# 865657A03 12675A16 Mercruiser Flywheel Housing | Genuine Used Part

🔧 Product Description

  

Genuine MerCruiser Alpha Flywheel Housing Assembly - Part Number: 865657A03

  

A genuine used aluminium flywheel and bell-housing assembly for selected late-model MerCruiser Alpha sterndrive engines.

  

Mercury 865657A03 supersedes housing 12675A16 and earlier related housings. The assembly bolts to the rear of the engine block, encloses the flywheel and engine coupler and maintains alignment with the Alpha sterndrive input shaft. The equivalent Bravo-pattern housing is a different part and must not be substituted.

  

⚙️ Key Features

  

• Genuine MerCruiser Alpha flywheel housing

• Current Mercury reference 865657A03

• Supersedes 12675A16

• Supports rear engine mounts and driveline alignment

• Suits selected 3.0L, V6 and V8 Alpha engines

  

🔄 Supersession & Cross Reference

  

OEM Supersession Chain:

  

• 865657A03 → Supersedes 12675A16

• 12675A16 → Supersedes 12675A5 and 96120A11

• 12675A5 and 96120A11 earlier MerCruiser flywheel housings

  

OEM / Related Numbers:

  

• 865657A03

• 865657A 03

• 12675A16

• 12675A 16

• 12675A5

• 96120A11

• Alpha flywheel cover: 807260A2

• Alpha engine coupler according to engine model

• Bravo housing: 865657A04 / 12675A18 - different housing

  

Aftermarket / Verified Equivalents:

  

• No aftermarket equivalent

  

🚤 Compatibility

  

Commonly used on:

  

• MerCruiser Alpha One and Alpha One Gen II sterndrive engines

• GM-based MerCruiser petrol engines

• Late flywheel-housing and rear-main-seal assemblies

  

Typically suits:

  

• Engine models:

• MerCruiser 3.0L GM 181 inline four-cylinder

• MerCruiser 3.0L TKS Alpha

• MerCruiser 3.0L MPI Alpha

• MerCruiser 4.3L and 4.3LH V6 Alpha

• MerCruiser 4.3L carburetted Alpha

• MerCruiser 4.3L MPI Alpha

• MerCruiser 5.0L carburetted and MPI Alpha

• MerCruiser 5.7L carburetted Alpha

• MerCruiser 350 MAG MPI Alpha

• MerCruiser 350 MPI Alpha remanufactured packages

• MerCruiser 357 Alpha 4V

• Selected 377-based Alpha packages whose diagram specifies 865657A03

  

• HP Range: Engine-output dependent

• Engine Type: GM 3.0L inline four-cylinder, 4.3L V6 and 5.0L / 5.7L V8 petrol marine engine

• Year Range: Late-1990s onward, dependent on engine and serial number

  

🔌 Function

  

The housing encloses the flywheel and coupler, supports the rear engine-mount system and keeps the engine crankshaft aligned with the Alpha sterndrive input shaft.

  

Common signs of failure:

  

• Cracks around rear mounting bosses

• Corroded or stripped bolt holes

• Engine-to-drive alignment cannot be achieved

• Couplers repeatedly fail

• Flywheel or coupler contacts the housing

• Abnormal rear-engine vibration

• Water or debris enters the flywheel area

• Housing is distorted following impact or incorrect lifting

  

📦 Condition

  

• Genuine used part

• Removed from running engine where applicable

• In good working condition unless otherwise stated

## Details

- **Price:** 200.0 AUD
- **Vendor:** Sawley's Auto and Marine
- **Tags:** Sawley’s AAM Used Parts – Flywheels | Engine Flywheels & Ring Gears

## Variants

| Variant | Price | Available |
|---------|-------|-----------|
| Default Title | 200.00 AUD | In stock |

## Images

- 865657A03 12675A16 Mercruiser Flywheel Housing | Genuine Used Part
- 865657A03 12675A16 Mercruiser Flywheel Housing | Genuine Used Part

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> Source: [Sawley's Auto and Marine](https://www.sawleysautoandmarine.com.au/products/865657a03-12675a16-mercruiser-flywheel-housing-genuine-used-part)
> Updated: 2026-07-12