# 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

  

🔄 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

  

🚤 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

  

📦 Condition

  

• Genuine used part

• Removed from running engine where applicable

• In good working condition unless otherwise stated

## Details

- **Price:** 225.0 AUD
- **Vendor:** Sawley's Auto and Marine
- **Tags:** Sawley’s AAM Used Parts – Flywheels | Engine Flywheels & Ring Gears

## Variants

| Variant | Price | Available |
|---------|-------|-----------|
| Default Title | 225.00 AUD | In stock |

## Images

- 20120778A Mercruiser Flywheel Housing Cover | Genuine Used Part
- 20120778A Mercruiser Flywheel Housing Cover | Genuine Used Part
- 20120778A Mercruiser Flywheel Housing Cover | Genuine Used Part
- 20120778A Mercruiser Flywheel Housing Cover | Genuine Used Part
- 20120778A Mercruiser Flywheel Housing Cover | Genuine Used Part
- 20120778A Mercruiser Flywheel Housing Cover | Genuine Used Part
- 20120778A Mercruiser Flywheel Housing Cover | Genuine Used Part
- 20120778A Mercruiser Flywheel Housing Cover | Genuine Used Part

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> Source: [Sawley's Auto and Marine](https://www.sawleysautoandmarine.com.au/products/20120778a-mercruiser-flywheel-housing-cover-genuine-used-part)
> Updated: 2026-07-12