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Wisconsin BKN Engine

The Wisconsin BKN engine is a heavy-duty, single-cylinder, four-cycle, air-cooled industrial engine manufactured by the Wisconsin Motor Corporation. Designed for extreme durability in demanding agricultural, industrial, and utility applications, this cast-iron power unit is engineered to deliver high torque and sustained output under continuous loads. It features a classic heavy flywheel design to maintain momentum and operates with a standard counter-clockwise rotation facing the power take-off shaft. It is widely recognized for its long operational lifecycle and robust construction.

The engine utilizes an L-head (flathead / side-valve) configuration. The valves are positioned in the cylinder block parallel to the cylinder bore rather than in the cylinder head. Valve tappets are non-adjustable; clearance adjustments require the mechanical removal and manual grinding of the valve stem base. The internal cylinder geometry features a 2-7/8 inch cylinder bore and a 2-3/4 inch piston stroke. This configuration yields a total engine displacement of 17.8 cubic inches (292 cc).

The fuel delivery architecture consists of a gravity-fed or pump-assisted balanced carburetor designed to supply uniform fuel-to-air ratios across variable engine speeds and loads. The system includes a standard fuel shut-off valve, an inline gasoline filter or sediment bowl strainer, and an oil-bath style air cleaner to isolate airborne contaminants. Ignition spark is delivered via a gear-driven, high-tension magneto with an impulse coupling that operates at crankshaft speed independently of an external battery source. While standard configurations consume standard gasoline, specialized adaptations allow the system to operate on alternative fuels like kerosene, LPG, or natural gas.

Engine lubrication is managed through a mechanical splash system fed by a internal oil pump. An oil dipper on the connecting rod distributes oil from the crankcase reservoir to the cylinder walls, piston pin, and internal bearings. Maintenance protocols require regular oil level checks and complete oil changes at specified operational intervals using standard heavy-duty motor oil.

The power unit relies exclusively on a forced air-cooling system. Air circulation is generated by a combination fan-flywheel configured with integral blower blades. This airflow is directed over the cylinder block and cylinder head fins via a form-fitted sheet-metal air shroud, which divides and directs the air via ducts and internal baffle plates. The engine must never be operated with any portion of the shrouding removed, as this disrupts the engineered airflow path and causes rapid engine overheating.

General Technical Data

Engine Specifications

Engine Model ............... Wisconsin BKN
Engine Type ............... 4-cycle single-cylinder air-cooled heavy-duty gasoline
Number of Cylinders ............... 1
Cylinder Arrangement ............... Vertical upright single cylinder
Engine Bore, in (mm) ............... 2.87 (73.02)
Engine Stroke, in (mm) ............... 2.75 (69.85)
Displacement, cu.in (cc) ............... 17.8 (291.7)
Gross Power at 1600 rpm, hp (kW) ............... 3.5 (2.6)
Gross Power at 2000 rpm, hp (kW) ............... 4.6 (3.4)
Gross Power at 2400 rpm, hp (kW) ............... 5.6 (4.2)
Gross Power at 3000 rpm, hp (kW) ............... 6.4 (4.8)
Gross Power at 3600 rpm, hp (kW) ............... 7.0 (5.2)
Maximum Speed, rpm ............... 3600
Minimum Speed, rpm ............... 1600
Maximum Torque at 2200 rpm, lb-ft (Nm) ............... 11.2 (15.2)
Idle Speed, rpm ............... 1000-1200
Compression Ratio ............... 5.1:1
Rotation Direction ............... Clockwise from flywheel end
Main Bearings Type ............... Tapered roller bearings on front and rear journals
Valve Layout ............... L-head side-valve side-by-side design
Number of Valves per Cylinder ............... 2
Cylinder Block Material ............... Cast iron integrated crankcase
Cylinder Head Material ............... Cast iron removable head
Piston Material ............... Aluminum alloy split-skirt cam-ground
Muffler Type ............... Low-backpressure exhaust silencer canister
Breather Type ............... Crankcase reed-valve flutter type atmospheric vent
Lubrication System ............... Splash system with positive action oil plunger pump feed
Oil Plunger Pump Drive ............... Camshaft eccentric lobe actuated
Cooling System ............... Forced air-cooled via flywheel blower shroud
Air Cleaner Type (Std) ............... Oil bath type multi-mesh core
Air Cleaner Type (Opt) ............... Dry element pleated paper disposable cartridge
Ignition System ............... High-tension magneto flywheel or battery ignition distributor

