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Wisconsin S10D Engine

The Wisconsin S10D is a heavy-duty, industrial-grade, single-cylinder Wisconsin Air-Cooled Engine. Designed for agricultural, construction, and stationary utility platforms, this engine utilizes a rugged cast-iron crankcase and cylinder structure. Operating on a four-stroke internal combustion cycle, it delivers high torque at lower operational ranges. Modernized iterations starting from serial number 4225490 incorporate an automatic mechanical compression release mechanism directly inside the camshaft assembly to significantly minimize recoil force during manual rope or electric starting sequences.

Valve Configuration: The engine utilizes a side-valve (L-head) layout built into the cylinder block assembly. It features one intake valve and one exhaust valve per cylinder, paired with heavy-duty valve springs, stem guides, and hardened valve seat inserts. The exhaust assembly is equipped with an integrated mechanical rotator to promote even thermal distribution across the valve face. Bore and Stroke: Internal cylinder geometry consists of a fixed 3-1/4 inch bore matched to a 3 inch stroke. This internal configuration yields a total displacement profile of exactly 24.89 cubic inches.

Fuel System: Air-fuel delivery is managed by a balanced float-feed carburetor, typically utilizing a genuine Zenith Carburetor Unit or an alternate Walbro design. Fuel delivery is pulled from a frame-mounted or side-mounted gravity tank configuration through a sequence containing a dedicated fuel shut-off valve and an inline sediment strainer. Combustion mixtures pass directly through a regulated governor throttle linkage to optimize fuel-to-air ratios dynamically across all variable load thresholds.

Lubrication: Internal component protection uses a reliable splash lubrication system. A dedicated oil dipper, structurally secured to the bottom cap of the connecting rod assembly, repeatedly strikes the oil reservoir in the lower crankcase basin during crankshaft rotations. This dynamic motion converts the standing fluid into a highly dispersed oil spray and mist, covering the interior cylinder walls, wrist pins, and critical main bearings.

Cooling: Thermal regulation is handled through a high-velocity forced air-cooling assembly. A unified combination fan-flywheel unit draws in surrounding air and pushes it directly into a surrounding stamped sheet-metal shroud. Internal air shrouding, structural ducts, and custom deflector plates isolate the airflow, routing it tightly over the external cooling fins of the cylinder block and cylinder head to maintain uniform operational temperatures.

General Technical Data

Engine Specifications

Engine Model ............... Wisconsin S10D
Engine Type ............... 4-cycle single-cylinder air-cooled gasoline
Number of Cylinders ............... 1
Engine Bore, in (mm) ............... 3.25 (82.5)
Engine Stroke, in (mm) ............... 3.00 (76.2)
Displacement, cu.in (cc) ............... 24.89 (407.8)
Rated Power, hp (kW) ............... 10.5 (7.8) at 3600 rpm
Maximum Power, hp (kW) ............... 10.5 (7.8) at 3600 rpm
Continuous Power, hp (kW) ............... 8.4 (6.3) at 3600 rpm
Rated Speed, rpm ............... 1600-3600
Peak Torque, lb-ft (Nm) ............... 18.2 (24.7) at 2400 rpm
Low Idle Speed, rpm ............... 1000-1200
High Idle Speed, rpm ............... 3800-3900
Compression Ratio ............... 6.5:1
Rotation Direction ............... Counter-clockwise facing power take off shaft side
Valves per Cylinder ............... 2 (1 intake, 1 exhaust)
Valve Configuration ............... L-head side valve flathead architecture
Exhaust Valve Rotator ............... Optional stellite mechanical rotators
Crankshaft Type ............... Forged steel counterweighted heat treated
Main Bearings Type ............... Tapered roller bearings dual outer layout
Connecting Rod Material ............... Forged aluminum alloy or forged steel option
Camshaft Type ............... Cast iron with hardened lobes gear driven
Cylinder Block Material ............... Cast iron
Cylinder Head Material ............... Cast iron aluminum alloy option
Crankcase Material ............... Cast iron heavy duty
Flywheel Material ............... Cast iron balanced
Lubrication System ............... Splash lubrication with oil plate
Oil Pump Type ............... Mechanical splash flinger dipper
Oil Filtration Type ............... Optional screen strainer mesh
Cooling System ............... Air-cooled forced heavy duty
Cooling Fan Type ............... Flywheel integrated blower shroud
Air Cleaner Type ............... Polyurethane foam element or oil bath
Ignition System Type ............... Solid state breakerless magneto or flywheel magneto
Starting System ............... Rope start or optional electric starter motor
Electrical System ............... 12V DC options

