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Wisconsin AKN Engine

The Wisconsin AKN is a heavy-duty, single-cylinder, four-cycle, horizontal-shaft internal combustion engine produced by the Wisconsin Motor Corporation. Introduced in 1949 as a high-compression, upgraded counterpart to the earlier AK series, the AKN block is engineered explicitly for demanding industrial, agricultural, and construction equipment. It features a cast-iron cylinder block and crankcase assembly designed to provide exceptional structural integrity and massive low-end lugging torque under sustained load profiles.

The engine is widely recognized for its robust, industrial-grade reliability and modular versatility across auxiliary machinery. The cylinder head utilizes an L-head (side-valve) configuration. Valves are arranged vertically on one side of the cylinder block, actuated directly by the camshaft via mechanical tappets. Cylinder Bore: 2-7/8 inches (73.03 mm). Piston Stroke: 2-3/4 inches (69.85 mm). Total Displacement: Approximately 17.8 cubic inches (291.7 cc).

Engine lubrication utilizes a constant-level splash system. A cam-driven, plunger-type internal oil pump draws oil from the base reservoir and pumps it at a steady rate into a calibrated oil trough situated directly below the connecting rod journal. An oil dipper integrated into the connecting rod cap splashes the lubricant, misting internal components. The engine features a forced-air cooling mechanism. Airflow is generated via a combination fan-flywheel encased within a rigid sheet-metal air shroud. Integrated sheet-metal ducts and baffle plates segment and force the air stream directly across the external cooling fins of the cylinder block and cylinder head to ensure uniform temperature control.

Fuel delivery is governed by a gravity-fed or fuel-pump assisted gasoline layout featuring a standard 1-gallon fuel tank and inline sediment strainers. Air-fuel atomization is handled by a single-barrel balanced carburetor: typically manufactured by Zenith, Marvel-Schebler, or Stromberg. Engine speed regulation is achieved via a centrifugal flyball-type mechanical governor that acts directly on the throttle butterfly valve to mechanically adjust to external loading variations. The minimum recommended fuel octane rating required to prevent internal engine detonation or scoring is 74.

General Technical Data

Engine Specifications

Engine Model ............... Wisconsin AKN
Engine Type ............... 4-cycle single-cylinder L-head air-cooled gasoline engine
Number of Cylinders ............... 1
Engine Bore, in (mm) ............... 2.87 (73.03)
Engine Stroke, in (mm) ............... 2.75 (69.85)
Displacement, cu.in (cc) ............... 17.8 (291.7)
Rated Power at 1600 rpm, hp (kW) ............... 3.2 (2.39)
Rated Power at 2000 rpm, hp (kW) ............... 4.2 (3.13)
Rated Power at 2400 rpm, hp (kW) ............... 5.0 (3.73)
Rated Power at 3000 rpm, hp (kW) ............... 5.7 (4.25)
Rated Power at 3600 rpm, hp (kW) ............... 6.2 (4.62)
Maximum Power, hp (kW) ............... 6.2 (4.62)
High Idle Speed, rpm ............... 3800
Governed Speed Setting, rpm ............... 3600
Low Idle Speed Range, rpm ............... 1000-1200
Compression Ratio ............... 5.5:1 to 6.0:1
Cylinder Block Material ............... High-tensile cast iron
Cylinder Head Material ............... Cast aluminum alloy or heavy duty cast iron
Crankcase Material ............... Heavy cast iron integrated with cylinder barrel
Connecting Rod Material ............... High-tensile drop-forged aluminum alloy or forged steel
Crankshaft Material ............... Heat-treated drop-forged counterbalanced steel alloy
Camshaft Type ............... Forged steel hardened lobes with integrated gear drive
Valve Configuration ............... L-head side valve structure in block side chamber
Valve Mechanism ............... Direct mechanical lifter tappet actuation
Lubrication Method ............... Splash system with oil pump plunger combination
Cooling System ............... Forced air-cooled via flywheel blower shroud
Air Cleaner Element ............... Oil bath mesh type or dry paper cartridge element
Ignition System ............... High-tension magneto ignition device

