Sierra 18-7111 O-Ring for OMC Sterndrive and Cobra Sterndrive Crankcase Head, 0.197 Inch ID

The Sierra 18-7111 is a rubber-based O-ring engineered for the crankcase head on OMC Sterndrive and Cobra Sterndrive engines. It seals against oil and coolant leaks at the crankcase head joint, helping maintain proper lubrication pressure and preventing contamination from water intrusion. Sized at 0.197 inch (5mm) inside diameter with a 0.113 inch (2.9mm) width, this is a small but critical sealing component that is easy to overlook during a rebuild but can cause persistent leaks or crankcase pressure loss if it is worn, hardened, or omitted.

Built from a rubber-based compound for resistance to marine fuels, oils, and coolants, the 18-7111 O-ring is sold as a single piece and is intended to be replaced any time the crankcase head is removed or serviced, rather than reused. Keeping a few of these on hand is good practice for anyone performing routine maintenance or a full rebuild on a compatible OMC or Cobra sterndrive powerhead.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-7111
• Nominal Inside Diameter: 0.197 inch (5mm)
• Width: 0.113 inch (2.9mm)
• Material: Rubber-based compound
• Weight: 0.01 pounds
• Unit Count: 1 Count
• UPC: 808282259594

Fitment

• OMC Sterndrive / Cobra Sterndrive, 4 hp, 1969-90
• OMC Sterndrive / Cobra Sterndrive, 5 thru 300 hp, 1957-90

Replaces (OEM)

• OMC 301824

Frequently Asked Questions

What does the Sierra 18-7111 O-ring fit? The Sierra 18-7111 O-ring is designed for the crankcase head on OMC Sterndrive and Cobra Sterndrive engines, covering 4 hp models from 1969-90 and 5 thru 300 hp models from 1957-90.

What size is the 18-7111 O-ring? It has a nominal inside diameter of 0.197 inch (5mm) and a width of 0.113 inch (2.9mm).

Is the Sierra 18-7111 the same as OMC 301824? Yes, the Sierra 18-7111 O-ring is the equivalent replacement for OMC part number 301824.

What material is the 18-7111 O-ring made from? It is made from a rubber-based compound designed to seal against marine oils, fuels, and coolants.

How many O-rings come in a pack? The Sierra 18-7111 is sold as a single unit, one O-ring per pack.

Where on the engine does this O-ring install? This O-ring seals the crankcase head on compatible OMC Sterndrive and Cobra Sterndrive engines.

Should the crankcase head O-ring be reused during a rebuild? No, the 18-7111 O-ring should be replaced with a new one any time the crankcase head is removed, rather than reusing the old seal.

How much does the Sierra 18-7111 O-ring weigh? It weighs 0.01 pounds.

Is the Sierra 18-7111 a genuine Sierra part or aftermarket? The 18-7111 is a Sierra-manufactured O-ring sold as a direct replacement for the OMC 301824 crankcase head seal, not a repackaged OEM part.

What symptoms indicate a failed crankcase head O-ring? Oil seepage or a loss of crankcase sealing pressure around the crankcase head is a common sign that the 18-7111 O-ring needs to be replaced.

Does the 18-7111 O-ring fit both 2-stroke and 4-stroke OMC engines? The listed fitment for the 18-7111 covers OMC Sterndrive and Cobra Sterndrive models from 4 hp (1969-90) and 5 thru 300 hp (1957-90); check your engine's hp and year against this range before ordering.

What is the UPC for the Sierra 18-7111 O-ring? The UPC for the Sierra 18-7111 crankcase head O-ring is 808282259594.