1952 Mercury 10 HP Mark 15 Outboard Specs & Part Numbers
Technical Guide: 1952 Mercury 10 HP Mark 15 Outboard Motor
The 1952 Kiekhaefer Mercury Mark 15 is a legendary piece of American marine engineering. Known as a “Super 10,” this motor was part of the transitional post-war era where Carl Kiekhaefer’s company revolutionized the outboard industry with high-RPM, lightweight, and incredibly durable alternate-firing twins. This guide provides comprehensive technical specifications, maintenance procedures, and historical context for restoring or servicing this classic motor.
Overview & Specifications
The Mark 15 utilizes the famous 19.84 cubic inch “Hurricane” series powerhead. Unlike its direct-drive predecessors (like the KF7 and KG7), the Mark 15 introduced a neutral-clutch mechanism, making it far more user-friendly for docking and starting.
| Specification | Value / Detail |
|---|---|
| Manufacturer | Kiekhaefer Mercury (Fond du Lac, Wisconsin) |
| Model Year | 1952 |
| Horsepower Rating | 10.0 HP @ 4800 RPM |
| Engine Type | Alternate-firing 2-cylinder, 2-stroke |
| Displacement | 19.84 cu. in. (325 cc) |
| Bore x Stroke | 2.125 in. x 1.400 in. |
| Fuel/Oil Ratio | 16:1 (1/2 pint of TC-W3 or vintage-certified non-detergent SAE 30 oil per gallon of regular unleaded gasoline) |
| Weight | Approx. 64 lbs. (29 kg) |
| Carburetor | Tillotson AJ-39A (or AJ-41A depending on production run) |
Common Maintenance & Tune-up Specs
Restoring a vintage Mark 15 to running condition requires precise adjustments to the ignition and fuel delivery systems. Below are the critical tune-up tolerances and part profiles.
Ignition System
- Magneto Type: Bendix-Scintilla or Phelon (Bendix-Scintilla is most common on 1952 Mark 15s).
- Spark Plugs: Champion J8C (Modern equivalent: Champion 841 / J8C).
- Spark Plug Gap:
0.025 inches (0.63 mm) - Breaker Point Gap:
0.020 inches (0.51 mm) - Timing: Timing is set by aligning the stator plate sweep with the throttle linkage cam. Ensure the points break exactly at the “MAX” timing mark on the flywheel when at full throttle.
Carburetor Tuning (Tillotson AJ Series)
- High-Speed Needle (Top): Start by gently seating the needle, then back it out 1-1/2 turns. Adjust under load at wide-open throttle until the engine runs smoothly without bogging (too lean) or four-stroking (too rich).
- Low-Speed/Idle Needle (Bottom): Start at 1 turn open from gently seated. Adjust with the motor warm in forward gear at slow idle speed until a crisp transition to throttle is achieved.
Cooling & Gearcase Maintenance
- Water Pump Impeller: Located on the driveshaft above the gearcase housing. These motors use a flexible rubber impeller. If the motor has sat unused, always replace this impeller before running to prevent catastrophic overheating.
- Gearcase Lubricant: Use a high-quality, non-corrosive marine gear lube (such as Lubriplate 105 or a vintage-safe SAE 90 hypoid gear oil). Do not use modern high-viscosity synthetic lubes containing sulfur additives that can damage yellow metals (bronze bushings) inside the gearcase.
- Gearcase Fill Process: Fill from the lower drain screw hole until grease/oil expels from the upper vent screw hole to prevent air pockets.
Notable Features & History
The “Full Jewel” Powerhead
Carl Kiekhaefer’s obsession with durability led to the implementation of anti-friction ball and roller bearings on every rotating journal in the motor—including the crankshaft main bearings, crankpins, and wrist pins. Mercury marketed this as the “Full Jewel Powerhead.” This costly design allowed the Mark 15 to safely spin at much higher RPMs than its contemporary competitors from OMC (Evinrude/Johnson), which still relied heavily on bronze sleeve bushings.
The Neutral Clutch
Unlike modern outboards with a full Forward-Neutral-Reverse (F-N-R) gearshift gearcase, the 1952 Mark 15 featured a unique dry disc clutch mechanism in the driveshaft housing. This allowed the operator to start the engine in “Neutral” without turning the propeller. Engaging the lever on the side of the tower locked the clutch plates, transferring power to the propeller. To reverse, the operator simply rotated the entire motor 180 degrees using the steering handle.
The Hurricane Heritage
The Mark 15 inherited its internal porting design from the legendary KG7 “Super 10” racing engines. It featured reed-valve induction through the crankcase and highly efficient loop scavenging. This gave the motor an incredibly power-to-weight ratio and a distinctive, aggressive exhaust note that earned it a dedicated following among post-war utility class racers and sport boaters alike.