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Testing the Electrical System

What is the procedure for testing the engine's electrical system?
Testing the Electrical System

Small engines that start with a key require an electrical system to charge the battery and to power onboard electrical devices. If you hear a groan or just a click when you try to start a small engine equipped with an electric starter motor, your electrical system may be the source of the problem. Electrical problems can also keep onboard electrical devices from operating. The proper test can help you identify the source of the problem. If you need assistance in identifying the style of alternator installed on your engine, please download our Alternator Identification Chart or Alternator Specifications (PDF).

When testing an alternator or other electrical system component, use the AC volts/DC amps meter settings chart to determine the correct test. The chart includes the most common electrical systems on Briggs & Stratton engines and illustrates the proper way to attach a multitesterClamp Style Digital Multi-Meter
Clamp Style Digital Multi-Meter
(service part number 19602) to your engine. If you own an engine produced by another manufacturer, ask your authorized service dealer how to connect the alternator for testing.

This section also explains how to replace your stator, if necessary. On most models, the stator is mounted under the flywheel and is not difficult to replace once the flywheel is removed. On some walk-behind lawn mowers, the stator is mounted outside the flywheel, making replacement even simpler.

Selecting The Right Test For Your Alternator
  1. With the engine off, locate the thin wire(s) extending from beneath the blower housing. These wires attach to the stator under the flywheel and deliver the electrical current from the stator to the battery and other electrical devices.

  2. Note the color of the wires (scrape away any engine paint to identify the true wire color), as well as the color of the wire connector, typically an inch or two from the blower housing. For a Briggs & Stratton engine, find the same wire/connector combination on the AC volts/DC amps meter settings chart. The chart tells you the type of test to perform (AC Volts or DC Amps), how to set your multitester leads and the correct engine test speed and multitester readings.

  3. Use the appropriate test procedure for your engine listed below. If the wiring on your engine is not on the chart, ask your Authorized Dealer how to test your equipment.

Battery Safety

Small engines typically use lead-acid batteries, which store electrical energy using lead plates and sulfuric acid. The electrolyte fluid in the battery loses its sulfuric acid and gains water as the battery is discharged.

Battery electrolyte is extremely corrosive and can cause severe burns to eyes and skin. Batteries produce hydrogen gas that can cause an explosion if ignited by a spark or open flame. Minimize safety hazards by observing these precautions:

  • Follow the manufacturer's recommended procedure for charging, installation, removal and disposal.

  • ALWAYS hold a battery upright to avoid spilling electrolyte.

  • Wear protective eyewear and clothing when handling batteries.

  • If electrolyte spills on skin or splashes in an eye, flush immediately with lots of cold water and contact a physician immediately.

  • Service batteries in a well-ventilated area, away from sources of sparks or flames.

Conducting An AC VOLTS Test

If your engine requires an AC VOLTS test, set the tester's dial to AC VOLTS and follow these steps:

  1. Insert the black multitester lead into the tester's COM receptacle. Connect the other end to ground, such as an engine bolt or cylinder fin, or to the double connector on the stator output wires.

  2. Insert the red lead on the multitester into the tester's AC VOLTS receptacle. Connect the red lead to the appropriate stator output wire (image A)AC Volts Test 106A
    Image A
    .

  3. Start the engine and let it run for several minutes to read its operating temperature. Then, using a tachometerDigital Tachometer & Hourmeter 19598
    Tachometer
    (service part number 19598), set the engine test speed and check the reading on the tester. Replace the stator if the reading is incorrect.

  4. Turn off the engine and disconnect the multitester from your equipment.

Conducting A DC AMPS Test

If your engine requires a DC AMPS test, set the tester's dial to DC AMPS and follow these steps:

  1. Insert the black multitester lead into the tester's COM receptacle. Connect the other end to the battery's positive terminal. (NOTE: The battery must be grounded to the equipment frame of the engine block to create a complete circuit.)

  2. Insert the red lead on the multitester into the tester's AMPS receptacle. Connect the red lead to the appropriate stator output wire. (image B)DC Amps Test 106B
    Image B
    .

  3. Start the engine and let it run for several minutes to reach its operating temperature. Then, using a tachometer, set the engine test speed and check the reading on the multitester. An incorrect eading indicates that the stator, diode or regulator should be replaced.

  4. Turn off the engine and disconnect the tester from your equipment.

Replacing A Stator Under The Flywheel

In most cases, you need to remove the blower housing, rotating screen, rewind clutch and flywheel to get to the stator (see "Inspecting the Flywheel & Key".) If your stator is mounted outside the flywheel, follow the instructions under "Replacing An External Stator."

  1. With the flywheel removed, note the path of the stator wires, under on coil spool and between the starter and starter drive housing.

  2. Remove the ground wire or rectifier assembly (if equipped) from the starter drive housing. Then, remove the stator mounting screws and bushings.

  3. Before installing a new stator, locate the stator wires against the cylinder and make sure the wires remain clear of the flywheel (image C)Replace Stator 106C
    Image C
    .

  4. Install a new stator assembly, making certain the output wires are properly positioned. While tightening the mounting screws, push the stator toward the crankshaft to take up clearance in the bushing. Then, tighten the screws to 20 inch lbs.

  5. Reinstall the flywheel, screen and blower housing. Then, attach the ground wire or rectifier assembly (if equipped) to the drive housing.

Replacing An External Stator
  1. Disconnect the stator output wire from wires leading to the battery or other electrical devices.

  2. Rotate the flywheel until the magnets are positioned away from the stator. Then, loosen the stator mounting bolts and remove the stator from the engine (image D)Remove the Stator 107D
    Image D
    .

  3. With the flywheel magnets positioned away from the stator, install the new stator, leaving a wide gap between the stator and flywheel. Tighten one of the mounting bolts.

  4. Reattach the stator output wires. Then, follow the procedure for "Adjusting The Air Gap On An External Stator", below.

Adjusting The Air Gap On An External Stator

The gap between the stator and the flywheel must be set precisely for the stator to function properly. Many stators require a .010" stator air gap. Consult your Briggs & Stratton Authorized Dealer or our Engine Check Chart (PDF) for the proper gap for your stator.

  1. Rotate the flywheel until the magnets are positioned away from the stator.

  2. Loosen both stator mounting bolts and move the stator away from the flywheel. Then, tighten one of the mounting bolts.

  3. Place a shim or microfiche card of the proper thickness between the stator and the flywheel (image E)Set Air Gap 107E
    Image E
    .

  4. Turn the flywheel until the magnets are adjacent to the stator.

  5. Loosen the tightened bolt and let the magnets pull the stator until it is flush with the shim.

  6. Tighten both mounting bolts to 25 inch lbs. (image F)Tighten Mounting Bolts 107F
    Image F
    .

  7. Turn the flywheel while pulling on the shim to release it.

For related information, please visit our Electrical Diagram FAQ.


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