1964–1986 OMC Sterndrive Service Manual for In-Line 4/6-Cylinder, GMC V6/V8 & Ford V8 Engines (P/N 1051858)

This OMC Sterndrive service manual covers the 1964–1986 range, with engine service sections for GMC in-line four- and six-cylinder engines, GMC V6 and V8 engines, and Ford V8 engines. It brings engine repair, stern-drive overhaul, electrical diagnosis, and control-system adjustments together in one reference.

PDF Search, Chapter Bookmarks, and Diagram Detail

Search and diagram access: OCR text search is available throughout the main chapters and appendix, although recognition errors can affect individual search results. Embedded bookmarks open the chapters, appendix, and wiring section. Small wiring labels require zooming, and some fine diagram lines are faint.

The download contains one printable English-language PDF with 574 pages, including one cover page, five contents pages, and one blank final page. The specification tables and wiring diagrams are included in that total.

Engine, Stern-Drive, and Control-System Service

These selected service topics sit alongside guidance on propeller selection and off-season storage.

• Engine repair: Engine removal and installation, cylinder-head reconditioning, piston and connecting-rod service, camshaft inspection, crankshaft work, and timing-chain installation.

• Fuel systems: Fuel-pump testing and carburetor overhaul, with bench adjustments for Rochester BC, 2GC, and 4MV units, Carter RBS carburetors, and Holley designs.

• Ignition service: Primary- and secondary-circuit tests, spark-plug troubleshooting, and distributor service for Delco-Remy, Mallory, Autolite, and Prestolite systems.

• Electrical diagnosis: Charging-system troubleshooting, separate and integral voltage regulators, starter testing, and overhaul procedures for Delco-Remy, Autolite, and Prestolite starters.

• Controls and steering: Shift-box repair, throttle-cable installation, SelecTrim service, hydraulic pump and motor checks, and Tru-Course and mechanical steering adjustments.

• Stern-drive overhaul: Upper and lower gearcase disassembly, ball-gear service, bearing shimming, shift-converter adjustment, power-assist servo repair, and intermediate-housing service.

The overhaul sections are suited to mechanics and experienced owners who can use precision measuring equipment and the specified pullers, presses, and shimming tools.

Engine Inspection, Fuel Delivery, and Cooling

The engine chapter separates mechanical troubleshooting from the repair procedures for each engine family. Compression, leak, and vacuum tests support diagnosis before teardown; the repair sections then cover cylinder bores, valve guides and seats, hydraulic lifters, bearing fits, and timing components.

Step-by-step instructions cover major work such as piston-and-rod disassembly, camshaft removal and installation, and cylinder-head assembly. Inspection limits and component-specific torque tables accompany the procedures.

Fuel-system coverage distinguishes single- and dual-diaphragm pumps and includes pressure and delivery tests. Carburetor sections explain the individual circuits before covering disassembly, inspection, reassembly, and adjustments. The dual-diaphragm pump is treated as a replacement assembly when defective.

Cooling coverage includes exhaust manifolds and elbows, thermostat replacement, circulation tests, and water-pump service. The manual repeatedly warns that running without water circulation can damage the lower-unit water pump.

Drive Variants, Shift Adjustment, and Bearing Setup

The stern-drive chapter distinguishes Electromatic shifting from mechanically assisted power shifting and later mechanical linkage. Separate procedures address the early lower-unit designs and the later propeller-exhaust units, so the drive design matters when selecting the repair section.

The manual breaks down intermediate-housing boot service, ball-gear driveshaft work, shift-cable replacement, and lower-unit rebuilding. Its variant-specific instructions help match the adjustment and shimming procedure to the assembly being serviced.

Special-tool references include shimming tools 908573 for the 400 and 800 stern drives and 908572 for the specified 3.8-liter application. The bearing sections explain how an unbroken oil film can distort shim measurements and produce an incorrect bearing setup.

Tilt Diagnosis, Steering, and Electrical References

Tilt troubleshooting separates electrical faults from mechanical problems involving the hammer-blow coupling, clutch pack, and worm gear. SelecTrim coverage includes cylinder service, hydraulic pump and motor repair, manual-release valve replacement, and sender testing. Tru-Course sections address cable drums, assembly alignment, and steering adjustment.

The illustrations include an OMC stern-drive sectional view, the instrument-and-switch wiring diagram, and the SelecTrim wiring layouts. Functional tilt-circuit and trim-circuit diagrams support electrical tracing, while centrifugal spark-advance charts provide engine-specific tuning references.

Marine powertrain maintenance involves significant mechanical risks, particularly when handling heavy engine blocks or fuel-system components. Always apply standard shop safety practices. Consider consulting a certified technician before attempting complex diagnostic work on these systems.

Examples of Valve-Guide and Trim-Sender Specifications

The GMC in-line cylinder-head section gives valve-guide wear limits of 0.001" for intake guides and 0.002" for exhaust guides. These accompany the guide-inspection discussion and are distinct from the engine-specific production-clearance tables.

The SelecTrim sender test in the Ford V8 hydraulic-system section specifies 33.5 ohms at the LO position and 240 ohms at HI. The same section connects sender-circuit faults with persistent high or low gauge indications.