Not all grinding noises signal trouble. The hydraulic transmissions on many Craftsman riding mowers and lawn tractors normally make some rumbling and grinding noises. Self-propelled walk-behind Craftsman lawnmowers also make a grinding sound when pushed with the drive disconnected. Sudden changes in the sounds a mower makes, or new and unusual grinding or screaming sounds, often do indicate mechanical problems. Lubrication and cleaning might resolve the issue quickly. Don't operate the mower if you suspect damage.
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Grinding sounds often originate in the mower's transmission and might be the normal sound of gears meshing. The many different models of Craftsman mowers use a variety of transmission systems. Following the lubrication guidelines as given in the owner's manual prevents many problems. Noisy start-ups after a winter-long storage might result from cold grease that hasn't completely covered the transmission gears. On some models, a worn bearing at the input of the transmission might leak transmission grease, causing smoking and a grinding noise during operation. Servicing a mower transmission requires some mechanical experience. Professional repairs by a Craftsman technician can prevent more problems.
Momentary screeching and screaming sounds emitted when the mower deck engages might come from power take-off clutch discs briefly slipping or from loose deck belts. Deck belts elongate and loosen as they age and need frequent adjustment. Tension mechanisms might not fully engage a worn drive belt even when set at maximum. Jammed belt pulleys and clogged mower decks can also put so much drag on the blades that belts slip and burn. Bent or unbalanced mower blades put extra stress on bearings and cause strong vibrations that can rattle machine parts and cause intermittent grinding sounds.
Worn bearings about to fail completely often make grinding noises, as well as unusual vibrations. The mandrels holding the mower deck's cutting blades contain two bearings that need frequent lubrication to keep the bearings working properly. As bearings dry and overheat, seals fail and dirt enters the mechanism. Bearings in extremely poor condition can make grinding or screaming noises and might drop the blade out of the deck. With the mower stopped and safely parked, check for worn deck bearings by grasping a blade and shaking it. Replace bearings with unusual play, but don't replace the entire mandrel unless the housing shows damage, according to ManageMyLife.com.
Walk-behind mowers with single blade decks can sustain serious damage if the blade catches a large rock or a stump hidden in tall grass. An impact strong enough to bend the crankshaft jams the crankshaft against its bearing, causing vibration, noise and overheating. A bent crankshaft can't be repaired. Damaged mowers might show the same general symptoms but not for the same reason. Remove the blade from the machine and run the mower briefly, suggests ManageMyLife.com. Running the mower without load can cause more damage, so stop the mower after a few seconds. If the mower ran smoothly without the blade, look for problems in the deck or engine housing.