Fuel System

Fuel Induction Delivery Type ............... Gravity flow feed or mechanical diaphragm pump
Carburetor Manufacturer Options ............... Zenith or Marvel-Schebler
Carburetor Model Variant ............... Zenith 61S5 or Marvel-Schebler VH12-VH14
Carburetor Throat Venturi Diameter, in (mm) ............... 0.625 (15.875)
Governor System ............... Flyball centrifugal mechanical weight type built-in
Fuel Tank Capacity Capacity (Std), gal (L) ............... 1.00 (3.79)
Fuel Tank Capacity Capacity (Opt), gal (L) ............... 1.50 (5.68)
Fuel Strainer Unit Component ............... Glass sediment bowl with screen mesh
Fuel Pump Delivery Pressure Range, psi (bar) ............... 1.50-2.50 (0.103-0.172)
Fuel Pump Primer Feature ............... Manual prime lever built into pump casing
Carburetor Main Needle Valve Setting ............... 1.25-1.50 turns open from closed position
Carburetor Idle Needle Valve Setting ............... 1.00-1.25 turns open from closed position
Recommended Fuel Grade Octane Level ............... 70 minimum non-leaded regular gasoline
Fuel Tank Vent Hole Location ............... Integrated into threaded fuel filler cap
Carburetor Float Level Distance Upper Rim to Float, in (mm) ............... 0.250 (6.350)
Carburetor Float Drop Distance Maximum Extension, in (mm) ............... 0.4375 (11.112)
Carburetor Throttle Shaft Bushing I.D in (mm) ............... 0.251 (6.375)
Fuel Delivery Control Shut-Off Device ............... Brass needle cock built into sediment bowl base
Air Intake Silencer Fitting Pipe Diameter, in (mm) ............... 1.250 (31.750)

Dimensions and Weight

Overall Height, in (mm) ............... 21.4 (545)
Overall Width, in (mm) ............... 16.5 (420)
Overall Length, in (mm) ............... 15.3 (390)
Dry Weight, lbs (kg) ............... 76 (34.5)
Shipping Weight, lbs (kg) ............... 95 (43)

Maintenance Data

Service Information

Compression Pressure at Cranking Speed, psi (bar) ............... 70.0-85.0 (4.8-5.7)
Minimum Acceptable Compression Pressure, psi (bar) ............... 60.0 (4.14)
Spark Plug Reach, in (mm) ............... 0.50 (12.70)
Spark Plug Gap, in (mm) ............... 0.03 (0.76)
Breaker Point Gap, in (mm) ............... 0.02 (0.51)
Ignition Timing ............... 28 deg BTDC
Inlet Valve Clearance, Cold, in (mm) ............... 0.0080 (0.203)
Exhaust Valve Clearance, Cold, in (mm) ............... 0.0140 (0.355)

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 (0.946)
Oil Bath Air Cleaner Capacity, pt (L) ............... 0.25 (0.118)

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) ............... 2.8750-2.8760 (73.025-73.050)
Cylinder Bore Maximum Out-of-Round, in (mm) ............... 0.0010 (0.025)
Cylinder Bore Maximum Taper, in (mm) ............... 0.0025 (0.063)
Crankshaft Main Journal Outside Diameter, in (mm) ............... 1.3750-1.3755 (34.925-34.938)
Crankshaft Main Journal Out-of-Round, in (mm) ............... 0.0005 (0.012)
Crankshaft Crankpin Journal Diameter, in (mm) ............... 1.3750-1.3755 (34.925-34.938)
Crankshaft Bearing End Playl, in (mm) ............... 0.0010-0.0040 (0.025-0.101)
Connecting Rod Big End Bore Inside Diameter, in (mm) ............... 1.5005-1.5010 (38.112-38.125)
Connecting Rod Journal Clearance, in (mm) ............... 0.0008-0.0022 (0.020-0.055)
Connecting Rod Side Clearance, in (mm) ............... 0.0040-0.0100 (0.101-0.254)
Piston-to-Cylinder Wall Clearance, in (mm) ............... 0.0035-0.0045 (0.089-0.114)
Piston Pin Bore Inside Diameter, in (mm) ............... 0.6251-0.6254 (15.877-15.885)
Piston Pin Outside Diameter, in (mm) ............... 0.6248-0.6250 (15.870-15.875)
Piston Pin-to-Piston Pin Bore Clearance, in (mm) ............... 0.0001-0.0006 (0.002-0.015)
Piston Pin-to-Small End Bushing Clearance, in (mm) ............... 0.0005-0.0011 (0.012-0.028)
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)
Cylinder Head Deck Flatness Maximum Warpage, in (mm) ............... 0.0030 (0.0762)
Inlet Valve Stem Outside Diameter, in (mm) ............... 0.3110-0.3115 (7.899-7.912)
Exhaust Valve Stem Outside Diameter, in (mm) ............... 0.3105-0.3110 (7.886-7.899)
Inlet Valve Guide Inside Diameter, in (mm) ............... 0.3125-0.3135 (7.937-7.962)
Exhaust Valve Guide Inside Diameter, in (mm) ............... 0.3125-0.3135 (7.937-7.962)
Inlet Valve Stem-to-Guide Clearance, in (mm) ............... 0.0010-0.0025 (0.025-0.063)
Exhaust Valve Stem-to-Guide Clearancet, in (mm) ............... 0.0015-0.0030 (0.038-0.076)
Valve Face Angle, degrees ............... 45
Valve Seat Angle, degrees ............... 45
Valve Seat Width, in (mm) ............... 0.0450 (1.143)
Valve Spring Free Length, in (mm) ............... 1.6250 (41.275)
Camshaft Journal Bearing Diameter, in (mm) ............... 0.7500-0.7505 (19.050-19.062)
Camshaft Radial Clearance, in (mm) ............... 0.0015-0.0030 (0.038-0.076)
Camshaft End Play, in (mm) ............... 0.0020-0.0060 (0.051-0.152)
Camshaft Lobe Height (Inlet), in (mm) ............... 1.1250 (28.5750)
Camshaft Lobe Height (Exhaust), in (mm) ............... 1.1250 (28.5750)
Tappet Barrel Outside Diameter, in (mm) ............... 0.4985-0.4990 (12.661-12.674)
Tappet Crankcase Guide Hole Diameter, in (mm) ............... 0.5000-0.5010 (12.700-12.725)

