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Wisconsin S7D Engine

The Wisconsin S-7D is a heavy-duty, single-cylinder, four-stroke, air-cooled internal combustion engine engineered by the Wisconsin Motor Corporation. Renowned for its cast-iron construction and exceptionally robust, near-indestructible design, this utility powerplant was widely utilized during the mid-to-late 20th century to drive vintage garden tractors, agricultural sprayers, and specialized industrial equipment. The engine is designed to operate reliably under continuous high-load conditions and features a rebuildable architecture with service-accessible clearances.

Valve Configuration: Side-valve layout (commonly designated as an L-head or flathead configuration). Mechanism: Poppet-style intake and exhaust valves driven directly by mechanical gear-driven camshaft tappets located inside the crankcase block. Valve guides and seat inserts are fully serviceable and ground to manual specification. Cylinder Bore: 3.00 inches. Piston Stroke: 2.50 inches (2-5/8 inches). Total Displacement: 18.6 cubic inches.

Lubrication System: Positive splash lubrication system. Operation: A dedicated oil dipper (splash finger) attached directly to the connecting rod cap screw dips into the oil reservoir at the base of the oil pan. This component atomizes the engine oil, generating an internal oil mist that coats the crankshaft journals, camshaft gears, piston wrist pins, and cylinder walls during operation. Cooling System: Forced air-cooled system. Components: A high-velocity flywheel blower fan integrated with a stamped sheet metal wrapper shroud. The shroud captures airflow from the rotating flywheel blades and routes it continuously across the cast-iron cylinder block and cylinder head cooling fins to dissipate thermal energy.

Fuel System: Updraft or side-draft atmospheric carburetion loop utilizing a Zenith or service-replaceable Walbro carburetor. Delivery and Regulation: Fuel delivery occurs via gravity feed or an external mechanical diaphragm fuel pump connected to a heavy-duty fuel tank. Air filtration is handled through a heavy-duty oil-bath or dry element air cleaner assembly. A mechanical flyweight engine governor regulates the carburetor throttle shaft via external spring-loaded linkage rods to automatically match engine load demand and prevent over-speeding.

General Technical Data

Engine Specifications

Engine Model ............... Wisconsin S7D
Engine Type ............... 4-cycle heavy-duty air-cooled single-cylinder L-head gasoline
Number of Cylinders ............... 1
Engine Bore, in (mm) ............... 3.00 (76.2)
Engine Stroke, in (mm) ............... 2.625 (66.68)
Displacement, cu.in (cc) ............... 18.6 (305.0)
Rated Engine Power, hp (kW) ............... 7.25 (5.4) at 3600 rpm
Minimum Power Output, hp (kW) ............... 3.80 (2.8) at 1600 rpm
Intermediate Power Output, hp (kW) ............... 5.60 (4.2) at 2400 rpm
High-Speed Power Output, hp (kW) ............... 6.60 (4.9) at 3000 rpm
Rated Engine Speed, rpm ............... 1600-3600
Maximum Governor Speed, rpm ............... 3800
Idle Speed, rpm ............... 1000-1200
Peak Torque, lb-ft (Nm) ............... 11.2 (15.2) at 2400 rpm
Compression Ratio ............... 6.2:1
Rotation Direction ............... Counter-clockwise facing power take-off shaft end
Valve Location ............... Side valve L-head placement engine block integrated
Camshaft Drive Mechanism ............... Gear-driven helical gear arrangement
Muffler Configuration ............... Side exhaust standard canister industrial grade
Crankshaft Type ............... Counterbalanced ductile iron or forged steel alloy
Main Bearing Type ............... Heavy-duty tapered roller bearings on double ends
Connecting Rod Material ............... High-tensile aluminum alloy construction
Piston Material ............... Aluminum alloy cam ground design
Cylinder Block Material ............... Cast iron
Cylinder Head Material ............... Cast iron
Crankcase Material ............... Cast iron
Lubrication System ............... Splash lubrication with oil plate mechanism
Oil Pump Type ............... Non-driven positive splash slinger dipper mechanism
Oil Filtration Type ............... Optional auxiliary oil filter splash screen mesh
Cooling System ............... Heavy-duty forced air cooling via flywheel fan shroud
Air Cleaner Config ............... Oil bath type or dry polyurethane element type
Ignition System ............... Flywheel magneto ignition assembly standard
Magneto Model ............... Wico W7700 or Fairbanks Morse variant
Starting System ............... Rope start standard or electric starter generator motor optional
Electrical System ............... 12V DC standard electric optional kit

