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Tecumseh OH120 Engine

General Technical Data

Tecumseh OH120 Engine Specifications

Engine Model ........... Tecumseh OH120
Engine Type ........... 4-cycle single-cylinder overhead valve horizontal air-cooled gasoline engine
Number of Cylinders ........... 1
Displacement, cu.in (cc) ........... 21.1 (346)
Cylinder Bore, in (mm) ........... 3.13 (79.3)
Piston Stroke, in (mm) ........... 2.75 (69.9)
Rated Engine Power, hp (kW) ........... 12.0 (8.6)
Rated Engine Speed, rpm ........... 3600
Maximum Torque, Nm (ft-lbs) ........... 25.1 (18.5)
Torque Speed, rpm ........... 2800
Compression Ratio ........... 8.6:1
Lubrication System ........... Splash type
Air Cleaner ........... Paper element
Cooling System ........... Forced air
Ignition System ........... Solid state magneto
Starting System ........... Recoil or electric starter
Crankshaft ........... Iron alloy
Cylinder ........... Cast iron alloy
Electrical System Rating, Volts ........... 12

Fuel System

Fuel System Type ........... Carburetor
Carburetor Type ........... Float, adjustable jet
Governor Type ........... Mechanical

Dimensions and Weight

Overall Length, in (mm) ........... 18.5 (468)
Overall Width, in (mm) ........... 13.2 (334)
Overall Height, in (mm) ........... 18.5 (468)
Net Weight, lbs (kg) ........... 95.0 (43.2)

Tecumseh OH120 Maintenance Data

Cylinder Block and Valves

Cylinder Bore Inside Diameter (Maximum), in (mm) ........... 3.126 (79.400)
Cylinder Head (Max. Out of Flatness), in (mm) ........... 0.005 (0.127)
Intake Valve Clearance, in (mm) ........... 0.005-0.010 (0.13-0.25)
Exhaust Valve Clearance, in (mm) ........... 0.005-0.010 (0.13-0.25)

Engine Oil and Filter

Engine Oil Type (Summer) ........... SAE 30, 10W-30
Engine Oil Type (Winter) ........... SAE 5W-30
API Service Classifications ........... SF or SJ
Oil Capacity, qts (L) ........... 1.65 (1.56)
Air Filter Element Part Number ........... 32008

Carburetor Adjustments

Main Adjustment Screw ........... 1 turn
Idle Adjustment Screw ........... 1 turn
Low Idle Speed, rpm ........... 1600-1800
High Idle Speed, rpm ........... 3600-3900

Ignition System

Spark Plug Type ........... Champion RL82C
Spark Plug Gap, in (mm) ........... 0.030 (0.762)
Spark Plug Torque, Nm (ft-lbs) ........... 21 (28.5)

Service Intervals

Service Air Cleaner Element ........... Every 25 hrs
Change Engine Oil ........... Every 25 hrs
Clean Cooling Fins ........... Every 25 hrs
Check and Adjust Spark Plug ........... Every 100 hrs
Replace Air Cleaner Element ........... Every 100 hrs
Check Carburetor Adjustment ........... Every 100 hrs
Check and Adjust Valve Clearance ........... Every 200 hrs
Replace Spark Plug ........... Every 200 hrs

Tecumseh OH120 Service Specifications

Cylinder Block

Cylinder Bore (Standard), in (mm) ........... 3.125 (79.375)
Cylinder Bore (Maximum), in (mm) ........... 3.126 (79.400)
Connecting Rod Journal Diameter, in (mm) ........... 1.3750-1.3755 (34.925-34.938)
Connecting Rod Diameter (Maximum), in (mm) ........... 1.3765 (34.963)
Shaft Seat Diameter for Roller Bearings, in (mm) ........... 1.1865-1.1870 (30.137-30.150)
Crankshaft End Play, in (mm) ........... 0.001-0.007 (0.025-0.178)
Piston Skirt Diameter, in (mm) ........... 3.121-3.123 (79.273-79.324)
Piston Pin Diameter, in (mm) ........... 0.6876-0.6880 (17.465-17.475)
Compression Ring Groove Width, in (mm) ........... 0.0950-0.0960 (2.413-2.438)
Oil Ring Groove Width, in (mm) ........... 0.1880-0.1900 (4.775-4.826)
Ring Groove Side Clearance, in (mm) ........... 0.0015-0.0035 (0.038-0.889)
Ring End Gap, in (mm) ........... 0.010-0.020 (0.254-0.508)
Top Piston Land Clearance, in (mm) ........... 0.031-0.034 (0.787-0.864)
Camshaft Bearing Diameter, in (mm) ........... 0.6235-0.6240 (15.837-15.850)
Cam Lobe Diameter, in (mm) ........... 1.3117-1.3167 (33.317-33.444)

