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Wisconsin AKS Engine

The Wisconsin AKS engine is a heavy-duty, single-cylinder, four-cycle, air-cooled industrial engine manufactured by the Wisconsin Motor Corporation
between 1939 and 1955. Designed as the specialized, high-speed variant of the standard Model AK, the AKS was engineered to deliver reliable mechanical power at elevated operating speeds for demanding equipment such as agricultural tillers, small compactors, generators, and industrial air compressors. The engine features a robust cast-iron block construction built to withstand continuous operations under varying field loads.

The engine utilizes an L-head (side-valve) configuration. Both the intake and exhaust valves are arranged vertically on one side of the cylinder block, operating parallel to the cylinder bore. The valves are driven directly by a gear-driven camshaft located within the crankcase, simplifying the valvetrain architecture and reducing overhead mechanical complexity. The cylinder architecture features a bore of 2-7/8 inches (73.0 mm) and a stroke of 2-3/4 inches (69.8 mm). This oversquare configuration supports the higher engine speeds by keeping piston speeds within reliable limits.

Fuel System: The fuel delivery architecture consists of a side-draft or up-draft carburetor (typically manufactured by Zenith or Tillotson) supplied from a 1-gallon fuel tank. Fuel flows through an inline sediment bowl fuel strainer before entering the carburetor bowl. Engine speed and fuel-air mixture delivery are mechanically regulated by a centrifugal flyball-type governor. The governor automatically adjusts the throttle valve opening to match changing engine loads and maintain targeted operating RPM. The system is rated to run on standard gasoline with an octane rating of 74 or higher.

Engine lubrication is managed via a constant-level splash type system. An internal mechanical plunger pump distributes oil to a constant-level trough located directly under the connecting rod cap. As the crankshaft rotates, a dipper on the connecting rod splashes oil from the trough to lubricate internal bearings, the camshaft, and the cylinder wall. Cooling is accomplished using a forced-induction air-cooled system. A combination fan-flywheel draws ambient air and forces it through a system of integrated sheet-metal shrouds, air ducts, and baffle plates. This managed airflow is directed across the deeply finned surfaces of the cylinder block and cylinder head to ensure uniform heat dissipation.

General Technical Data

Engine Specifications

Engine Model ............... Wisconsin AKS
Engine Type ............... 4-cycle single-cylinder L-head air-cooled gasoline engine
Number of Cylinders ............... 1
Engine Bore, in (mm) ............... 2.875 (73.03)
Engine Stroke, in (mm) ............... 2.750 (69.85)
Displacement, cu.in (cc) ............... 17.80 (291.69)
Rated Power at 2400 rpm, hp (kW) ............... 3.80 (2.83)
Rated Power at 3000 rpm, hp (kW) ............... 4.60 (3.43)
Rated Power at 3600 rpm, hp (kW) ............... 5.00 (3.73)
Maximum Torque, lb-ft (Nm) ............... 8.40 (11.39) at 2200 rpm
Low Idle Speed, rpm ............... 1000-1200
Max Operating Speed, rpm ............... 3600
Compression Ratio ............... 5.1:1
Valve Configuration ............... Side valve L-head design
Exhaust Valve Material ............... Heat-resistant Stellite alloy optional
Muffler Type ............... Direct-mount industrial canister style
Crankshaft Rotation ............... Clockwise when viewing from flywheel blower end
Camshaft Type ............... Gear-driven with integral lobes and fuel pump eccentric
Cylinder Block Material ............... Cast iron alloy
Cylinder Head Material ............... Cast iron
Crankcase Material ............... Cast iron integrated with block
Piston Material ............... Cast iron or aluminum alloy
Lubrication System ............... Splash system with plunger pump
Oil Pump Type ............... Plunger pump driven by camshaft eccentrics
Cooling System ............... Forced air-cooled via flywheel blower fan
Air Shroud Material ............... Heavy gauge pressed sheet steel
Air Cleaner Type ............... Heavy-duty oil bath or optional dry element
Ignition System ............... High tension magneto with automatic impulse coupling
Magneto Models ............... Wico XH-2531 or Fairbanks-Morse FMX1-2B7
Starting System ............... Rope start with pulley or manual hand crank

