1963 Johnson 5.5 HP Sea-Horse Outboard Specs & Part Numbers
Technical Guide: 1963 Johnson 5.5 HP Sea-Horse (Model CD-20)
The 1963 Johnson Sea-Horse 5.5 HP (Model CD-20) is a legendary twin-cylinder outboard motor revered by vintage marine enthusiasts and fishermen alike. Known for its quiet operation, smooth trolling capabilities, and bulletproof reliability, this model represents the pinnacle of OMC’s (Outboard Marine Corporation) small twin engineering from the golden era of American outboards.
This technical guide provides comprehensive specifications, maintenance data, and historical context necessary to restore, maintain, and operate this classic outboard motor.
—
1. Overview & Technical Specifications
By 1963, Johnson had refined the 5.5 HP platform into a highly dependable, user-friendly utility motor. Crucially, the 1963 model utilizes a modern, single-line fuel pump system rather than the cumbersome dual-line pressurized fuel tanks used in early-1950s models.
| Parameter | Specification |
|---|---|
| Manufacturer | Johnson Motors (OMC) |
| Model Number | CD-20 / CDS-20 (Short Shaft / Long Shaft) |
| Horsepower | 5.5 HP @ 4,000 RPM |
| Engine Type | 2-Cylinder, 2-Stroke, Alternate Firing Twin |
| Displacement | 8.84 cubic inches (145 cc) |
| Bore & Stroke | 2.0625 in x 1.3281 in (52.4 mm x 33.7 mm) |
| Fuel-to-Oil Ratio | 24:1 (1 Quart TC-W3 oil to 6 gallons 87 Octane unleaded gasoline) |
| Fuel System | Single-line fuel pump, manual start, external tank |
| Starting System | Manual recoil starter |
| Dry Weight | Approx. 51 lbs (23 kg) |
—
2. Common Maintenance & Tune-Up Specifications
Keeping the 5.5 HP Sea-Horse running smoothly requires standard periodic maintenance. Below are the key clearance settings, plug requirements, and part details for a standard tune-up.
Ignition & Electrical System
The 1963 Sea-Horse utilizes the classic OMC Universal Magneto system, located beneath the flywheel. This system is simple to service but must be adjusted accurately for optimal performance.
- Spark Plug: Champion J6C (or modern equivalent Champion J8C if running hot/idling extensively)
- Spark Plug Gap: 0.030 inches (0.76 mm)
- Points Gap: 0.020 inches (0.51 mm) at high point of the cam
- Condenser Capacity: 0.18 to 0.22 microfarads (mfd)
- Ignition Coils: If the motor still has its original black or dark green plastic-coated coils, inspect them closely. These original casings are notorious for cracking, absorbing moisture, and failing. Replace them with modern epoxy-molded coils.
Carburetor & Fuel Delivery
The CD-20 features a dual-needle, float-feed carburetor with adjustable low-speed (idle) and high-speed (high-speed jet) mixtures.
- Initial High-Speed Needle Setting (Bottom Knob): Gently turn clockwise until fully seated, then turn counter-clockwise 3/4 to 1 turn.
- Initial Low-Speed/Idle Needle Setting (Top Knob): Gently turn clockwise until fully seated, then turn counter-clockwise 1-1/2 turns.
- Float Height: When inverted, the float arm should rest perfectly parallel to the gasket surface of the carburetor body.
Cooling & Gearcase Maintenance
| Component | Maintenance Action & Part Info |
|---|---|
| Impeller & Water Pump | Replace every 2-3 seasons. Uses OEM Impeller Part Number 277181 / 375688 (or Sierra 18-3001). Inspect the water pump housing cup for grooving; replace if scored. |
| Gearcase Lubricant | Use standard 80W-90 Marine Gear Lube (Hi-Vis). Fill from the bottom drain hole until it exits the top “vent” hole. |
| Thermostat | This model features a thermostat-controlled bypass system. Ensure the thermostat opens at 140°F (60°C). Replace if stuck open (motor runs too cold/rough idle) or stuck closed (overheating). |
—
3. Notable Features & History
The Johnson 5.5 HP “CD” series ran from 1954 through 1964, carving out a legendary reputation as a premium, quiet utility motor. The 1963 CD-20 represents the design’s peak maturity before the model was replaced by the 6 HP platform in 1965.
A Shift in Fuel Tank Engineering
In the mid-1950s, OMC outboards required a “pressure tank.” These systems pressurized the fuel tank via a pressure line from the crankcase to push fuel to the motor. By 1959, OMC transitioned these small outboards to standard, single-line suction fuel systems using a crankcase pulse-driven diaphragm fuel pump. The 1963 CD-20 features this modern system, making it highly desirable today because it operates safely with standard, modern portable marine fuel tanks.
Full Gearshift Capability
Unlike many light outboards of its era which required turning the entire motor 180 degrees to reverse, the CD-20 features a robust, full mechanical gearshift: Forward, Neutral, and Reverse (F-N-R). Combined with a steering friction damper and a co-pilot mechanism, this made it the ultimate trolling motor for fishermen.
Super Quiet Power (Sound-Deadening Design)
Johnson heavily marketed the “Sea-Horse Quietness” of this model. The entire powerhead is isolated on rubber mountings inside a sealed, cast aluminum lower cowl. Exhaust gas is routed down through the midsection housing and relieved underwater through the propeller hub/snout, keeping operating noise to a whisper. It was this quietness, combined with its buttery-smooth idling at low RPMs, that earned the CD-20 series the moniker of the “Fisherman’s Friend.”