6H4-81800-12 Aftermarket Mercury/Yamaha 40-50HP Starter Motor (1984-1988) | Sawley's Select Marine Parts

🔧 Product Description

Aftermarket Yamaha / Yamaha-Built Mariner 40-50HP Starter Motor - Part Number: 6H4-81800-12

New aftermarket Hitachi-pattern starter for early Yamaha 40HP and 50HP three-cylinder two-stroke outboards and corresponding Yamaha-built Mariner applications whose original starter carries the 6H4 reference. It is a 12-volt, 9-tooth, counter-clockwise permanent-magnet direct-drive assembly.

⚙️ Key Features

• 12-volt marine electrical system

• Counter-clockwise rotation viewed from the drive end

• 9-tooth pinion with approximately 28mm gear diameter

• Two unthreaded 8mm mounting holes

• Hitachi permanent-magnet direct-drive construction

• Correct early 6H4 starter geometry; later 40HP/50HP families use different starters

🧰 Assembly Contents

• 1 × Complete starter motor assembly - Part Number: 6H4-81800-12

• 1 × Integrated starter solenoid

• 1 × Installed 9-tooth pinion and overrunning clutch

• 1 × Installed armature, field-magnet, brushes and drive housing

• Mounting bolts and external starter wiring are not included unless specifically supplied

🔄 Supersession & Cross Reference

OEM Supersession Chain:

• 6H4-81800-12 → Supersedes 6H4-81800-11

• 6H4-81800-11 → Supersedes 6H4-81800-10

• 6H4-81800-10 → Earlier complete starter reference

OEM / Related Numbers:

• 6H4-81800-12

• 6H4-81800-12-00

• 6H4-81800-11

• 6H4-81800-10

• Hitachi S108-99A

• Hitachi S108-99B

Aftermarket / Verified Equivalents:

• Sierra Marine: 18-6422

• ARCO Marine: 3425

• API Marine: MOT5012N-AM

• Recmar: REC6H4-81800-12

• Hitachi: S108-99A / S108-99B

🚤 Compatibility

Commonly used on:

• Early Yamaha and Yamaha-built Mariner three-cylinder two-stroke starting systems

Typically suits:

• Yamaha 40EL, 40ES, 40ETL, 40L, 40S and 40SJD - 1984-1988

• Yamaha 50EL, 50ES, 50ESJD and 50ETL - 1986-1988

• Yamaha PRO50L - 1986-1988

• Mariner-branded Yamaha-built applications only where the removed starter is 6H4-81800-10, -11 or -12

• HP Range: 40-50 HP

• Engine Type: Three-cylinder carburetted two-stroke outboard

• Year Range: 1984-1988 for the verified Yamaha application groups

• Serial / Model Identification: Confirm 12V, 9 teeth, counter-clockwise rotation, the two-hole mounting nose and the original 6H4 reference. Mercury-built and later Mariner engines use different starters.

🔌 Function

The starter engages the flywheel and cranks the engine until combustion begins. Correct pinion diameter, tooth count and mounting alignment are essential to avoid flywheel damage and repeated disengagement.

Common signs of failure:

• Starter clicks but does not crank

• Slow or laboured cranking

• Grinding, clashing or pinion kick-out

• Pinion rotates without engaging the flywheel

• Intermittent operation as brushes or contacts wear

• Overheating, water ingress or burnt internal windings

📦 Condition

• Brand-new aftermarket replacement starter motor

• New and unused

• Supplied in suitable manufacturer or equivalent protective packaging