Fuel System

Carburetor Type ............... Zenith or Walbro side-draft float feed type
Choke Type ............... Manual cable operated lever butterfly valves
Fuel Delivery Type ............... Gravity feed standard or mechanical diaphragm pump
Governor Type ............... Centrifugal flyweight mechanical governor
Fuel Tank Capacity, Standard, gal (L) ............... 1.50 (5.68)
Fuel Tank Capacity, Optional, gal (L) ............... 2.25 (8.52)
Fuel Recommended Grade ............... Regular unleaded automotive gasoline
Minimum Octane Rating, AKI (RON) ............... 87 (90)
Fuel Strainer Type ............... Sediment bowl with fine mesh screen insert
Main Jet Size Identification ............... Fixed orifice standard adjustable options
Idle Jet Size Identification ............... Adjustable needle valve air screw setting
Float Setting Clearance, in (mm) ............... 0.234 (5.94) to float chamber gasket surface
Venturi Diameter, in (mm) ............... 0.750 (19.05) optimized bore internal diameter
Fuel Line Material ............... Steel tube copper plated or flexible rubber
Fuel Line Outer Diameter, in (mm) ............... 0.250 (6.35)
Fuel Consumption Rated, gal/hr (L/hr) ............... 0.95 (3.60)
Fuel Consumption Half Load, gal/hr (L/hr) ............... 0.55 (2.08)
Governor Spring Tension Fuel Linkage ............... Mechanical adjustable tension anchor holes

Dimensions and Weight

Overall Length, in (mm) ............... 14.875 (377.83)
Overall Width, in (mm) ............... 16.250 (412.75)
Overall Height, in (mm) ............... 18.500 (469.90)
Dry Weight, lbs (kg) ............... 88.00 (39.92)
Shipping Weight, lbs (kg) ............... 104.00 (47.17)

Maintenance Data

Service Information

Cylinder Compression Pressure, psi (kPa) ............... 90.00 (620.53)
Spark Plug Gap, in (mm) ............... 0.030 (0.76)
Breaker Point Gap, in (mm) ............... 0.020 (0.51)
Armature Air Gap, in (mm) ............... 0.012 (0.30) to 0.015 (0.38)
Ignition Timing, deg ............... 20.0 deg BTDC
Intake Valve Clearance, in (mm) ............... 0.0080 (0.203)
Exhaust Valve Clearance, in (mm) ............... 0.0160 (0.406)

Engine Oil

Engine Oil Type .................. SAE 30, SAE 20W, or SAE 10W
API Service Classifications ......................... MS, SD, SE, or SF
Crankcase Oil Capacity, qt (L) ............... 1.25 (1.18)
Reduction Gearbox Oil Capacity, pt (L) ............... 0.50 (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 100 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
Change reduction gear oil ............... Every 500 hours

