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Inspecting the Flywheel & Key

How is the flywheel and key inspected?

Inspecting the Flywheel & Key

The flywheel on your small engine was originally designed to store the momentum from combustion to keep the crankshaft turning in between the engine's power strokes (see "Compression System").

But the flywheel on today's small engines serve several other purposes. The fins help cool the engine by distributing air around the engine block (see "Lubrication & Cooling System"). The fins also blow air across the air vane on a pneumatic governor, maintaining the desired engine speed (see "Governor System"). Magnets mounted in the outside surface of the flywheel are required for ignition. On engines with starter motors, lights or other devices, magnets mounted inside and outside the flywheel are at the heart of the electrical system (see "Electrical System").

Finally, if a lawn mower or tiller blade hits a rock or curb, the flywheel key can sometimes absorb the damage, reducing repair costs significantly. Always check for damage by removing the flywheel to inspect the key and the keyway, the key's slot on the crankshaft. The soft metal key must eliminate play between the flywheel and crankshaft.

Removing The Flywheel
  1. Disconnect the spark plug lead and secure it away from the spark plug. Then, loosen the bolts holding the shroud in place and remove the shroud.

  2. If the engine is equipped with a flywheel brake, remove any cover and disconnect the outer end of the brake spring (image A)Removing Flywheel 99A
    Image A
    .

  3. If the flywheel is equipped with a flywheel clutch, remove it with a flywheel clutch tool while holding the flywheel with a flywheel holder or a flywheel strap wrench. If the flywheel is attached with a nut, use the flywheel holder as a brace, and remove the flywheel retaining nut with the appropriate socket (image B)Removing Flywheel 99B
    Image B
    .

  4. With the flywheel nut threaded onto the crankshaft, install a flywheel puller so its bolts engage the holes adjacent to the flywheel's hub (image C)Flywheel
    Image C
    . If the holes are not threaded, use a self-tapping flywheel puller or tap the holes using a 1/4 X 20 tap.
    CAUTION: Never strike the flywheel. Even a slightly damaged flywheel presents a safety hazard and must be replaced.

  5. Rotate the puller nuts evenly until the flywheel pops free. Then, remove the flywheel and key.

Inspecting The Flywheel And Key
  1. Check for cracks on your crankshaft or broken fins on the flywheel. Replace them if you find such damage. The tapered sections must be clean and smooth, with no play between the two.

  2. Inspect the keyway and flywheel (image D)Removing Flywheel 99D
    Image D
    for damage. Slight burrs may be removed with a file. Then, make certain there is no play or wobbling when the flywheel is placed on the crankshaft.

  3. Inspect the flywheel key. If there are any signs of shearing or if you have doubts about the condition of your flywheel key, replace it. It's simple and inexpensive.

Installing The Flywheel

First, obtain a new flywheel key designed for your make and model from your Briggs & Stratton Authorized Dealer.

  1. Place the flywheel on the crankshaft and look through the flywheel hub to align the keyways on the flywheel and crankshaft.

  2. With the flywheel in place, place the key in the keyway; it should fit securely. If you feel play, check to see if the key is upside down. Debris can also prevent the key from seating in the keyway.

  3. Once the key and flywheel are securely in place, reattach the flywheel nut or clutch. Consult your Authorized Dealer or our Engine Check Chart (PDF) for the torque specifications for your make and model.

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