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Wisconsin S8D Engine

The Wisconsin S-8D is a heavy-duty, industrial-grade, single-cylinder, four-stroke internal combustion engine. Engineered for high-endurance applications like garden tractors, pumps, and agricultural machinery, it features a cast-iron cylinder block and crankcase assembly to withstand severe operating environments. The "D" designation specifies the integration of stellite-faced exhaust valves and solid stellite inserts to tolerate extreme thermal stress. This air-cooled, horizontal-shaft engine is configured for maximum structural rigidity and field reliability under continuous load profiles.

The powerhead utilizes an L-head (side-valve or "flathead") configuration where the intake and exhaust valves operate parallel to the cylinder bore within the block casting. Valves are actuated via mechanical flat tappets interacting directly with the camshaft. The exhaust circuit utilizes premium stellite-coated faces and seats to increase resistance to heat scaling and high-temperature wear. Mechanical valve lash adjustments must be manually configured at the tappets via the valve inspection chamber. Cylinder Bore: 3.125 in (79.37 mm). Piston Stroke: 2.625 in (66.67 mm). Total Displacement: 20.2 cu.in (331 cc).

The fuel induction system consists of an external fuel reservoir providing fuel via gravity or a mechanical fuel pump assembly to a side-mounted carburetor unit. Engine models alternate fuel mixers depending on production serial numbers: early configurations carry a Zenith assembly, while engines beginning with serial number 5558441 feature a Walbro LME-73 / L-104-S1 updraft carburetor. Combustion air passes through a heavy-duty side-mount air cleaner containing a reusable filter element to trap dust particles before the air-fuel mixture passes into the intake manifold.

Lubrication is managed through a self-contained internal splash system combined with a mechanical oil pump assembly. The internal pump forces oil to critical stress headers, while matching connecting rod oil channels feed the crankpin bearings. Excess oil is discharged through internal spray nozzles, creating a consistent pressurized oil mist that saturates the cylinder walls, camshaft lobes, governor mechanism, and timing gear train. Sump levels must be checked every 8 hours, requiring complete oil replacement after scheduled operating intervals to clear suspended metallic friction particulates.

Thermal regulation is completely air-cooled via a high-velocity forced-air configuration. A combination fan-flywheel draws air through the intake shroud. This air is then split, pressurized, and forcefully directed across the cylinder block and cylinder head fins via a system of precisely contoured sheet metal ducts and air shrouding baffles. Operation of the power unit without all factory air shrouds securely fastened is strictly prohibited due to instantaneous localized overheating risks.

General Technical Data

Engine Specifications

Engine Model ............... Wisconsin S-8D
Engine Type ............... 4-cycle single cylinder air-cooled horizontal-shaft gasoline
Number of Cylinders ............... 1
Engine Bore, in (mm) ............... 3.125 (79.37)
Engine Stroke, in (mm) ............... 2.625 (66.67)
Displacement, cu.in (cc) ............... 20.2 (331.0)
Rated Engine Power, hp (kW) ............... 8.25 (6.2) at 3600 rpm
Rated Engine Speed, rpm ............... 1600-3600
Peak Torque ............... 14.3 Nm (10.55 lb-ft) at 2400 rpm
Idle Speed ............... 1000-1200 rpm
Operating Speed ............... 3600 rpm
Compression Ratio ............... 6.5:1
Cylinder Block Type ............... Cast iron
Cylinder Head Type ............... Cast iron aluminum alloy optional
Lubrication System ............... Splash lubrication with oil pump dipper
Oil Pump Type ............... Plunger-driven cam-actuated
Oil Filter Type ............... Internal screen element mesh
Cooling System ............... Air-cooled forced fly-wheel blower housing vanes
Air Cleaner Type ............... Oil bath or dry paper element polyurethane pre-cleaner
Ignition System ............... Flywheel magneto unit or battery conversion distributor
Starting System ............... Electric Starter Generator or Recoil Rope Starter
Electrical System ............... 12V flywheel magneto alternator combination system

Fuel System

Carburetor Manufacturer ............... Zenith or Walbro
Carburetor Model Variant ............... Zenith 72Y6 L-80 series or Walbro L-104-S1
Choke Control Mechanism ............... Manual lever cable operated remote option
Main Jet Configuration ............... Adjustable needle jet assembly or fixed jet variant
Idle Jet Configuration ............... Adjustable idle mixture air needle screw
Float Height Setting, in (mm) ............... 0.6875 (17.46)
Initial Main Jet Setting ............... 2.0 full turns open from seat position
Initial Idle Jet Setting ............... 1.25 full turns open from seat position
Fuel Pump Type ............... Diaphragm driven by auxiliary camshaft lobe crankcase element
Fuel Tank Volume Capacity, gal (L) ............... 1.0 (3.78)
Fuel Grade Minimum Recommendation ............... 87 Octane unleaded regular gasoline
Governor System ............... Mechanical flyweight centrifugal governor design linkage system
Fuel Filter Screen Design ............... Fuel tank internal sediment bowl screen strainer

Dimensions and Weight

Overall Height, in (mm) ............... 14.5 (370)
Overall Width, in (mm) ............... 13.7 (350)
Overall Length, in (mm) ............... 12.2 (310)
Dry Weight, lbs (kg) ............... 82 (37.19)