Fuel System

Carburetor Manufacturer ............... Zenith Model 687 or Walbro L-104-S1 variant
Carburetor Type ............... Single-barrel downdraft internal float type venturi configuration
Choke Mechanism Control ............... Manual cable-operated choke linkage lever assembly
Throttle Linkage Interface ............... Mechanical governor compensated spring throttle control system
Fuel Delivery Method ............... Gravity feed standard or mechanical fuel pump optional kit
Mechanical Fuel Pump Type ............... Diaphragm-driven mechanical lever off camshaft
Recommended Fuel Grade ............... Regular unleaded gasoline octane level 86 or higher
Fuel Tank Capacity, gal (L) ............... 1.25 (4.73)
Governor System ............... Flyweight mechanical centrifugal governor enclosed assembly
Fuel Line Internal Diameter, in (mm) ............... 0.25 (6.35)
Fuel Line Composition ............... Copper tubing or braided flexible fuel grade rubber hose
Fuel Filter Screen Type ............... Sediment bowl fuel strainer with fine wire mesh screen filter
Main Jet Specification ............... Fixed orifice standard high-speed jet or adjustable needle variant
Idle Speed Mixture Screw Adjustment ............... 1.25 to 1.50 turns open from seat position
High Speed Needle Screw Adjustment ............... 1.50 to 1.75 turns open from closed seat position
Float Setting Level Height, in (mm) ............... 1.53 (38.89)
Venturi Internal Diameter Size, in (mm) ............... 0.75 (19.05)
Fuel Consumption Rate at 2400 rpm, gph (L/h) ............... 0.45 (1.70)
Fuel Consumption Rate at 3000 rpm, gph (L/h) ............... 0.58 (2.20)
Fuel Consumption Rate at 3600 rpm, gph (L/h) ............... 0.72 (2.72)
Fuel Tank Drain Device Type ............... Threaded drain plug bottom tank position port

Dimensions and Weight

Overall Height, in (mm) ............... 16.1 (410)
Overall Width, in (mm) ............... 14.5 (370)
Overall Length, in (mm) ............... 13.7 (350)
Dry Weight, lbs (kg) ............... 76 (34.5)
Shipping Weight, lbs (kg) ............... 88 (40)

Maintenance Data

Service Information

Cylinder Compression, Minimum, psi (bar) ............... 75.0 (5.17)
Spark Plug Type ............... Champion D16 or equivalent
Spark Plug Gap, in (mm) ............... 0.030 (0.762)
Breaker Point Gap (Magneto), in (mm) ............... 0.015 (0.381)
Breaker Point Gap (Distributor), in (mm) ............... 0.020 (0.508)
Ignition Timing ............... 21.0 deg BTDC
Inlet Valve Clearance, Cold, in (mm) ............... 0.006 (0.152)
Exhaust Valve Clearance, Cold, in (mm) ............... 0.012 (0.305)

Engine Oil

Engine Oil Type .................. SAE 30, SAE 10W-30, or SAE 5W-30
API Service Classifications ......................... SE, SF, SG, or CC
Crankcase Oil Capacity Base, qt (L) ............... 1.00 (0.95)
Oil Bath Air Cleaner Sump Capacity, pt (L) ............... 0.25 (0.12)

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 250 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

