Electric Motor Problem: Troubleshooting 4 HP 240 Volt Motor

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dwgumpher
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I have a 4 hp 240 volt single phase motor in a grain bin that drives an auger. The motor is to run in only one direction Counter clock wise. After about four to five hours of run time the motor will start to run backwards. I replaced the capciator thinking that may be the problem. The motor ran fine for about six hours and then reversed again. What else can I look for, the motor has worked fine for a period of six years until today?
 

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Normally a single phase motor that has an open starting winding or starting winding lead/capacitor will just sit and hum. In this case, you can manually turn the shaft and get the motor to spin up in either direction. I have heard of motors that will wind up themselves in some direction slowly at much reduced starting torque with a defective starting circuit. I would think this would draw enough current to trip the overload protection, but apparently not in some cases. Is there just a starting capacitor in this motor or is there a run capacitor as well? Do you have a make and model number?