1966 Johnson 6 HP Sea-Horse Outboard Specs & Part Numbers
The 1966 Johnson 6 HP Sea-Horse (Model CD-23 / CDS-23) is a legendary twin-cylinder outboard motor engineered during the golden era of Outboard Marine Corporation (OMC). Renowned for its reliability, portability, and smooth idling capabilities, this vintage motor remains a favorite among collectors, restorers, and small-boat anglers today.
Overview & Technical Specifications
The 1966 CD-23 is a water-cooled, loop-scavenged, two-stroke outboard engine. It features a full gearshift (Forward-Neutral-Reverse) and was designed to run on a modern 50:1 fuel-to-oil mixture, a transition OMC made across its lineup in 1964 due to the introduction of needle bearings throughout the powerhead.
| Engine Overview | |
|---|---|
| Manufacturer | Outboard Marine Corporation (OMC) / Johnson Outboards |
| Model Year | 1966 |
| Model Numbers | CD-23 (Standard Shaft), CDS-23 (Electric Start Option) |
| Horsepower | 6.0 HP @ 4,500 RPM |
| Cylinders | 2 (Inline, alternate firing) |
| Displacement | 8.84 cu. in. (145 cc) |
| Bore x Stroke | 1.875″ x 1.600″ (47.63 mm x 40.64 mm) |
| Fuel Mix Ratio | 50:1 (Regular unleaded gas to TC-W3 2-stroke outboard oil) |
| Recommended Fuel | 87 Octane (Non-Ethanol/Rec 90 highly recommended) |
| Dry Weight | 51 lbs (23.1 kg) |
Common Maintenance & Tune-Up Specifications
Keeping a vintage Sea-Horse running smoothly requires regular attention to its ignition system, carburetor, and cooling system. Below are the critical tune-up tolerances and part numbers for servicing the 1966 model.
| Tune-Up & Ignitition Specs | |
|---|---|
| Spark Plugs | Champion J6C (or Champion J4C for sustained high-speed run times) |
| Spark Plug Gap | 0.030 inches (0.76 mm) |
| Ignition System Type | OMC Universal Magneto (Under flywheel) |
| Points Gap | 0.020 inches (0.51 mm) at high lobe of cam |
| Condenser Capacity | 0.18 to 0.22 microfarads (mfd) |
| Carburetor Low-Speed Needle | Initial setting: 1.5 turns open from gently seated |
| Carburetor High-Speed Jet | Fixed Orifice (No adjustable high-speed needle on this model) |
| Thermostat | Opens at 143°F (61.6°C) |
| Gearcase Lubricant | OMC/BRP Hi-Vis or any quality marine 80W-90 Outboard Gear Lube |
| Water Pump Impeller Part No. | OMC Part: 379766 / Sierra: 18-3001 |
Ignition System Service Tips
The 1966 Johnson 6 HP uses the famous OMC Universal Magneto system. If you are experiencing weak or no spark, address the following common failure points:
- Cracked Coils: The original green plastic coils used by OMC in this era are notorious for cracking over time, allowing moisture to enter and short-out the windings. If your coils are original, cracked, or showing signs of swelling, replace them with modern black epoxy replacements.
- Breaker Points: Ensure the points are free of oil and oxidation. Clean the contact faces with a piece of clean cardstock dipped in lacquer thinner, then set the gap to exactly 0.020 inches when the rubbing block is on the “TOP” mark of the flywheel cam.
Lower Unit & Water Pump Maintenance
Because these motors often sit for long periods, water pump impellers dry out and dry-rot. Operating the motor with a degraded impeller can quickly lead to overheating and catastrophic powerhead damage.
- Impeller Replacement: The lower unit must be dropped to service the water pump. Access the shift-rod connector through the small oval plate on the side of the exhaust housing. Remove only the lower bolt of the brass connector to release the lower unit.
- Gearcase Seals: When changing the gear oil, check for a milky appearance. If the oil is white/cloudy, water is entering the gearcase. The most common entry points are the propeller shaft seal, the drive shaft seal under the water pump, or the tiny O-ring on the shift rod.
Notable Features & History
The Legacy of the CD Series
The “CD” series of 5.5 HP and 6 HP outboards began in the mid-1950s and evolved continuously through 1979. By 1966, Johnson had perfected this small displacement powerhead. The 1966 model represented a sweet spot of engineering: it featured the modern fiberglass “clamshell” cowl design, which made the motor significantly quieter than its 1950s metal-hooded predecessors, and was far lighter than modern 4-stroke outboards of equivalent horsepower.
Key Design Milestones of the 1966 CD-23
- Isolation Mount Suspension: OMC equipped this motor with an engineered system of rubber dampening mounts. This significantly reduced vibration transferred to the tiller handle and the boat’s transom, earning it the reputation of a whisper-quiet trolling motor.
- Thermostatically Controlled Cooling: Unlike basic outboards that ran water straight through the head constantly, the 1966 model utilized a recirculating cooling system regulated by a 143°F thermostat. This allowed the engine to quickly reach and maintain optimum operating temperatures, drastically reducing spark plug fouling during prolonged idling or trolling.
- Shallow Water Drive: A manual tilt lever bracket allowed the operator to run the motor in a semi-tilted position, facilitating safe navigation through shallow, weedy, or rocky waters without damaging the gearcase.
Why it Remains a Classic
The 1966 Johnson 6 HP Sea-Horse is considered by many outboard mechanics to be one of the best small outboards ever built. Its simplicity means it can be completely overhauled with basic hand tools. Parts remain cheap and widely available due to the massive volume of these engines produced. For a boater looking for a reliable, vintage auxiliary engine or a lightweight power plant for a classic aluminum jon boat, the CD-23 remains an outstanding choice.