Fuel System

Carburetor Manufacturer ............... Zenith or Tillotson options
Carburetor Type ............... Updraft single-barrel configuration with manual choke
Carburetor Venturi Size, in (mm) ............... 0.750 (19.05)
Main Jet Type ............... Adjustable needle valve style
Idle Jet Type ............... Fixed with air bypass adjustment screw
Choke Valve Control ............... Manual cable or lever system
Throttle Valve Control ............... Linkage from mechanical centrifugal governor
Fuel Delivery Method ............... Gravity feed or mechanical diaphragm pump
Fuel Pump Type ............... Mechanical diaphragm actuated by camshaft lobe
Fuel Pump Operating Pressure, psi (kPa) ............... 1.5-3.0 (10.3-20.7)
Governor Type ............... Flyball mechanical centrifugal governor
Governor Location ............... Internal crankcase assembly gear driven
Fuel Tank Material ............... Heavy gauge stamped steel or tin plated steel
Fuel Strainer Type ............... Sediment bowl with fine mesh screen and shut-off valve
Fuel Line Material ............... Copper tubing or flexible fuel-resistant hose
Fuel Line Outer Diameter, in (mm) ............... 0.250 (6.35)
Fuel Recommended Rating ............... 90 octane minimum regular gasoline
Carburetor Float Level Setting, in (mm) ............... 1.125 (28.58)
Carburetor Float Needle Type ............... Viton tipped or solid brass option
Air-Fuel Ratio Range ............... 12.5:1 to 14.7:1
Choke Lever Operating Travel, in (mm) ............... 0.500 (12.70)
Governor Linkage Rod Diameter, in (mm) ............... 0.125 (3.18)
Fuel Tank Cap Type ............... Vented steel cap with internal baffle

Dimensions and Weight

Overall Height, in (mm) ............... 19.5 (495)
Overall Width, in (mm) ............... 16.3 (415)
Overall Length, in (mm) ............... 15.7 (400)
Dry Weight, lbs (kg) ............... 78 (35.4)
Shipping Weight, lbs (kg) ............... 92 (41.7)

Maintenance Data

Service Information

Compression Pressure Minimum, psi (kPa) ............... 75 (517)
Spark Plug Type ............... Champion D16 or equivalent
Ignition Timing, deg BTDC ............... 20
Breaker Point Gap, in (mm) ............... 0.015 (0.381)
Spark Plug Gap, in (mm) ............... 0.030 (0.762)
Intake Valve Tappet Clearance (Cold), in (mm) ............... 0.006 (0.152)
Exhaust Valve Tappet Clearance (Cold), in (mm) ............... 0.008 (0.203)

Engine Oil

Engine Oil Type .................. SAE 30, SAE 20W, or SAE 10W
API Service Classifications ......................... SE, SF, SG, or CC
Crankcase Oil Capacity, qt (L) ............... 1.00 (0.95)
Air Cleaner Oil Capacity, pt (L) ............... 0.25 (0.12)
Clutch Housing Oil Capacity, pt (L) ............... 0.50 (0.24)
Reduction Gear Box Oil Capacity, pt (L) ............... 0.75 (0.35)

Service Intervals

Change engine oil ............... Every 50 hours
Inspect air cleaner ............... Every 8 hours
Service air cleaner ............... Every 50 hours
Clean fuel strainer ............... Every 50 hours
Valve clearance adjustment ............... Every 150 hours
Fuel system inspection ............... Every 100 hours
Clean spark plug ............... Every 100 hours
Replace spark plug ............... Every 300 hours
Clean cooling fin ............... Every 50 hours
Flush/Clean fuel tank ............... Every 500 hours
Change reduction gear oil ............... Every 500 hours

Service Specifications

Cylinder Bore Inside Diameter, in (mm) ............... 2.875-2.876 (73.025-73.050)
Cylinder Bore Maximum Out of Round, in (mm) ............... 0.002 (0.051)
Cylinder Bore Maximum Taper, in (mm) ............... 0.003 (0.076)
Crankpin Journal Diameter, in (mm) ............... 1.375 (34.93)
Main Journal Diameter (Blower End), in (mm) ............... 1.181 (30.00)
Main Journal Diameter (Drive End), in (mm) ............... 1.378 (35.00)
Connecting Rod Journal Clearance, in (mm) ............... 0.0010-0.0025 (0.025-0.064)
Connecting Rod Side Play Clearance, in (mm) ............... 0.005-0.010 (0.127-0.254)
Crankshaft End Play, in (mm) ............... 0.002-0.004 (0.051-0.102)
Crankshaft Journal Out of Round, in (mm) ............... 0.001 (0.025)
Piston Outside Diameter Standard, in (mm) ............... 2.872 (72.95)
Piston to Cylinder Wall Clearance, in (mm) ............... 0.0035-0.0045 (0.089-0.114)
Piston Pin Outside Diameter, in (mm) ............... 0.625 (15.88)
Piston Pin to Piston Pin Bore Clearance, in (mm) ............... 0.0001-0.0005 (0.003-0.013)
Piston Pin to Con Rod Bushing Clearance, in (mm) ............... 0.0004-0.0009 (0.010-0.023)
Top Ring End Gap, in (mm) ............... 0.0070-0.0150 (0.178-0.381)
Second Ring End Gap, in (mm) ............... 0.0070-0.0150 (0.178-0.381)
Third Ring End Gap, in (mm) ............... 0.0070-0.0150 (0.178-0.381)
Oil Ring End Gap, in (mm) ............... 0.0070-0.0170 (0.178-0.431)
Top Ring Groove Side Clearance, in (mm) ............... 0.0020-0.0035 (0.051-0.089)
Second Ring Groove Side Clearance, in (mm) ............... 0.0015-0.0030 (0.038-0.076)
Third Ring Groove Side Clearance, in (mm) ............... 0.0015-0.0030 (0.038-0.076)
Oil Ring Groove Side Clearance, in (mm) ............... 0.0015-0.0030 (0.038-0.076)
Intake Valve Head Diameter, in (mm) ............... 1.187 (30.15)
Exhaust Valve Head Diameter, in (mm) ............... 1.062 (26.97)
Intake Valve Stem Outside Diameter, in (mm) ............... 0.3100-0.3105 (7.874-7.887)
Exhaust Valve Stem Outside Diameter, in (mm) ............... 0.3085-0.3095 (7.836-7.861)
Intake Valve Stem to Guide Clearance, in (mm) ............... 0.002-0.0035 (0.051-0.089)
Exhaust Valve Stem to Guide Clearance, in (mm) ............... 0.003-0.005 (0.076-0.127)
Valve Guide Inside Diameter, in (mm) ............... 0.3125 (7.938)
Valve Face Angle, degrees ............... 45
Valve Seat Angle, degrees ............... 45
Valve Seat Width, in (mm) ............... 0.045-0.060 (1.14-1.52)
Valve Spring Free Length, in (mm) ............... 1.625 (41.28)
Camshaft Journal Diameter, in (mm) ............... 0.625 (15.88)
Camshaft Journal Clearance, in (mm) ............... 0.0015-0.0030 (0.038-0.076)
Camshaft End Play, in (mm) ............... 0.002-0.006 (0.051-0.152)
Camshaft Timing Gear Backlash, in (mm) ............... 0.002-0.004 (0.051-0.102)