Service Specifications

Cylinder Bore Inside Standard, in (mm) ............... 3.2500 (82.550) to 3.2510 (82.575)
Cylinder Out of Round Maximum, in (mm) ............... 0.0020 (0.051)
Cylinder Taper Maximum, in (mm) ............... 0.0025 (0.064)
Connecting Rod Big End Journal Diameter, in (mm) ............... 1.6250 (41.275) to 1.6255 (41.288)
Connecting Rod Oil Clearance, in (mm) ............... 0.0013 (0.033) to 0.0028 (0.071)
Connecting Rod Axial Side Play, in (mm) ............... 0.0060 (0.152) to 0.0120 (0.305)
Crankshaft Main Journal Diameter, in (mm) ............... 1.7500 (44.450) to 1.7505 (44.463)
Crankshaft Main Bearing Bore Housing, in (mm) ............... 2.4410 (62.001) to 2.4415 (62.014)
Crankshaft End Play, in (mm) ............... 0.002 (0.05) to 0.005 (0.13)
Piston to Cylinder Bore Clearance, in (mm) ............... 0.0035 (0.089) to 0.0045 (0.114)
Piston Pin Diameter, in (mm) ............... 0.7500 (19.050) to 0.7503 (19.058)
Piston Pin to Piston Pin Bore Clearance, in (mm) ............... 0.0000 (0.000) to 0.0003 (0.008)
Piston Pin Bushing Inner Diameter, in (mm) ............... 0.7505 (19.063) to 0.7510 (19.075)
Top Ring Groove Clearance, in (mm) ............... 0.0020 (0.051) to 0.0040 (0.102)
Second Ring Groove Clearance, in (mm) ............... 0.0015 (0.038) to 0.0035 (0.089)
Oil Ring Groove Clearance, in (mm) ............... 0.0010 (0.025) to 0.0030 (0.076)
Top Ring End Gap, in (mm) ............... 0.0100 (0.254) to 0.0200 (0.508)
Second Ring End Gap, in (mm) ............... 0.0080 (0.203) to 0.0180 (0.457)
Oil Ring End Gap, in (mm) ............... 0.0080 (0.203) to 0.0180 (0.457)
Intake Valve Port Diameter, in (mm) ............... 1.250 (31.75)
Exhaust Valve Port Diameter, in (mm) ............... 1.125 (28.58)
Intake Valve Stem Outer Diameter, in (mm) ............... 0.3110 (7.899) to 0.3120 (7.925)
Exhaust Valve Stem Outer Diameter, in (mm) ............... 0.3095 (7.861) to 0.3105 (7.887)
Valve Guide Inner Diameter, in (mm) ............... 0.3135 (7.963) to 0.3145 (7.988)
Intake Valve Stem to Guide Clearance, in (mm) ............... 0.0015 (0.038) to 0.0035 (0.089)
Exhaust Valve Stem to Guide Clearance, in (mm) ............... 0.0030 (0.076) to 0.0050 (0.127)
Valve Seat Angle, deg ............... 45
Valve Face Angle, deg ............... 45
Valve Seat Width, in (mm) ............... 0.0450 (1.143) to 0.0650 (1.651)
Valve Spring Free Length, in (mm) ............... 1.6250 (41.275)
Camshaft Journal Diameter (Front), in (mm) ............... 1.1250 (28.575) to 1.1255 (28.588)
Camshaft Journal Diameter (Rear), in (mm) ............... 0.8750 (22.225) to 0.8755 (22.238)
Camshaft Radial Clearance, in (mm) ............... 0.0015 (0.038) to 0.0035 (0.089)
Cam Lobe Height (Intake), in (mm) ............... 1.4350 (36.449)
Cam Lobe Height (Exhaust), in (mm) ............... 1.4350 (36.449)

Tightening Torques

Cylinder Head Bolts, lb-ft (Nm) ............... 22.00 (29.83)
Connecting Rod Cap Bolts, lb-ft (Nm) ............... 18.00 (24.40)
Flywheel Retention Center Nut, lb-ft (Nm) ............... 70.00 (94.91)
Crankcase Bottom Cover Pan Screws, lb-ft (Nm) ............... 14.00 (18.98)
Gear Cover Main Plate Fasteners, lb-ft (Nm) ............... 14.00 (18.98)
Spark Plug Base Seat Installation, lb-ft (Nm) ............... 26.00 (35.25)
Magneto Stator Frame Mounting Bolts, lb-ft (Nm) ............... 8.00 (10.85)
Governor Housing Assembly Nuts, lb-ft (Nm) ............... 12.00 (16.27)
Intake Exhaust Manifold Screws, lb-ft (Nm) ............... 16.00 (21.69)
Air Shroud Shield Screws, lb-ft (Nm) ............... 6.00 (8.13)
Crankcase Oil Drain Plug, lb-ft (Nm) ............... 20.00 (27.12)
Fuel Tank Support Mounting Fasteners, lb-ft (Nm) ............... 15.00 (20.34)
Valve Cover Access Breather Plate Nut, lb-ft (Nm) ............... 7.00 (9.49)
Starter Motor Housing Bolts, lb-ft (Nm) ............... 24.00 (32.54)

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• Wisconsin Engines Specs
  
• Wisconsin S7D Specs
  
• Wisconsin S8D Specs
  
• Wisconsin S12D Specs
  
• Wisconsin S14D Specs
  

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