A rotary plow cutter shaft that does not turn is a relatively common failure, and the cause usually involves blocked power transmission or mechanical jamming. The following are common causes of failure, which can be investigated step-by-step from simple to complex:
1. Operational or connectivity issues (easiest to troubleshoot)
Failure to Properly Gear or Combine Power Take-Off Axles (PTO): Verify that the tractor is in the correct gear (usually low gear) and that the power take-off axle switch/handle is properly combined (some require the clutch to be depressed to combine).
Clutch Problems:
Not pressed to the bottom/incomplete separation: The clutch pedal is not pressed to the bottom or the clutch itself is faulty (e.g., damaged release bearing, pressure plate problem), resulting in power not being fully transferred to the transmission or PTO shaft.
Clutch slippage: Although rare and resulting in complete stalling, severe slippage can be characterized by weak or intermittent rotation.
The angle of the drive shaft is too large or wrongly installed: the universal joint drive shaft is not aligned with the marking of "square tube over square shaft" when it is installed, or the tiller is lifted too high, resulting in the angle of the drive shaft being too large beyond the safety range (usually specified in the manual, such as ≤30°), resulting in jamming.
Improper adjustment of three-point suspension: Improper adjustment of the left and right lifting rods or upper tie rods, resulting in tilting of the tiller or abnormal working angle of the drive shaft.
2. Stuck or damaged driveline (requires shutdown for inspection)
Drive shaft seized:
Damaged or seized universal joint cross shafts: This is a very common cause. A lack of oil, wear and tear, rust, or mud in the cross shaft needle bearings can cause seizing.
Deformed driveshaft: hitting a hard object causes the driveshaft to bend and stall on rotation.
Stuck or deformed drive shaft guard: The guard is crushed and deformed, directly rubbing on the drive shaft.
Gearbox failure:
Damaged gears: Internal gears are chipped, broken and jammed.
Bearing damage/seizing: The bearing of the gearbox input shaft, output shaft or intermediate shaft is seized due to lack of oil, wear and tear, overheating or contamination.
Lack of lubricating oil or deterioration of oil quality: Gearbox lacks oil or the lubricating oil is seriously contaminated or ineffective, resulting in overheating and damage to gears or bearings, resulting in seizing.
Internal foreign matter: Gear box into the metal foreign matter stuck gear.
The overload protection device works:
SAFETY PIN SHEARING: Most rototillers are designed with a safety pin at the gearbox input shaft or drive shaft. When the cutter shaft encounters significant resistance (e.g., hitting a hard rock, tree root), the safety pin shears off to protect the drive train. This is one of the most common causes and the easiest to fix (replacing the safety pin with a new one is sufficient, but the root cause of the overload needs to be eliminated first).
Friction Safety Clutch Slip Failure: Some rototillers use friction plate overload protection. If the friction plate is excessively worn, oiled, or under-pressurized, it will slip or even fail completely during an overload, manifesting itself as a failure to transmit power. Adjustment or replacement of the friction plate is required.
3. Stuck cutter shaft and working parts (need to focus on the cutter shaft area)
External tangling/clogging of cutter shaft：
Blade wrapped grass, rope, plastic film: a large number of tough weeds, rope, film, etc. tightly wound on the knife shaft or blade, forming a huge resistance.
Blade or blade shaft hitting hard objects jammed: the blade hits the large stones, cement blocks, roots and other hard objects in the ground, resulting in instant jamming of the blade shaft.
Blade deformed/broken jammed: The blade is deformed and scrapes the side plate or fender, or the broken blade is stuck between the blade holder and the side plate.
Internal failure of the cutter shaft：
Cutter shaft bearing damage/holding: The support bearings at the ends of the cutter shaft burn out and hold due to lack of oil, wear, seal failure, water and mud ingress or overload. This is a very common cause, especially in the case of paddy field operation or untimely maintenance.
Bending and deformation of the cutter shaft: The cutter shaft is bent due to strong impact (such as sudden fall in high speed, hitting a hard object), and when rotating, it rubs and jams with the side plate or gear box shell.
Knife seat damaged or loose jammed: Knife seat cracked, deformed or fixing bolts loose/dislodged, resulting in abnormal blade position jammed.
Deformation of the side plate or hood jamming the cutter shaft/blade： The side panels or rear cowling of the rotary tiller are deformed by collision and friction interference with the rotating cutter shaft or blades occurs.
4. Hydraulic system problems (affects lifting and indirectly leads to jamming)
Hydraulic lifting system failure stuck in the down position：Although it does not directly cause the cutter shaft to not turn, if the rototiller cannot be lifted due to a hydraulic failure and the cutter shaft is forced into excessively hard soil, it can also cause it to not turn due to excessive resistance at startup (which may be accompanied by a sheared safety pin at this point). Check hydraulic oil level, tubing, distribution valves, cylinders, etc.
Recommendations for troubleshooting steps
1. Confirm operation: Re-check the gear, PTO bonding status, and clutch operation.
2. Cut off power, safety first! Always turn off the tractor engine and remove the key.
3. Visual inspection:
Check for obvious deformation of the drive shaft and jamming of the guard.
Focus on checking the area of the knife shaft: whether there are tangled things? Does the blade hit something hard and get stuck? Is the knife shaft bent? Is the side plate deformed and rubbing?
Check whether the safety pin is broken (usually in the drive shaft universal joint fork or gear box input shaft flange).
4. Try turning manually:
Try to turn the drive shaft or cutter shaft carefully by hand (wearing gloves) or with a pry bar (be safe!). . If it turns but feels stuck, there may be a bearing problem or slight deformation.
If it does not turn at all, the jamming is severe and may be in the cutter shaft bearings, inside the gearbox, or severe wrap/impact jamming.
5. Disconnect in steps:
If the driveshaft turns but the cutter shaft does not, the problem is in the cutter shaft or gearbox output section.
Remove the drive shaft and turn the gearbox input shaft alone. If the input shaft can turn, the problem is in the gearbox output shaft or knife shaft. If the input shaft also can not turn, the problem is inside the gear box.
6. Check gearbox oil: Check the oil level and quality for metal shavings (indicating internal damage).
7. Check the bearings: Try to shake or rotate the cutter shaft to check the bearing clearance and whether the rotation is smooth, and whether there is any strange noise.
Summarize
The most common reasons for the knife shaft not turning are safety pin shearing, knife shaft winding debris, knife shaft bearings holding, drive shaft universal joints jammed, the blade hit a hard object stuck, and the gear box internal damage (bearings holding or gear damage). Be sure to start with simple operations and external inspections, and gradually work your way down to internal troubleshooting. If you do not have repair experience, especially when gearbox disassembly is involved, it is recommended that you contact a professional farm machinery repairer to handle the situation. Safety always comes first!