Fuel System

Carburetor Manufacturer ............... Zenith or Stromberg Model L26A
Carburetor Type ............... Down-draft or horizontal side-draft balanced venturi float feed
Choke Control Type ............... Manual cable-operated butterfly valve lever assembly
Throttle Control Type ............... Governor-linked speed regulating lever assembly
Fuel Tank Capacity, gal (L) ............... 1.0 (3.785)
Fuel Tank Material ............... Heavy gauge sheet steel terne-plated inside body
Fuel Feed Method ............... Gravity feed or mechanical diaphragm cam-driven fuel pump
Fuel Pump Actuation ............... Camshaft fuel pump eccentric lobe roller arm
Fuel Pump Operating Pressure, psi (kPa) ............... 1.5-2.5 (10.3-17.2)
Governor Type ............... Centrifugal mechanical flyweight internal governor
Fuel Strainer Type ............... Sediment glass bowl with fine mesh brass screen wire element
Fuel Shut-Off Valve ............... Needle valve manual type integrated screen assembly
Main Jet Specification ............... Fixed main jet metering orifice standard high speed
Idle Jet Orifice Diameter, in (mm) ............... 0.018 (0.457)
Idle Air Adjustment Needle ............... Adjustable spring-loaded tapered needle brass screw
Float Setting Height, in (mm) ............... 1.156 (29.367)
Float Needle Valve Seat Orifice, in (mm) ............... 0.062 (1.575)
Recommended Fuel Grade ............... Regular automotive grade gasoline unleaded leaded
Minimum Fuel Octane Rating, RON ............... 90.0
Fuel Lines Material ............... Copper tubing or flexible fuel-resistant reinforced rubber hose
Fuel Lines Outer Diameter, in (mm) ............... 0.250 (6.350)
Governor Linkage Rod Diameter, in (mm) ............... 0.156 (3.962)
Governor Spring Position Holes ............... Multi-hole variable speed adjustment arm bracket

Dimensions and Weight

Overall Height, in (mm) ............... 18.5 (470)
Overall Width, in (mm) ............... 15.2 (385)
Overall Length, in (mm) ............... 14.1 (360)
Dry Weight, lbs (kg) ............... 76 (34.5)
Shipping Weight, lbs (kg) ............... 88 (40)

Maintenance Data

Service Information

Cylinder Compression Pressure, psi (kPa) ............... 100-115 (689-792)
Minimum Acceptable Compression Pressure, psi (kPa) ............... 75 (517)
Ignition Breaker Point Gap, in (mm) ............... 0.015 (0.381)
Distributor Breaker Point Gap, in (mm) ............... 0.020 (0.508)
Spark Plug Gap, in (mm) ............... 0.030 (0.762)
Standard Spark Plug ............... Champion D-16J or AC C86 Commercial
Intake Valve Clearance (Cold), in (mm) ............... 0.008 (0.203)
Exhaust Valve Clearance (Cold), in (mm) ............... 0.014 (0.356)

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) ............... 1.0 (0.95)
Oil Bath Air Cleaner Oil Capacity, pt (L) ............... 0.25 (0.12)
Reduction Gear Box Oil Capacity, pt (L) ............... 0.5 (0.24)

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 Inner Diameter, in (mm) ............... 2.875-2.876 (73.025-73.050)
Cylinder Bore Maximum Out of Round, in (mm) ............... 0.003 (0.076)
Cylinder Bore Maximum Tapered, in (mm) ............... 0.004 (0.102)
Crankshaft Main Journal Outer Diameter, in (mm) ............... 1.3780-1.3785 (35.001-35.014)
Crankshaft Crankpin Journal Diameter, in (mm) ............... 1.3750-1.3755 (34.925-34.938)
Crankshaft End Play Mechanical Allowance, in (mm) ............... 0.001-0.004 (0.025-0.102)
Connecting Rod Big End Bore Inner Diameter, in (mm) ............... 1.3760-1.3765 (34.950-34.963)
Connecting Rod Radial Clearance, in (mm) ............... 0.0005-0.0015 (0.013-0.038)
Connecting Rod Big End Side Clearance, in (mm) ............... 0.004-0.008 (0.102-0.203)
Connecting Rod Small End Bushing Inner Diameter, in (mm) ............... 0.6255-0.6259 (15.888-15.898)
Piston to Cylinder Bore Clearance, in (mm) ............... 0.0035-0.0040 (0.089-0.102)
Piston Pin Bore Inner Diameter, in (mm) ............... 0.6251-0.6254 (15.877-15.885)
Piston Pin Outer 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 Connecting Rod Bushing Clearance, in (mm) ............... 0.0005-0.0011 (0.013-0.028)
Top Ring Groove Width, in (mm) ............... 0.095-0.096 (2.413-2.438)
Second Ring Groove Width, in (mm) ............... 0.095-0.096 (2.413-2.438)
Third Ring Groove Width, in (mm) ............... 0.095-0.096 (2.413-2.438)
Oil Ring Groove Width, in (mm) ............... 0.188-0.189 (4.775-4.801)
Top Ring Side Clearance, in (mm) ............... 0.002-0.004 (0.051-0.102)
Second Ring Side Clearance, in (mm) ............... 0.0015-0.0035 (0.038-0.089)
Third Ring Side Clearance, in (mm) ............... 0.0015-0.0035 (0.038-0.089)
Oil Ring Side Clearance, in (mm) ............... 0.001-0.003 (0.025-0.076)
Top Ring End Gap, in (mm) ............... 0.007-0.015 (0.178-0.381)
Second Ring End Gap, in (mm) ............... 0.007-0.015 (0.178-0.381)
Third Ring End Gap, in (mm) ............... 0.007-0.015 (0.178-0.381)
Oil Ring End Gap, in (mm) ............... 0.007-0.015 (0.178-0.381)
Cylinder Head Flatness Surface, in (mm) ............... 0.003 (0.076)
Intake Valve Head Diameter, in (mm) ............... 1.218 (30.937)
Exhaust Valve Head Diameter, in (mm) ............... 1.125 (28.575)
Intake Valve Stem Outer Diameter, in (mm) ............... 0.310 (7.874)
Exhaust Valve Stem Outer Diameter, in (mm) ............... 0.309 (7.848)
Intake Valve Stem to Guide Clearance, in (mm) ............... 0.0015-0.0035 (0.038-0.089)
Exhaust Valve Stem to Guide Clearance, in (mm) ............... 0.0025-0.0045 (0.063-0.114)
Intake Valve Guide Inner Diameter, in (mm) ............... 0.312 (7.925)
Exhaust Valve Guide Inner Diameter, in (mm) ............... 0.312 (7.925)
Valve Face Angle, deg ............... 45
Valve Seat Angle, deg ............... 45
Valve Spring Free Length, in (mm) ............... 1.625 (41.275)
Camshaft Main Journal Bearing Diameter, in (mm) ............... 0.6245-0.6250 (15.862-15.875)
Camshaft Journal Running Clearance, in (mm) ............... 0.001-0.0025 (0.025-0.063)
Camshaft End Play, in (mm) ............... 0.002-0.006 (0.051-0.152)
Tappet Guide Bore Inner Diameter, in (mm) ............... 0.375-0.376 (9.525-9.550)
Tappet Stem Outer Diameter, in (mm) ............... 0.373-0.374 (9.474-9.500)
Tappet Stem Running Clearance, in (mm) ............... 0.001-0.003 (0.025-0.076)

