How to take apart a lawnmower engine

Written by mark o'brien
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How to take apart a lawnmower engine
Take apart your lawnmower engine. (fress cut grass image by Photography Freak from

When your lawnmower engine needs a serious overhaul including replacing piston rings, replacing engine block gaskets, welding a cracked engine block, replacing the crankshaft or any other major interior engine repair, you will need to take apart the engine. Small lawnmower engines are much less difficult to take apart than a car engine, but they still require some special tools and basic knowledge to ensure you won't damage the engine as you dissemble it.

Skill level:

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Things you need

  • Oil drain pan
  • Bucket
  • Pliers
  • Wrench set
  • Socket set and ratchet
  • Flywheel holder
  • Three arm gear puller
  • Rubber mallet

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  1. 1

    Unscrew the oil drain plug located at the base of the oil dipstick shaft or on the base of the oil pan. Use the proper sized wrench to remove the drain plug. Position the oil drain pan under the engine to capture all the used oil. Tighten the oil drain plug back into the engine block.

  2. 2

    Follow the hose under the gas tank to the side of the carburettor. Squeeze the spring clamp holding the hose onto the carburettor with the pliers and slide the clamp down the fuel hose several inches. Pull the hose off and point it into the bucket to catch the old gas.

  3. 3

    Remove the engine shroud from the top of the engine that is covering the flywheel. Use the proper sized wrenches to remove all the bolts around the perimeter of the shroud holding it onto the engine block.

  4. 4

    Pull the shroud off to expose the flywheel. Locate the magneto and governor bolted next to the flywheel. Unscrew the two bolts holding the magneto next to the flywheel with the correct sized wrench. The magneto is a half moon shaped magnet.

  5. 5

    Unscrew the single bolt with the correct sized wrench that is holding the governor flap into the engine block next to where the magneto was. Unhook the springs running from the governor flap to the throttle linkage.

  6. 6

    Fit the proper sized socket on the flywheel nut in the centre of the flywheel. Have a friend fit the flywheel holder over the fins on the engine, and have him hold the tool firmly as you unscrew the centre flywheel nut.

  7. 7

    Position the three armed gear puller over the flywheel. Hook the arms under the outer edges of the flywheel. Center the puller bolt in the centre of the puller over the crankshaft in the centre of the flywheel. Tighten the bolt on the puller with the proper sized wrench until the pressure pops the flywheel free from the crankshaft. Grab the flywheel key from under the flywheel which will be wedged into the crankshaft. Place the flywheel key in a safe place with the flywheel and flywheel nut.

  8. 8

    Unscrew the two bolts holding the throttle linkage onto the side of the engine and hooking into the eyelet on the carburettor. Unhook the throttle linkage from the eyelet on the carburettor.

  9. 9

    Unscrew the four bolts holding the carburettor onto the side of the engine block. Use the proper sized wrench to remove the bolts. Pull the carburettor off and peel the rubber carburettor gasket off the side of the engine block.

  10. 10

    Pull the spark plug cap off of the spark plug. Fit the proper sized socket on the head bolts holding the six to eight bolts into the cylinder head cover on the front of the engine. Unscrew all the bolts to remove the engine cylinder head cover and expose the top of the piston. Peel the head gasket off and set it with the cylinder head cover and head bolts.

  11. 11

    Flip the engine upside down to expose the base of the engine. Unscrew the bolts holding the oil pan onto the base of the engine. Pull the oil pan off the crankshaft to reveal the inside of the engine. Peel the oil pan gasket off the engine block and set it with the oil pan and oil pan bolts.

  12. 12

    Pull out the oil spinner wheel that's just set into the engine block.

  13. 13

    Locate the piston arm bolted around the crankshaft. Use the correct sized wrench to remove the two bolts holding the piston arm onto the crankshaft. Push the piston arm connected to the piston up and out of the cylinder. Finger tighten the piston arm holder back onto the piston arm and set it in a safe place.

  14. 14

    Tip the engine on its side. Tap the top of the crankshaft--where the flywheel was--with the rubber mallet to dislodge the crankshaft from the engine block. Pull the crankshaft out of the base of the engine.

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