60 Degree Eagle Series and Sea Drive engines, alongside the corresponding piston.