I have a kenmore 80 series dryer that start and stop mid way during the drying time and do not always get hot to dry, please help me tell me how can I look at the motor to see if it need to be replaced or do I need a new dryer. Thanks in advance

These driers will do that when the lint builds up like concrete on the inside of the air ducts. Most people just clean it once a year and replace the belt and lubricate it, unless you just like buying new dryers. You need to totally tear it down and scrape out and wash all of the parts except the motor, which you vacuum out. Halfway doing it will not work. This includes the exhaust vent, all the way, even the outlet on the side of the house if you have one. You will also have to find the blown safety with an ohm meter if it stopped heating altogether. You cannot guess and just change parts. You can go to YouTube to see videos on how to take it apart, but do a very good job or it will fail again quickly. I would get a new belt and change it while you have it apart and get some white lithium grease and grease any bearings you find. You need to clean out a drier every two years, at least, according to the manual. All sensors work together by comparing temperature, so all need to be cleaned. You just unplug the wires from the sensors and remove ductwork that they are attached on and clean the entire thing with soap and water. Make sure you go all through the dryer and get all parts like the blower fan and housing, vacuum out motor well and clean exhaust. Mark all wires you unplug so you know where they go. This is an easier job than you would think. You need a meter to test any fuses that may be blown, which I strongly suspect is the case. You will see them on the schematic diagram.
See: Dryer vent cleaning prevents fires - YouTube (http://www.youtube.com/watch?v=A6wmD502-xE) and: Cleaning out a dryer with top lint cleanout - YouTube (http://www.youtube.com/watch?v=OBNDbyRm68M&feature=fvsr)
Cleaning out a dryer: By a woman 2 of 2 - YouTube (http://www.youtube.com/watch?v=a73HTFkcB90&feature=relmfu)
Manuals: https://dl.dropboxusercontent.com/u/8010163/Kenmore%20Dryer%20Manuals.zip