Sierra Rear Main Seal 18-0612 - Replaces Mercruiser 809910, 14259 - GM Small Block V8

The Sierra 18-0612 is a one-piece rear main seal engineered for GM Small Block V8 engines built with a right-handed dipstick, as used in Mercruiser sterndrive applications. This seal fits between the engine block and the crankshaft flange at the rear of the engine, sealing the crankshaft bore to keep engine oil from leaking past the crankcase. Sierra manufactures the 18-0612 to OEM interchange standards so it installs as a direct equivalent without requiring modification, cross-referencing to Mercruiser OEM numbers 809910 and 14259.

The 18-0612 is one of several rear main seals in Sierra's lineup, each matched to a specific engine family and dipstick orientation. Because the correct seal depends on whether the block is GM Small Block, Big Block, or V6, and whether the dipstick is left- or right-handed, ordering the exact part number for your engine is important to get a proper seal. The 18-0612 is specifically the one-piece design for GM Small Block V8 engines with a right-handed dipstick.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-0612
• Product Type: Rear Main Seal
• Seal Type: 1-Piece
• Engine Compatibility: GM Small Block V8 (Right Handed Dipstick)
• OEM Cross Reference: 809910, 14259
• Weight: 7.48 pounds

Fitment

• Mercruiser sterndrive engines: GM Small Block V8 (Right Handed Dipstick)

Replaces (OEM)

• 809910
• 14259

Frequently Asked Questions

What does the Sierra 18-0612 rear main seal fit? The 18-0612 is a one-piece rear main seal built for GM Small Block V8 engines with a right-handed dipstick, as used in Mercruiser sterndrive applications.

Is the 18-0612 a one-piece or two-piece seal? One piece. The 18-0612 uses a single-piece rear main seal design, while Sierra's 18-0613 is the two-piece version built for the same GM Small Block V8 engine.

Which OEM numbers does the 18-0612 replace? It replaces Mercruiser OEM numbers 809910 and 14259.

Will the 18-0612 fit a GM Big Block V8? No. Big block V8 applications use Sierra 18-0614 (one-piece) or 18-0615 (two-piece); the 18-0612 is built specifically for GM Small Block V8 engines.

Why does the dipstick side matter for this seal? GM Small Block V8 engines are produced in both left- and right-handed dipstick configurations, and the 18-0612 is engineered for the right-handed dipstick version, so it must be matched to that configuration to seal properly.

How much does the 18-0612 weigh? The Sierra 18-0612 rear main seal weighs 7.48 pounds.

Is this a genuine Sierra part or an aftermarket copy? The 18-0612 is manufactured by Sierra to OEM specifications as a direct replacement for Mercruiser 809910 and 14259.

What is included when I order the 18-0612? Each order of the 18-0612 includes one rear main seal unit.

Does the 18-0612 work on a GM V6 engine? No. GM V6 engines use the separate Sierra 18-0616 rear main seal; the 18-0612 is designed only for GM Small Block V8 engines.

What Mercruiser engines use the 18-0612 seal? Mercruiser GM Small Block V8 engines with a right-handed dipstick use the 18-0612, which cross-references to OEM 809910 and 14259.

How is the 18-0612 different from the 18-0614? The 18-0612 is the one-piece rear main seal for GM Small Block V8 engines, while the 18-0614 is the corresponding one-piece seal for GM Big Block V8 engines; the two are not interchangeable.

Is the 18-0612 sold as a single seal? Yes, the Sierra 18-0612 rear main seal ships as a single unit weighing 7.48 pounds.