Things You'll Need
Large piece of cardboard
Cheater bar or wood block
Valve spring compressor
Lawnmower crankshafts can get bent from the blade hitting a solid object while mowing, such as a tree root or rock. A crooked crankshaft can occasionally be straightened by heating and bending in a vice, but a severely bent shaft might have to be replaced. The connecting rod pin on the crankshaft will eventually wear enough to require a replacement crank after years of use.
The shaft is cast as one piece of steel, and much of the engine must be disassembled to get it out. Lawnmower engines in the 3 to 6-HP range require very similar procedures for crankshaft removal.
Remove engine fluids
Place a drain pan next to the lawnmower. Tilt the mower enough to gain access to the oil drain plug, and unscrew it with a socket wrench. Drain the oil from the lawnmower engine.
Use a pair of pliers to compress the fuel hose clamp where it attaches to the fuel tank. Remove the fuel hose from the gas tank and drain all of the gas out. Remove the gas cap and turn the mower on its side for an alternate drain method.
Remove the air filter housing, fuel tank or fuel tank/carburetor assembly.
Remove engine attachments
Use a Phillips-head or flat-blade screwdriver to unhook the throttle cable and engine cut-off cables, if so equipped.
Remove the oil tube dipstick, if so equipped.
Remove the pull-start cowl; on electric start models, remove the metal shroud which is bolted on the top of the engine.
Disconnect the spark plug wire. Remove the ignition module or magneto and remove the spark plug.
Tap the round starter clutch (if so equipped) moderately with a rubber hammer in a counterclockwise direction to unscrew it from the crankshaft. Take the clutch off.
Unbolt the flywheel. Use a cheater bar or piece of wood to stabilize the flywheel while loosening the bolt. Be careful to not break any of the cooling fins.
Pry under the flywheel with a large flat-blade screwdriver while tapping on the crankshaft end with a rubber hammer. Use a flywheel puller if it still won't break free. Remove the flywheel. Take out the shear pin from the crankshaft slot.
Turn the lawnmower on its side.
Wear work gloves, and grasp the blade along an un-sharpened section. Hold the blade firmly while rotating the blade bolt with a large wrench to loosen. Remove the bolt and blade.
Turn the mower upright. Locate the engine mount bolts which hold the engine and deck together.
Remove the bolts and the engine from the mower. Place the engine on a workbench for a more comfortable work space.
Remove Valve Spring
Remove the two small screws holding the valve cover in place and take off the cover.
Clamp the valve spring compressor tool onto the top of the spring on one end and between the metal washer and the spring end on the other. Compress the spring.
Jiggle the metal washer until it slides off through the notch on its edge. Remove the washer and slowly release the spring. Do not remove the spring from the chamber. Repeat this process with the other spring.
Remove the lower engine case on the blade side of the engine. Slide the cover off gently—oil may run out as you take off the cover.
Grasp the camshaft gear and pull it free. Remove it.
Bend the retaining tabs downward from around the connecting rod end cap bolts. Unscrew the bolts and take off the rod end cap.
Press the connecting rod upward so the piston slides to the top of the cylinder. Turn the crankshaft until the connecting rod pin points away from the cylinder.
Slide the crankshaft toward you and remove it from the engine.
Wash the engine exterior with engine cleaner and a spray nozzle before beginning. Place a large piece of cardboard underneath and around the work area.
Wait until the engine is cool before attempting this procedure. Keep your head away from the flywheel when breaking it free—it may suddenly snap upward. Use work gloves when removing the camshaft—the gear is rather sharp.
Steve LaNore has written and produced broadcast reports/specials and printed literature since 1985 and been a Web writer since 2000. His science blogs/reports can be seen on the Web site of KXII-TV. LaNore is a five-time award-winning meteorologist and member of the American Meterological Society as well as a Certified Broadcast Meteorologist sealholder. He holds a Bachelor of Science in meteorology from Texas A&M University.