1965–1989 Mercury 45–115 HP 2-Stroke Outboard Motor Service & Repair Manual

This service manual covers the listed 1965–1989 Mercury 45–115 HP two-stroke outboards, including original and redesigned inline powerheads.

• Powerhead repair: Removal, disassembly, crankshaft service, connecting-rod and piston inspection, reed-block service, and reassembly for both block designs.

• Fuel and lubrication: Carburetor overhaul, fuel-pump testing, 2+2 accelerator-pump operation, Auto Blend troubleshooting, and advanced oil-injection service.

• Ignition and electrical: Distributor magneto and Thunderbolt diagnosis, stator and trigger tests, charging-circuit checks, and electric-starter repair.

• Lower unit and cooling: Cam-Shift Type I and Type II gearcase overhaul, shimming, backlash checks, and high-pressure and high-volume water-pump service.

• Power trim/tilt: System A and System B troubleshooting, bleeding, hydraulic-pump service, electric-motor repair, and cylinder overhaul.

• Controls and starting: MerControl and Commander control-box service, cable adjustments, rotary steering repair, and Type A and Type B hand rewind starters.

The overhaul and electrical-test procedures are suited to technicians and experienced outboard owners who can use pullers, precision measuring tools, and ignition test equipment.

Engine Service Coverage

Separate procedures address the original crankshaft-mounted reed arrangement and the redesigned reed housing behind the carburetors. The latter allows reed service without removing and dismantling the powerhead, an important distinction when planning a repair.

Internal work covers crankshaft bearings, connecting rods, piston and cylinder inspection, honing, check valves, and thermostat testing. Assembly cautions explain how incorrectly positioned exhaust-cover gaskets can restrict cooling flow and damage the powerhead.

Carburetors and Oil Injection

Carburetor sections distinguish the side-bowl/back-drag, integral-pump, center-square-bowl, and Series WME designs. For the 2+2 system, the text explains the different upper and lower carburetor circuits and accelerator-pump fuel routing.

Auto Blend and advanced oil injection receive separate troubleshooting sections. Coverage extends to pump removal and inspection, system purging, and low-oil warning checks. Fuel-line restriction and pump-pressure tests help separate inadequate fuel delivery from ignition faults.

Ignition Tests and Wiring Diagrams

Five ignition families are identified, from the points-type distributor magneto to Thunderbolt flywheel CD with a coil for each cylinder. Model- and serial-specific timing and synchronization sections tie the adjustments to the correct configuration.

Reference material includes Thunderbolt Stator Checks, Thunderbolt Trigger Tests, ignition-coil test drawings, and wire-identification diagrams. Charging-system diagnosis covers the stator and rectifier; cranking-motor sections include Bosch, Delco Remy, and Prestolite units.

Flywheel service identifies protector cap C-91-24161 and explains how improper puller use or hammer blows can damage crankshaft bearings.

Lower-Unit Repair and Water Pumps

Cam-Shift Type I and Type II procedures distinguish the gearcase designs, including preload-pin and Alpha driveshaft arrangements. Exploded views support bearing-carrier, propeller-shaft, driveshaft, and gear service, followed by pinion-depth and gear-backlash checks.

Separate water-pump procedures cover the high-pressure and high-volume designs. The appendix provides lower-unit oil capacities, gear ratios, backlash tables, carburetor jet/elevation charts, and piston/cylinder specifications, plus a metric conversion chart.

Trim Systems, Controls, and Seasonal Service

System A uses two trim/tilt cylinders; System B uses separate trim cylinders and a larger tilt cylinder. Their sections include electrical troubleshooting, bleeding, pump repair, and cylinder service.

MerControl and Commander coverage extends to internal control-box assemblies, neutral-start interlocks, and cable adjustments. Rotary steering, hand rewind starters, preseason checks, submerged-engine service, and winter storage are also covered. Wiring examples include power-trim circuits and a single-engine console layout.

Follow the manual's safety precautions for rotating flywheels, fuel handling, and pressurized trim systems.

A Preview of Compression and End-Play Specifications

These examples are a small sample of the manual's diagnostic and assembly specifications.

The compression-check section treats a difference of more than 15 psi between cylinders as a fault indication.

For original-design powerhead assembly, the specified crankshaft end play is 0.004–0.012 in. (0.10–0.30 mm), with a shim-adjustment procedure.

Text Search, Bookmarks, and Diagram Detail

Search and diagram detail: Embedded OCR text supports searching, though recognition errors affect some terms and numbers. Four bookmarks divide the file into large blocks rather than chapters; the first has no working destination. Small wire-color and connector-pin labels require zooming, and some ignition diagrams span facing pages.

One printable English PDF, 555 pages in total. That count includes the engine-finder page, five contents pages, and the 47-page appendix.