Tightening Torques

Cylinder Head Bolts, lb-ft (Nm) ............... 22-24 (29.8-32.5)
Connecting Rod Cap Bolts, lb-ft (Nm) ............... 18-20 (24.4-27.1)
Flywheel Nut, lb-ft (Nm) ............... 60-65 (81.3-88.1)
Main Bearing Cap Screws, lb-ft (Nm) ............... 14-16 (19.0-21.7)
Crankcase Base Cover Bolts, lb-ft (Nm) ............... 10-12 (13.6-16.3)
Magneto Mounting Cap Screws, lb-ft (Nm) ............... 14-16 (19.0-21.7)
Spark Plug, lb-ft (Nm) ............... 24-28 (32.5-37.9)
Camshaft Thrust Plate Screws, lb-in (Nm) ............... 60-70 (6.8-7.9)
Governor Lever Clamp Bolt, lb-in (Nm) ............... 45-55 (5.1-6.2)
Air Shroud Retaining Screws, lb-in (Nm) ............... 45-55 (5.1-6.2)
Carburetor Mounting Nuts, lb-ft (Nm) ............... 10-12 (13.6-16.3)
Intake/Exhaust Manifold Stud Nuts, lb-ft (Nm) ............... 14-16 (19.0-21.7)
Muffler Pipe Thread Connection, lb-ft (Nm) ............... 25-35 (33.9-47.5)
Fuel Pump Mounting Bolts, lb-in (Nm) ............... 70-90 (7.9-10.2)
Oil Base Drain Plug, lb-ft (Nm) ............... 15-20 (20.3-27.1)
Breaker Point Mounting Screw, lb-in (Nm) ............... 15-20 (1.7-2.3)
Condenser Mounting Screw, lb-in (Nm) ............... 15-20 (1.7-2.3)
Magneto Ground Terminal Nut, lb-in (Nm) ............... 10-15 (1.1-1.7)
Flywheel Shroud Plate Bolts, lb-in (Nm) ............... 45-55 (5.1-6.2)
Oil Pump Trough Assembly Screws, lb-in (Nm) ............... 60-75 (6.8-8.5)
Governor Housing Cover Screws, lb-in (Nm) ............... 60-75 (6.8-8.5)
Valve Inspection Cover Nut, lb-ft (Nm) ............... 6-8 (8.1-10.8)
Starting Pulley Mounting Bolts, lb-ft (Nm) ............... 14-16 (19.0-21.7)
Air Cleaner Mounting Bracket Bolts, lb-ft (Nm) ............... 10-12 (13.6-16.3)
Clutch Housing Mounting Screws, lb-ft (Nm) ............... 22-26 (29.8-35.3)
Reduction Gear Case Fasteners, lb-ft (Nm) ............... 18-22 (24.4-29.8)
Fan Pulley Drive Pinion Screw, lb-ft (Nm) ............... 12-15 (16.3-20.3)
Breather Assembly Retaining Nut, lb-in (Nm) ............... 35-45 (4.0-5.1)
Fuel Tank Straps Clamp Bolts, lb-in (Nm) ............... 40-50 (4.5-5.6)

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• Wisconsin Engines Specs
  
• Wisconsin AEN Specs
  
• Wisconsin AENL Specs
  
• Wisconsin AENLD Specs
  
• Wisconsin AGND Specs
  
• Wisconsin AKN Specs
  
• Wisconsin BKN Specs
  

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