How can you tell if starter is bad.

 

Apply 12 volts from a source that can supply high (100 amps) current and observe if it runs. There is a starter solenoid on the starter and if it actuates and its switch contacts are good, then I would expect to see the starter run.
The batt cable connects to the start solenoid switch and the other contact on the start solenoid switch goes to a large bolt on the starter. If you connect these bolts together with a large screwdriver, then you create a current path to the starter motor and it should run. If it doesn't, measure the voltage on the cable post when you jump the start solenoid. If it doesn't read 12 volts, then you have a defective batt cable, or bad battery post connection, or a defective battery. If it stays at 12 volts but the starter doesn't run, check the voltage on the frame of the starter motor. It should be 0 because the frame of the starter motor is supposed to be a good electrical connection (mechanical) to the engine which is connected to the battery negative post via a large braid from the rear of the left head to a bolt on the frame which also has the negative cable from the battery. Check to see if the braid is not broken and both connections on each end are bright and tight. Some auto parts places can test your starter motor. Find out if there are any near you and remove the starter and let them test it.