Service Specifications

Cylinder Bore Inside Diameter, in (mm) ............... 3.0000-3.0005 (76.200-76.213)
Cylinder Bore Maximum Wear Limit, in (mm) ............... 3.0050 (76.327)
Cylinder Bore Out of Round Maximum, in (mm) ............... 0.0020 (0.0508)
Crankshaft Main Journal Diameter, in (mm) ............... 1.6250-1.6255 (41.275-41.288)
Crankshaft Crankpin Journal Diameter, in (mm) ............... 1.3750-1.3755 (34.925-34.938)
Connecting Rod Big End Bearing Clearance, in (mm) ............... 0.0008-0.0020 (0.0203-0.0508)
Connecting Rod Side Play, in (mm) ............... 0.0040-0.0080 (0.1016-0.2032)
Crankshaft End Play, in (mm) ............... 0.0010-0.0040 (0.0254-0.1016)
Piston-to-Cylinder Wall Clearance, in (mm) ............... 0.0040-0.0045 (0.1016-0.1143)
Piston Pin Diameter, in (mm) ............... 0.7500-0.7503 (19.050-19.058)
Piston Pin-to-Piston Pin Bore Clearance, in (mm) ............... 0.0000-0.0008 (0.0000-0.0203)
Piston Pin-to-Con Rod Bushing Clearance, in (mm) ............... 0.0005-0.0010 (0.0127-0.0254)
Top Ring Groove Side Clearance, in (mm) ............... 0.0020-0.0035 (0.0508-0.0889)
Second Ring Groove Side Clearance, in (mm) ............... 0.0015-0.0030 (0.0381-0.0762)
Oil Ring Groove Side Clearance, in (mm) ............... 0.0015-0.0030 (0.0381-0.0762)
Top Ring End Gap, in (mm) ............... 0.0070-0.0150 (0.1778-0.3810)
Second Ring End Gap, in (mm) ............... 0.0070-0.0150 (0.1778-0.3810)
Oil Ring End Gap, in (mm) ............... 0.0070-0.0150 (0.1778-0.3810)
Camshaft Journal Diameter, in (mm) ............... 0.6250-0.6255 (15.875-15.888)
Inlet Valve Stem Outer Diameter, in (mm) ............... 0.3100-0.3110 (7.874-7.899)
Exhaust Valve Stem Outer Diameter, in (mm) ............... 0.3090-0.3100 (7.849-7.874)
Valve Guide Inside Diameter, in (mm) ............... 0.3120-0.3130 (7.925-7.950)
Inlet Valve Stem-to-Guide Clearance, in (mm) ............... 0.0020-0.0040 (0.0508-0.1016)
ExhaustValve Stem-to-Guide Clearance, in (mm) ............... 0.0020-0.0040 (0.0508-0.1016)
Valve Face Angle ............... 45.0 degrees
Valve Seat Angle ............... 45.0 degrees
Valve Seat Contact Width, in (mm) ............... 0.0468-0.0625 (1.189-1.588)
Valve Spring Free Length, in (mm) ............... 1.6875 (42.863)

Tightening Torques

Cylinder Head Stud Hex Nuts Fasteners, lb-ft (Nm) ............... 22.0-24.0 (29.8-32.5)
Connecting Rod Cap Locking Cap Screws, lb-ft (Nm) ............... 14.0-16.0 (19.0-21.7)
Flywheel Center Shaft Retaining Nut Sizer, lb-ft (Nm) ............... 55.0-60.0 (74.6-81.3)
Crankcase Cover Flange Mount Fasteners, lb-ft (Nm) ............... 10.0-12.0 (13.6-16.3)
Spark Plug Core Shell Mechanical Seating, lb-ft (Nm) ............... 24.0-28.0 (32.5-37.9)
Magneto Stator Frame Mounting Plate Screws, lb-in (Nm) ............... 35.0-45.0 (3.95-5.08)
Camshaft Thrust Flange Retaining Cap Screws, lb-in (Nm) ............... 70.0-80.0 (7.91-9.04)
Governor Lever Arm Pinch Bolt Clamp Fastener, lb-in (Nm) ............... 45.0-55.0 (5.08-6.21)
Fuel Tank Support Mounting Bracket Fasteners, lb-ft (Nm) ............... 12.0-14.0 (16.3-19.0)
Exhaust Pipe Manifold Hex Nut Fasteners, lb-ft (Nm) ............... 14.0-16.0 (19.0-21.7)
Carburetor Air Horn Intake Mounting Studs, lb-in (Nm) ............... 55.0-65.0 (6.21-7.34)
Oil Sump Drain Plug External Pipe Thread, lb-ft (Nm) ............... 18.0-22.0 (24.4-29.8)
Air Shroud Shield Tin Enclosure Fasteners, lb-in (Nm) ............... 25.0-35.0 (2.82-3.95)
Breather Plate Cover Housing Cap Screws, lb-in (Nm) ............... 35.0-45.0 (3.95-5.08)
Valve Inspection Chamber Cover Hex Nuts, lb-in (Nm) ............... 40.0-50.0 (4.52-5.65)
Starter Generator Pivot Mount Hinge Bolt, lb-ft (Nm) ............... 20.0-25.0 (27.1-33.9)
Starter Generator Adjusting Brace Arm Bolt, lb-ft (Nm) ............... 12.0-15.0 (16.3-20.3)
Flywheel Air Shroud Backing Plate Fasteners, lb-in (Nm) ............... 60.0-75.0 (6.78-8.47)
Intermittent Fuel Pump Mount Cover Bolts, lb-in (Nm) ............... 65.0-75.0 (7.34-8.47)
Governor Weight Assembly Retaining Nut Shaft, lb-ft (Nm) ............... 15.0-18.0 (20.3-24.4)
Crankcase Base Anchorage Equipment Bolts, lb-ft (Nm) ............... 25.0-30.0 (33.9-40.7)

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• Wisconsin Engines Specs
  
• Wisconsin S8D Specs
  
• Wisconsin S10D Specs
  
• Wisconsin S12D Specs
  
• Wisconsin S14D Specs
  

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