Tightening Torques

Cylinder Head Bolts, lb-ft (Nm) ............... 22-24 (29.8-32.5)
Connecting Rod Cap Bolts, lb-ft (Nm) ............... 22-28 (29.8-37.9)
Flywheel Retention Nut, lb-ft (Nm) ............... 45-50 (61.0-67.8)
Crankcase Mounting Screws, lb-ft (Nm) ............... 18-22 (24.4-29.8)
Cylinder Block Inspection Plates Screws, lb-ft (Nm) ............... 8-10 (10.8-13.5)
Valve Inspection Cover Nut, lb-ft (Nm) ............... 5-7 (6.8-9.5)
Spark Plug Core, lb-ft (Nm) ............... 24-28 (32.5-37.9)
Magneto Stator Base Plate Mounting Screws, lb-ft (Nm) ............... 6-8 (8.1-10.8)
Governor Housing Lock Screws, lb-ft (Nm) ............... 5-7 (6.8-9.5)
Crankcase Oil Drain Plug, lb-ft (Nm) ............... 20-25 (27.1-33.9)
Oil Plunger Pump Body Screws, lb-ft (Nm) ............... 8-10 (10.8-13.5)
Carburetor to Intake Manifold Nuts, lb-ft (Nm) ............... 10-14 (13.5-19.0)
Intake Manifold to Cylinder Block Bolts, lb-ft (Nm) ............... 14-18 (19.0-24.4)
Exhaust Pipe Nipple Muffler Assembly, lb-ft (Nm) ............... 35-45 (47.4-61.0)
Air Cleaner Mounting Bracket Arm Screws, lb-ft (Nm) ............... 12-15 (16.3-20.3)
Fuel Tank Support Straps Retention Nuts, lb-ft (Nm) ............... 6-9 (8.1-12.2)
Fuel Pump Flange Mounting Screws, lb-ft (Nm) ............... 12-14 (16.3-19.0)
Governor Lever Arm Pinch Bolt, lb-ft (Nm) ............... 7-9 (9.5-12.2)
Breaker Point Terminal Screw, lb-in (Nm) ............... 12-15 (1.35-1.69)
Magneto Coil Core Clamp Screws, lb-ft (Nm) ............... 5-7 (6.8-9.5)
Flywheel Alternator Ring Mounting Screws, lb-ft (Nm) ............... 8-10 (10.8-13.5)
Starter Motor Housing Long Flange Bolts, lb-ft (Nm) ............... 20-24 (27.1-32.5)
Reduction Housing Case Joining Screws, lb-ft (Nm) ............... 22-26 (29.8-35.2)
Clutch Backing Pressure Plate Bolts, lb-ft (Nm) ............... 16-20 (21.7-27.1)
Crankshaft Extension Output Drive Set Screw, lb-ft (Nm) ............... 12-15 (16.3-20.3)
Air Shroud Shield Deflector Fasteners, lb-in (Nm) ............... 35-45 (3.95-5.08)
Oil Plunger Screen Frame Base Nut, lb-ft (Nm) ............... 14-18 (19.0-24.4)
Tappet Adjusting Screw Jam Nut, lb-ft (Nm) ............... 10-12 (13.5-16.3)

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

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