20120778A Mercruiser Flywheel Housing Cover | Genuine Used Part

🔧 Product Description

Genuine VM Motori / MerCruiser 4.2L Inboard Flywheel Housing Cover - Part Number: 20120778A

A genuine used VM Motori flywheel housing cover for selected MerCruiser and Cummins MerCruiser 4.2-litre inline six-cylinder diesel inboard engines.

VM Motori reference 20120778A replaces Mercury MerCruiser housing references 881787 and 815928 and is used on MD706 LB, LX, MS and MX marine engines.

⚙️ Key Features

• Genuine VM Motori / MerCruiser flywheel housing cover
• Correct VM reference 20120778A
• Replaces Mercury 881787 and 815928
• Designed for selected 4.2L MD706 inboard engines
• Supports the rear engine and transmission interface

🚤 Compatibility

Commonly used on

• VM Motori MD706 marine diesel engines
• MerCruiser and Cummins MerCruiser 4.2L inline-six inboard packages
• Inboard flywheel-housing and transmission-adaptor assemblies

Typically suits

• Engine models:
• VM Motori MD706 LB
• VM Motori MD706 LX
• VM Motori MD706 MS
• VM Motori MD706 MX
• MerCruiser 4.2L inline-six VM diesel inboard applications
• Cummins MerCruiser 4.2L Unification inboard applications using 881787 or 815928
• ZF-transmission installations whose flywheel-housing diagram specifies these numbers
• HP Range: Approximately 230HP - 320HP across the listed MD706 variants
• Engine Type: 4.164L inline six-cylinder, direct-injection, turbocharged and intercooled marine diesel
• Year Range: Engine-model and housing-number controlled

🔌 Function

The flywheel housing cover encloses and supports the rear flywheel area while providing the structural interface between the engine block and the inboard transmission or adaptor assembly.

⚠️ Common Signs of Failure

• Cracks around mounting bosses or bolt holes
• Transmission or rear-engine alignment problems
• Oil or contamination entering the flywheel area
• Damaged transmission mounting face
• Corroded or stripped mounting threads
• Abnormal vibration from the rear of the engine
• Cover distorted after impact or incorrect installation
• Repeated coupling or drive-plate wear caused by misalignment

🔄 Supersession & Cross Reference

OEM Supersession Chain

• 20120778A VM Motori replacement flywheel-housing cover
• 881787 → Supersedes 815928
• 815928 earlier Mercury MerCruiser housing reference

OEM / Related Numbers

• VM Motori: 20120778A
• VM Motori: 20120778
• Mercury MerCruiser: 881787
• Mercury MerCruiser: 815928
• Related MerCruiser cover-plate application: 4.2L L6 VM
• Related inboard transmission arrangement: ZF transmission configuration

Aftermarket / Verified Equivalents

• No aftermarket equivalent

📦 Condition

• Genuine used part
• Removed from running engine where applicable
• In good working condition unless otherwise stated