1547-5523a18 Mercruiser Pre-Alpha Upper Unit | Genuine Used Part

🔧 Product Description

Genuine MerCruiser Pre-Alpha Upper Gearcase Housing - Part Number: 1547-5523A18

A genuine used MerCruiser upper-drive housing for selected early Pre-Alpha stern-drive assemblies.

The housing forms the structural upper gearcase that supports the vertical drive shaft, input gear set, bearing assemblies, universal-joint connection and upper drive cap.

This listing should be matched by casting number, gearcase design, input-shaft arrangement and drive ratio before installation.

⚙️ Key Features

• Genuine used MerCruiser Pre-Alpha upper housing
• Correct assembly / casting reference 1547-5523A18
• Early stern-drive upper gearcase configuration
• Suitable for rebuilding an original Pre-Alpha drive
• Housing-only or assembled condition as shown in the product listing

🚤 Compatibility

Commonly used on

• Early MerCruiser Pre-Alpha stern drives
• Upper-drive assemblies fitted before the Alpha One designation
• Four-cylinder and selected early six-cylinder drive packages depending on ratio and gear set

Typically suits

• Drive families:
• MerCruiser MC-I / Pre-Alpha drives
• Early MerCruiser No. 1 stern drives using housing 5523A18
• Selected 120HP and 140HP four-cylinder packages
• Selected early inline-six and V6 packages when fitted with the correct gears, bearings and input shaft
• Applications requiring direct casting-number confirmation
• Engine Type: MerCruiser petrol sterndrive
• Drive Type: Pre-Alpha / early MerCruiser No. 1 upper gearcase
• Year Range: Approximately 1960s through early 1980s
• Fitment Control: Casting number, drive serial number and gear ratio must match

🔌 Function

The upper housing supports the input and vertical drive gears that transfer engine power through the universal-joint shaft into the lower drive unit.

⚠️ Common Signs of Failure

• Bearing bores are worn or damaged
• Housing is cracked after impact or gear failure
• Gear lubricant leaks from damaged sealing surfaces
• Corrosion develops around the water passage or bearing carrier
• Upper gears are noisy or have excessive backlash
• Input or vertical shaft bearings fail
• Mounting or cap threads are stripped
• Housing has internal damage from broken gears

🔄 Supersession & Cross Reference

OEM Supersession Chain

• 1547-5523A18 original Pre-Alpha upper-gearcase housing reference

OEM / Related Numbers

• 1547-5523A18
• 5523A18
• 1547-5523
• Related early MerCruiser Pre-Alpha upper-unit housing family
• 1547-9412A18 related later Alpha / MR-style upper housing
• 1547-3546A9 related four-cylinder Pre-Alpha upper-unit assembly

Aftermarket / Verified Equivalents

• Aftermarket complete Pre-Alpha replacement upper units are application and ratio dependent
• Aftermarket bearings, seals, gears and universal-joint components are available separately
• No direct aftermarket equivalent verified for the bare 5523A18 housing

📦 Condition

• Genuine used part
• Verify whether the listing includes internal gears and components or the empty housing only
• Removed from running drive where applicable
• In good working condition unless otherwise stated