Cylinder Head and Valves

Cylinder Head (Max. Out of Flatness), in (mm) ........... 0.005 (0.127)
Intake Valve Clearance, in (mm) ........... 0.005-0.010 (0.127-0.254)
Exhaust Valve Clearance, in (mm) ........... 0.005-0.010 (0.127-0.254)
Valve Seat Angle, deg ........... 46
Valve Seat Width, in (mm) ........... 0.042-0.052 (1.067-1.321)
Valve Face Angle, deg ........... 45
Valve Face Width, in (mm) ........... 0.094 (2.388)
Valve Lip Width, in (mm) ........... 0.06 (1.524)
Valve Spring Free Length, in (mm) ........... 1.915 (48.641)
Valve Guides Diameter (Std), in (mm) ........... 0.312-0.313 (7.925-7.950)

Tecumseh OH120 Torque Specifications

Connecting Rod Screw or Nut, ft-lbs (Nm) ........... 15.0-20.1 (20.3-27.1)
Mounting Flange Cylinder Cover Screw, ft-lbs (Nm) ........... 7.2-9.2 (9.7-12.4)
Cylinder Cover Flywheel End, ft-lbs (Nm) ........... 8.4-10.9 (11.3-14.7)
Flywheel Nut, ft-lbs (Nm) ........... 10.1-13.4 (13.6-18.1)
PTO Shaft to Flywheel, ft-lbs (Nm) ........... 50.2-55.3 (67.8-74.6)
Spark Plug, ft-lbs (Nm) ........... 8.4-10.4 (11.3-14.1)
Intake Pipe to Cylinder, ft-lbs (Nm) ........... 18.4-23.4 (24.9-31.6)
Carburetor to Intake Pipe, ft-lbs (Nm) ........... 6.0-8.1 (8.1-10.9)
Air Cleaner Elbow to Carburetor, ft-lbs (Nm) ........... 4.0-6.0 (5.4-8.1)
Air Cleaner Bracket to Elbow, ft-lbs (Nm) ........... 2.1-3.0 (2.8-4.0)
Air Cleaner Bracket to Carburetor, ft-lbs (Nm) ........... 1.3-2.1 (1.7-2.8)
Tank Bracket to Cylinder (5/16'’ Lower), ft-lbs (Nm) ........... 1.3-2.1 (1.7-2.8)
Tank Bracket to Cylinder (1/4'’), ft-lbs (Nm) ........... 12.6-16.7 (17.0-22.6)
Starter-Recoil-Top Mount, ft-lbs (Nm) ........... 8.1-10.1 (10.9-13.6)
Starter-Electric-Straight Drive, ft-lbs (Nm) ........... 3.0-4.1 (4-5-6.8)
Rope Start Pulley Mounting Screws, ft-lbs (Nm) ........... 11.7-14.2 (15.8-19.2)
Rocker Arm Box to Cylinder Head, ft-lbs (Nm) ........... 4.1-6.3 (6.8-8.5)
Rocker Arm Cover and Breather (Screw to Stud), ft-lbs (Nm) ........... 6.7-7.6 (9.0-10.2)
Rocker Arm Adjusting Screw Lock Nut, ft-lbs (Nm) ........... 1.3-1.7 (1.7-2.3)
Rocker Box Cover to Mtg. Stud, ft-lbs (Nm) ........... 4.0-6.0 (5.5-8.0)
Magneto Stator Mounting Screw, ft-lbs (Nm) ........... 1.7-2.5 (2.3-3.4)
Blower Housing to Baffle or Cylinder, ft-lbs (Nm) ........... 6.0-8.1 (8.1-10.9)
Housing Baffle to Cylinder, ft-lbs (Nm) ........... 4.0-6.0 (5.4-8.1)
Blower Housing Extension to Cylinder, ft-lbs (Nm) ........... 6.0-8.1 (8.1-10.9)
Governor Rod Clamp to Rod (Screw and Nut), ft-lbs (Nm) ........... 6.0-8.1 (8.1-10.9)
Governor Rod Clamp to Lever (Screw and Nut), ft-lbs (Nm) ........... 1.3-2.1 (1.7-2.8)
Ground Wire to Terminal, ft-lbs (Nm) ........... 1.3-1.7 (1.7-2.3)
Toggle Stop Switch Nut, ft-lbs (Nm) ........... 0.4-0.8 (0.6-1.1)
Oil Drain Plug 3/8-18, ft-lbs (Nm) ........... 0.8-1.3 (1.1-1.7)
Oil Drain Cap, ft-lbs (Nm) ........... 6.7-8.3 (9.0-11.3)