Sierra 18-8307 Oil Seal, Lower Main Seal, Replaces OMC 331103

The Sierra 18-8307 is an Oil Seal sold as a Lower Main Seal for outboard motor applications, built to seal the lower crankcase/driveshaft area against oil loss and water intrusion. It is designed as a direct cross-reference replacement for OMC/Evinrude-Johnson part number 331103, and Sierra states that each of its parts meets or exceeds the specification of the original equipment part it replaces. The seal is precision-sized with an outside diameter of 1.628 inches, a shaft size of 1.110 inches, and a width of 0.448 inches, so it seats and rides correctly against the shaft without leaking or binding. At 0.03 pounds, it is a compact, lightweight component intended for straightforward replacement during routine maintenance or teardown of the lower unit/crankcase seal area rather than a full rebuild. The part falls under Evinrude outboard prop and driveshaft seal applications, making it relevant to technicians and boat owners servicing these outboard components. Because it is an exact-fit replacement seal rather than a universal part, matching the part number or the OMC/Evinrude-Johnson cross-reference number is the reliable way to confirm it is correct for a given engine before installation.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-8307
• Product Type: Oil Seal (Lower Main Seal)
• Outside Diameter: 1.628 inches
• Shaft Size: 1.110 inches
• Width: 0.448 inches
• Weight: 0.03 pounds
• Color: white
• UPC: 808282244934
• OEM Cross Reference: OMC 331103
• Application Category: Evinrude Outboard Prop and Driveshaft Seals

Fitment

Specific engine make, horsepower, and year fitment are not listed for this part; confirm fit by matching the OEM cross-reference number 331103 to your engine's original seal.

Replaces (OEM)

• 331103

Frequently Asked Questions

What is the Sierra 18-8307 used for? It is an Oil Seal sold as a Lower Main Seal, used to seal the lower crankcase/driveshaft area of an outboard motor against oil and water leakage.

What OEM part number does the 18-8307 replace? Sierra 18-8307 cross-references to OMC/Evinrude-Johnson part number 331103.

Is the Sierra 18-8307 a genuine or aftermarket part? It is an aftermarket Sierra part, manufactured to meet or exceed the specification of the original OMC 331103 seal it replaces.

What is the outside diameter of the 18-8307 seal? The outside diameter is 1.628 inches.

What shaft size does the 18-8307 fit? This seal is sized for a 1.110 inch shaft.

How wide is the Sierra 18-8307 seal? The width of the 18-8307 is 0.448 inches.

How much does the 18-8307 weigh? The Sierra 18-8307 weighs 0.03 pounds.

What color is the Sierra 18-8307 seal? The 18-8307 is white.

Does the 18-8307 fit a specific engine year or horsepower? No specific make, horsepower, or year range is listed for the 18-8307; fitment should be confirmed by matching the OMC/Evinrude-Johnson 331103 cross-reference number to your engine.

What category of application is the 18-8307 intended for? The 18-8307 falls under Evinrude outboard prop and driveshaft seal applications.

How is the 18-8307 different from the OEM 331103 seal? Functionally it is a direct replacement for OMC/Evinrude-Johnson 331103, dimensionally matched at 1.628 inch OD, 1.110 inch shaft size, and 0.448 inch width.

What comes in the box with the 18-8307? The Sierra 18-8307 is supplied as a single Lower Main Seal unit.