Tightening Torques

Cylinder Head Nuts, lb-ft (Nm) ............... 22.0-24.0 (29.8-32.5)
Connecting Rod Cap Bolts, lb-ft (Nm) ............... 18.0-22.0 (24.4-29.8)
Flywheel Retention Nut, lb-ft (Nm) ............... 60.0-70.0 (81.3-94.9)
Crankcase Cover Flange Nuts, lb-ft (Nm) ............... 12.0-14.0 (16.3-18.9)
Spark Plug, lb-ft (Nm) ............... 25.0-30.0 (33.9-40.6)
Magneto Mounting Flange Base Bolt, lb-ft (Nm) ............... 14.0-18.0 (18.9-24.4)
Governor Housing Cap Screw, lb-ft (Nm) ............... 8.0-10.0 (10.8-13.5)
Air Intake Mounting Flange Bolt, lb-ft (Nm) ............... 8.0-10.0 (10.84-13.5)
Exhaust Manifold Mating Block Screws, lb-ft (Nm) ............... 14.0-18.0 (18.9-24.4)
Fuel Tank Bracket Attachment Bolts, lb-ft (Nm) ............... 10.0-12.0 (13.5-16.3)
Oil Drain Plug, lb-ft (Nm) ............... 20.0-25.0 (27.1-33.9)
Oil Pump Base Cover Screw, lb-ft (Nm) ............... 6.0-8.0 (8.1-10.8)
Air Shroud Shield Cover Housing Screws, lb-ft (Nm) ............... 5.0-7.0 (6.7-9.5)
Valve Inspection Service Chamber Nut, lb-ft (Nm) ............... 4.0-6.0 (5.4-8.1)
Crankshaft PTO Drive Pulley Screw, lb-ft (Nm) ............... 12.0-15.0 (16.3-20.3)
Breaker Point Box Contact Screw, lb-in (Nm) ............... 15.0-20.0 (1.7-2.2)
Condenser Core Wire Terminal Screws, lb-in (Nm) ............... 10.0-15.0 (1.1-1.7)
Fuel Pump Mating Pad Mounting Studs, lb-ft (Nm) ............... 12.0-14.0 (16.3-18.9)
Governor Lever Arm Pinch Bolt, lb-in (Nm) ............... 35.0-45.0 (3.9-5.1)
Air Cleaner Mounting Bracket Ring Clamp, lb-in (Nm) ............... 20.0-30.0 (2.3-3.4)
Flywheel Magneto Stator Plate Holding Fasteners, lb-ft (Nm) ............... 8.0-10.0 (10.8-13.5)
Crankcase Base Foot Plate Bolts, lb-ft (Nm) ............... 25.0-30.0 (33.9-40.6)
Muffler Locking Collar Pipe Exhaust Ring, lb-ft (Nm) ............... 35.0-45.0 (47.4-61.0)
Breather Assembly Capscrew, lb-ft (Nm) ............... 6.0-8.0 (8.1-10.8)

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

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