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Engines Buyer's Guide

As the nation's largest supplier of replacement engines, Northern is sure to have the one you need. Our replacement Engine Buyer's Guide, helps you select the engine with the right specifications and horsepower that gets you back on the job. If we don't have what you need, we can special order any engine made by Briggs & Stratton, Honda or Kohler.

Selecting a Replacement Engine

Northern Tool + Equipment can match 95% of small engines correctly by simply knowing the horsepower and drive shaft information: diameter, length and type of shaft (e.g., 5/8in. x 2 7/16in. Threaded).

Finding Your Mower's Model Number

You can try getting the model number from the information plate on the old engine, then ask us to match that model number. That may not be possible, since model numbers change when manufacturers adapt engine specifications to meet new requirements from the EPA (Environmental Protection Agency) for most types of small engines.

Engines: What to Look For

Note the horsepower of the engine you are replacing. If you do not know the horsepower exactly, that's OK since most engines within a power range have a similar pattern for the bolts that mount the engine. For example, most 3 to 5 HP engines have the same bolt pattern.

Consider how you will be using the engine. For a homeowner application, for example, a standard engine will work great and will have a long, useful life. If the new engine will be used in an industrial or commercial application, we recommend you step up to an I/C (Industrial/Commercial) or other engine with cast iron cylinder sleeves to withstand the wear and tear of prolonged use.

Another consideration is the size of the engine compartment. Sometimes with a model change, the manufacturer will reposition the gas tank or adjust some other feature that may affect its compatibility with your equipment. This is rarely a problem unless you are moving up to a larger engine for more power.


Horizontal Engine shaft

Horizontal engines have the drive shaft on one side and are commonly used for water pumps, generators, tillers and other general-purpose applications.

How to Measure Horizontal Engine Shaft

Vertical Engine shaft

Vertical engine shafts protrude from the bottom and are ideal for propelling the cutting blades on walk-behind and riding lawn mowers.

How to Measure Vertical Engine Shaft

Features to Consider

Recoil (or rewind) starting system is operated by pulling a rope. A strong tug spins the flywheel fast enough to generate the voltage necessary for ignition.

Electronic starting system relies on battery power and a starter motor to ignite the combustion process that starts the engine. Some electric start engines have recoil backup in the event of battery failure.

OHV (Overhead Valves) engines have the valves installed in the cylinder head so they face the piston and offer greater efficiency. A more symmetrical combustion chamber means more efficient burning of the air/fuel mixture.

V-Twin Design has 2 OHV cylinders operating in the combustion chamber, considerably reducing vibration. Crankshaft size is very important to know when replacing an engine. You want to match the existing engine's shaft size with that of the new engine to ensure a proper fit and top performance.

Gear ratio takes into consideration the equipment's application and the speed of the engine. On most small engines, the crankshaft will make 3600 revolutions per minute (RPM). In some applications — cement mixers, for example — this speed would be too high. If the engine's speed were reduced to keep the cement in the mixer, the engine would have to run at almost idle, thereby not taking advantage of the torque produced at top no-load speed (3600 RPM). Engines with a 6:1 gear ratio have a gear box that is integrated with the engine's crankshaft, allowing the engine to run at top no-load speed and still utilize the full torque of the engine. Thus, for every 6 turns of the crankshaft, the gear box and the gear boxes' shaft would turn 1 time for a final output of 600 RPM.

Low-Oil Level system causes the ignition to ground, stopping the engine (or preventing it from starting) in the event insufficient oil is in the crankcase.

Mechanical governor uses gears and flyweights inside the crankcase to sense speed and detect changes in the load, adjusting the throttle to compensate.

Pneumatic governor uses an air vane as a speed-sensing device. This air vane registers the change in air pressure around the spinning flywheel. Not as reliable as a mechanical governor.

Cast iron cylinder sleeve, piston and related components withstand wear while providing improved oil consumption for extended engine life. Because of their durability, cast iron cylinder sleeve engines are a good choice for professional or commercial applications.

Splash lubrication system directs oil to moving parts by a splashing motion. For example, oil is splashed to bearing surfaces with a dipper or slinger. A dipper is attached to the connecting rod that splashes oil from the oil reservoir as the piston travels up and down in the cylinder. A dipper can be used on both horizontal and vertical engines. The slinger, used on vertical crankshaft engines, consists of a spinning gear with paddles and is driven with the crank gear or cam gear. As the slinger gear spins, oil is discharged by the paddles and splashed throughout the crankcase.

Still need help?
Email our product experts, or Call 1-800-221-0516 our 24-hour sales line.