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Description

Lower Crankshaft Seal 331103 – Maintain Proper Crankcase Sealing & Engine Performance

The Lower Crankshaft Seal 0331103 is used on select Johnson, Evinrude, and OMC outboard engines to seal the lower portion of the crankshaft and help maintain proper crankcase pressure.

On a two-stroke outboard, crankcase sealing is especially important because the engine relies on changes in crankcase pressure to move the fuel air mixture through the engine. A worn, hardened, cracked, or damaged crankshaft seal can allow unwanted air into the crankcase and interfere with that process.

Even a relatively small crankshaft seal leak can lead to engine performance problems that may initially appear to be caused by the carburetors, ignition system, or fuel delivery system.

Common Signs of a Worn or Leaking Crankshaft Seal

Possible symptoms may include:

• Hard starting
• Rough or unstable idle
• Engine hesitation
• Inconsistent RPM
• Lean running condition
• Poor throttle response
• Difficulty tuning carburetors
• Engine performance that changes as the engine warms up
• Unexplained air leak symptoms
• Reduced overall engine performance

Because these symptoms can also be caused by other engine problems, proper diagnosis is important before replacing parts.

Why the Lower Crankshaft Seal Matters

A properly functioning crankshaft seal helps keep the crankcase sealed so the engine can maintain the pressure changes required for efficient two-stroke operation.

When the seal begins leaking, additional air can enter the crankcase. This can alter the air/fuel mixture and may create a lean condition that affects performance and, in severe cases, can increase the risk of engine damage.

For performance and racing applications, maintaining proper crankcase sealing is particularly important because even small air leaks can affect tuning, acceleration, and consistency throughout the RPM range.

Key Features & Benefits

• Maintains Crankcase Sealing – Helps prevent unwanted air from entering around the lower crankshaft
• Supports Proper Two-Stroke Operation – Helps maintain the crankcase pressure needed for fuel-and-air transfer
• Improves Engine Reliability – Replacing a worn seal can eliminate a potential source of air leakage
• Helps Restore Consistent Performance – Useful when diagnosing unexplained idle, tuning, or RPM issues
• Ideal for Engine Rebuilds – Common replacement item during crankshaft or powerhead service

When Should a Crankshaft Seal Be Replaced?

Replacement should be considered when:

• The seal is visibly damaged, hardened, cracked, or worn
• The engine shows signs of an unexplained crankcase air or burnt oil leak
• The crankshaft or lower bearing area is being serviced
• The powerhead is being rebuilt
• The engine has been disassembled and the existing seal has significant age or wear

Whenever a powerhead is already apart, replacing aging crankshaft seals can be inexpensive insurance compared with having to disassemble the engine again later.

Performance & Racing Considerations

At Liquid Revolutions, we know how important consistent crankcase sealing is on a performance outboard. When an engine is being pushed hard or tuned closely, even a small air leak can make diagnosing carburetion and performance issues much more difficult.

Whether you’re rebuilding a recreational Johnson/Evinrude outboard or servicing a performance or race engine, a properly installed lower crankshaft seal helps maintain predictable engine operation, reliable tuning, and consistent performance.

Always verify your engine model number, year, and original OEM part number before ordering to confirm fitment.