🏷️ Basic Information Identification Make: Mercury Mercruiser Model: Marine Engines Number 6 Stern Drive Units R, MR, Alpha One, Alpha One SS Year Range: 1983-1990 Generation: First Generation (R, MR) and Second Generation (Alpha One, Alpha One SS) 📋 Manual Details Document Info Manual Type: Service Repair Workshop Manual File Format: PDF Download Language: English Compatibility: All PC based Windows operating systems and Mac Printability: All pages are printable Content Detail: Highly detailed, hundreds of photos and illustrations, step-by-step instructions ⚙️ Engine Specifications Engine Models Covered Engines: MC 120R, 140B, 185R, 488R, 898R, 228R, 260R, 120MR, 140MR, 170MR, 185MR, 190MR, 200MR, 230MR, 260MR, 300 Tempest MR, Alpha One, Alpha One SS, 3.0L Alpha One, 4.3L Alpha One, 4.3LX Alpha One, 5.7L Alpha One, 350 Magnum Alpha One, 454 Magnum Alpha One Gear Ratios Mc 120R 260R Ratios: 1.98:1 (Original) / 1.94:1 (13:21 Gears), 1.84:1 (Original) / 1.81:1 (13:21 Gears), 1.65:1 (Original) / 1.62:1 (13:21 Gears), 1.50:1 (Original) / 1.47:1 (13:21 Gears), 1.32:1 (Original) / 1.29:1 (13:21 Gears) Mc 120 Mr 300 Tempest Mr Ratios: 1.98:1 (Original) / 1.94:1 (13:28 Gears), 1.84:1 (Original) / 1.81:1 (13:28 Gears), 1.65:1 (Original) / 1.62:1 (13:28 Gears), 1.50:1 (Original) / 1.47:1 (13:28 Gears) Mc Alpha One Alpha One Ss Ratios: 1.98:1 (Original) / 1.98:1 (13:28 Gears), 1.84:1 (Original) / 1.84:1 (13:28 Gears), 1.65:1 (Original) / 1.65:1 (13:28 Gears), 1.50:1 (Original) / 1.50:1 (13:28 Gears), 1.32:1 (Original) / 1.32:1 (13:28 Gears), Alpha One SS 1.50:1 / 1.32:1 (Original) / 1.50 / 1.32:1 (13:28 Gears) Sea Ray Sterndrive Ratios: 1.98:1, 1.84:1, 1.50:1, 1.32:1 (with 13:21 gears) 🔧 Transmission Stern Drive Units Type: Stern Drive Units (R, MR, Alpha One, Alpha One SS) Gears: Various gear ratio options available, including 13:21 and 13:28, with original and service-updated ratios listed. 🔧 Maintenance Manual Sections Maintenance Coverage: Section 1B: Maintenance Troubleshooting Coverage: Section 1C: Troubleshooting Corrosion Protection: Section 7: Corrosion Protection Power Trim Coverage: Section 5: Power Trim (various pump and cylinder types) Steering Systems Coverage: Section 6: Steering Systems (Power and Manual) 📄 Service Procedures Sterndrive Unit Drive Shaft Housing Service: Section 3A: Drive Shaft Housing Gear Housing Service: Section 3B (MR/Alpha One/Alpha One SS), 3C (I-R), 3D (Alpha One Counter Rotation) Transom Assembly Transom Assembly Service: Section 4A (Minor Disassembly), 4B (Major Disassembly) 📄 Serial Number Lookup Transom Assemblies Mc Transom Assemblies Serial Range: 6216687 - 0A471374 (for R models), 0A471375 and Above (for Alpha One/Alpha One SS) Sterndrive Units Mc 120R 260R Serial Ranges: 6237861-6854392 (1.98:1), 6225577-6862701 (1.84:1), 6268065-6810537 (1.65:1), 6229158-6847029 (1.50:1), 6231571-6663947 (1.32:1) Sea Ray Sterndrives Sea Ray Serial Ranges: 0B803866-0C348031 (1.98:1), 0B800854-0C343526 (1.84:1), 0B796473-0C340666 (1.50:1), 0B804807-0C340030 (1.32:1), 0B815811-0C340333 (Transom Assembly)