Maintenance Data

Service Information

Compression Pressure Test, psi (kPa) ............... 100.0-115.0 (689.4-792.8)
Spark Plug Model ............... Champion D-16J or equivalent
Spark Plug Gap, in (mm) ............... 0.030 (0.76)
Breaker Point Gap, in (mm) ............... 0.020 (0.51)
Ignition Timing ............... 18.0 degrees
Intake Valve Clearance (Cold), in (mm) ............... 0.006 (0.15)
Exhaust Valve Clearance (Cold), in (mm) ............... 0.012 (0.30)

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) ............... 3.1250-3.1255 (79.375-79.387)
Cylinder Bore Max Taper Out-of-Round, in (mm) ............... 0.003 (0.076)
Connecting Rod Journal Diameter, in (mm) ............... 1.375 (34.92)
Connecting Rod to Crankpin Clearance, in (mm) ............... 0.0007-0.0020 (0.017-0.051)
Connecting Rod Side Clearance, in (mm) ............... 0.004-0.010 (0.101-0.254)
Main Bearing Journal Outer Diameter, in (mm) ............... 1.3752-1.3757 (34.930-34.942)
Crankshaft End Play, in (mm) ............... 0.001-0.004 (0.025-0.101)
Piston to Cylinder Bore Clearance, in (mm) ............... 0.0025-0.0040 (0.063-0.101)
Piston Pin Bore Inside Diameter, in (mm) ............... 0.6875-0.6878 (17.462-17.470)
Piston Pin to Con Rod Small End Clearance, in (mm) ............... 0.0005-0.0011 (0.012-0.027)
Top Ring Groove Side Clearance, in (mm) ............... 0.002-0.0035 (0.051-0.089)
Second Ring Groove Side Clearance, in (mm) ............... 0.002-0.0035 (0.051-0.089)
Oil Ring Groove Side Clearance, in (mm) ............... 0.001-0.0025 (0.025-0.063)
Top Ring End Gap, in (mm) ............... 0.007-0.017 (0.177-0.431)
Second Ring End Gap, in (mm) ............... 0.007-0.017 (0.177-0.431)
Oil Ring End Gap, in (mm) ............... 0.007-0.017 (0.177-0.431)
Intake Valve Stem to Guide Clearance, in (mm) ............... 0.0015-0.0035 (0.038-0.088)
Exhaust Valve Stem to Guide Clearance, in (mm) ............... 0.0030-0.0050 (0.076-0.127)
Valve Guide Installed Depth Height , in (mm) ............... 1.062 (26.97)
Valve Face Angle, Degrees ............... 45.0
Valve Seat Width, in (mm) ............... 0.046-0.062 (1.16-1.57)
Valve Spring Free Length, in (mm) ............... 1.562 (39.67)
Camshaft Journal Bearing Diameter, in (mm) ............... 0.500-0.501 (12.70-12.72)
Camshaft Journal Clearance, in (mm) ............... 0.001-0.0025 (0.025-0.063)

Tightening Torques

Cylinder Head Stud Nuts ............... 22-24 ft-lbs (30-32 Nm)
Connecting Rod Cap Screws ............... 22-24 ft-lbs (30-32 Nm)
Crankcase Cover Main Outer Bolts ............... 20-22 ft-lbs (27-30 Nm)
Flywheel Output Mounting Nut ............... 50-55 ft-lbs (68-74 Nm)
Spark Plug Base ............... 28-30 ft-lbs (38-41 Nm)
Breaker Points Stationary Assembly Screw ............... 15-20 in-lbs (1.7-2.2 Nm)
Governor Lever Pinch Clamp Assembly Bolt ............... 45-50 in-lbs (5.1-5.6 Nm)
Oil Sump Drain Plug ............... 15-18 ft-lbs (20-24 Nm)
Manifold Exhaust Intake Union Flange Studs ............... 18-20 ft-lbs (24-27 Nm)
Fuel Pump Flange Mounting Crankcase Bolts ............... 12-14 ft-lbs (16-19 Nm)
Stator Core Plate Attachment Screw Units ............... 14-16 ft-lbs (19-22 Nm)
Starter Generator Support Pivot Mounting Bolts ............... 25-28 ft-lbs (34-38 Nm)
Muffler Deflector Thread Coupling Pipe Body ............... 35-40 ft-lbs (47-54 Nm)
Rope Sheave Cup Pulley Starter Screws ............... 8-10 ft-lbs (11-14 Nm)
Air Cleaner Mounting Bracket Nut ............... 45-55 in-lbs (5.1-6.2 Nm)
Valve Cover Breather Shield Assembly Screw ............... 35-45 in-lbs (3.9-5.1 Nm)
Oil Pump Base Crankcase Cap Screw ............... 10-12 ft-lbs (14-16 Nm)
Crankshaft Bearing Plate Flange Bolts ............... 16-18 ft-lbs (22-24 Nm)
Flywheel Housing Air Shroud Screws ............... 6-8 ft-lbs (8-11 Nm)

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• Wisconsin Engines Specs
  
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• Wisconsin S12D Specs
  
• Wisconsin S14D Specs
  

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