42878A2 42878C2 Mercury Exhaust Cover Plate | Genuine Used Part

🔧 Product Description

Genuine Mercury Exhaust Manifold Cover and Plate Assembly - Part Number: 42878A2

A genuine Mercury exhaust-manifold cover for selected 65HP to 90HP three-cylinder carburetted two-stroke outboards.

The service assembly is identified as 42878A2. The number 42878C2 is typically a casting or production identifier found on the physical cover and should not be treated as a separate service-kit number.

The cover works with baffle plate 428791 and gasket 43004009 to close and seal the water-cooled exhaust section of the powerhead.

⚙️ Key Features

• Genuine Mercury exhaust-manifold cover
• Correct service part number 42878A2
• Related casting reference 42878C2
• Includes or supports the internal exhaust baffle plate
• Designed for Mercury three-cylinder two-stroke powerheads

🚤 Compatibility

Commonly used on

• Mercury and Mariner three-cylinder induction and exhaust assemblies

Typically suits

• Engine models:
• Mercury 65 Jet
• Mercury 70HP three-cylinder
• Mercury 75HP three-cylinder
• Mercury 80HP three-cylinder
• Mercury 90HP three-cylinder
• Selected 75HP engines in serial range 0B240451-0C221999
• Later carburetted 65HP-90HP three-cylinder models using cover 42878A2
• HP Range: Approximately 65HP - 90HP
• Engine Type: Mercury / Mariner three-cylinder carburetted two-stroke outboard
• Year Range: Approximately late 1980s-early 2000s, dependent on serial number

🔌 Function

The cover seals the exhaust-water jacket against the cylinder block. The internal baffle directs cooling water around the exhaust passages while keeping the exhaust and cooling circuits correctly separated.

⚠️ Common Signs of Failure

• Cooling water leaks around the cover
• Exhaust staining appears at the gasket joint
• Internal corrosion damages the baffle or cover
• Cover is warped from overheating
• Mounting bolts seize or break in the cylinder block

🔄 Supersession & Cross Reference

OEM Supersession Chain

• 42878A2 → Supersedes 42878A1
• 42878A1 → Related to 42878T
• 42878A2 → Supersedes original cover 428781
• 42878C2 casting or production identifier

OEM / Related Numbers

• 42878A2
• 42878A1
• 42878T
• 428781
• 42878C2
• 428791 exhaust baffle plate
• 43004009 baffle-plate gasket
• 43004A99 related powerhead gasket set
• 82127335 cover retaining screw

Aftermarket / Verified Equivalents

• Aftermarket powerhead and exhaust-cover gasket sets replacing 43004009
• Specialist used 42878A2 / 42878T cover assemblies
• Reconditioned cover and baffle-plate assemblies
• No direct aftermarket cover casting

📦 Condition

• Genuine used part
• Supplied with the baffle plate only where fitted or stated
• Removed from running engine where applicable
• In good working condition unless otherwise stated