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Description

Center Main Crankshaft Bearing – Support Proper Crankshaft Alignment & Smooth Engine Operation

The Center Main Crankshaft Bearing is a needle bearing and retainer assembly used in the center crankshaft position of select Johnson and Evinrude outboard engines.

This bearing helps support the crankshaft between the upper and lower main bearing locations, keeping the rotating assembly properly supported and aligned as the engine operates.

On a two-stroke outboard, the crankshaft is subjected to significant combustion loads and high engine speeds. The center main bearing plays an important role in distributing those loads and allowing the crankshaft to rotate smoothly with minimal friction.

A worn, corroded, damaged, or contaminated center bearing can affect crankshaft stability and may lead to additional internal engine damage if left unaddressed.

Common Signs of a Worn or Damaged Center Crankshaft Bearing

Possible symptoms or inspection findings may include:

• Knocking, rumbling, or growling noises from the powerhead
• Increased engine vibration
• Excessive crankshaft movement or play
• Rough or inconsistent operation
• Metallic debris found inside the engine
• Pitting or corrosion on the bearing needles
• Damaged or worn bearing retainer
• Roughness when rotating the crankshaft by hand
• Heat discoloration or signs of overheating
• Accelerated wear of nearby crankshaft or bearing surfaces

These symptoms can also be caused by other internal engine components, so proper disassembly and inspection are important before determining the source of the problem.

Why the Center Main Bearing Matters

The center crankshaft bearing helps keep the crankshaft properly supported and aligned between the upper and lower bearing locations.

If this bearing develops excessive clearance or damage, the crankshaft can move beyond its intended operating position. This may place additional stress on:

• Upper and lower crankshaft bearings
• Crankshaft journals
• Connecting rods and rod bearings
• Crankshaft seals
• Center bearing liners
• Crankcase bearing surfaces
• Other internal rotating components

Maintaining proper bearing condition is especially important on engines that operate at elevated RPM or under sustained heavy load.

Key Features & Benefits

• Supports the Center of the Crankshaft – Helps maintain proper alignment and rotational stability
• Needle Bearing Design – Provides a low-friction rolling surface for crankshaft operation
• Promotes Smooth Engine Operation – Helps reduce unwanted crankshaft movement and vibration
• Protects Internal Components – Proper bearing support can help reduce wear on surrounding engine parts
• Ideal for Powerhead Rebuilds – Common replacement item during complete internal engine service
• Useful for Performance Applications – Important for engines operating at sustained or elevated RPM
• OEM Application – Part number 378252 / 0378252
• Aftermarket Cross Reference – Sierra 18-1352

Center Bearing Liner Considerations

On many OMC/Johnson/Evinrude crankshaft assemblies, bearing 378252 operates together with a split center bearing liner, commonly OEM part 310433 / 0310433.

If the center bearing shows wear, corrosion, or damage, the mating bearing liner should also be carefully inspected for:

• Scoring
• Pitting
• Uneven wear
• Excessive clearance
• Heat damage
• Surface deterioration

Replacing a damaged bearing while reusing a worn liner can shorten the life of the new bearing and may affect crankshaft alignment.

When Should Center Bearing 378252 Be Replaced?

Replacement should be considered when:

• Bearing needles show pitting or corrosion
• The bearing retainer is damaged
• The bearing feels rough or binds during inspection
• Excessive crankshaft clearance is found
• Metal contamination has circulated through the powerhead
• The engine experienced overheating or lubrication failure
• The crankshaft or crankcase has suffered internal damage
• The powerhead is being completely rebuilt and bearing condition is questionable

Bearings subjected to significant internal engine failure should be inspected very carefully, even if they do not show obvious visual damage.

Powerhead Rebuild Recommendation

When servicing the center crankshaft bearing, inspect the complete crankshaft assembly rather than treating the bearing as an isolated component.

Important inspection points include:

• Center bearing liner
• Upper crankshaft bearing
• Lower crankshaft bearing
• Crankshaft journals
• Connecting rod bearings
• Crankshaft seals
• Crankcase bearing surfaces

At Liquid Revolutions, we know that reliable crankshaft support becomes even more important in performance and race outboards where engines spend significant time at elevated RPM. Proper bearing condition helps maintain crankshaft stability, reduce internal friction, and protect the powerhead from avoidable wear.

Whether you’re rebuilding a recreational OMC/Johnson/Evinrude outboard or refreshing a performance engine, replacing a worn center crankshaft bearing can be an important part of restoring reliable and consistent engine operation.

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