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I have had starters do two things that could be your problem. One is they can have a dead spot on the commutator, the other is they can have a short that pulls the battery down so much that it cannot turn the starter. Trouble shooting systems (electrical or otherwise) MUST be methodical or you waste a lot of time "running in circles" and not solving the problem. When I was trouble shooting problems on a main frame computer, I often would keep a "log" of what I had checked so I would not "get lost" in chasing a problem around. You also need the RIGHT test equipment, in your case, a hygrometer to check the battery - easy way to be sure it is charged, and a volt/ohm meter. Get a cheap ($10) one from Wally world or the shack that is ANALOG NOT digital. Digital can often be impossible to read when the voltage has low frequency noise on it, even though it is supposed to be direct current. First you should check the battery with the hygrometer, all cells should show good. Next I'd check with the voltmeter to see if you are getting voltage through the relay to the starter. As Wendell suggested, you may not have a good ground on the battery. OR you could have corrosion in between the cable clamps and the battery terminals. Start by reading the voltage directly off the battery terminals. Then see what you get from the starter terminal - after the relay - to the starter case when the relay is closed. WATCH OUT!! be SURE the tractor is out of gear - I have formed a habit of "shaking" the gear shift EVERY time before it hit the starter if I am standing next the tractor. You should have almost full battery voltage at the starter terminal measured to the starter frame. Anything less means that you have a bad connection some place. It could even be between the starter and the engine block - a poor grounding of the starter. If you suspect this, you might use jumper cables. One side going to the starter terminal and the other side going to the starter case. OUT OF GEAR WARNING!!! Again! Otherwise finding where the bad connection is is a matter of "back tracking" until you find a place where on one side you see full battery voltage and on the other side you see much less - each time with the starter as a load - i.e. starter relay closed so you are pulling current through the starter. Try to make each test as quick as possible so you do not drain the battery or over heat the starter. That reminds me of you saying that the coil is hooked directly to the battery. I hope you disconnect it when you are not trying to start the tractor. And for the tests above, I would leave it disconnected. Got have the engine turning FIRST before it is time to worry about spark - first things first! :-) If you are getting (almost full) battery voltage to the starter, then you need to be sure the starter turns free. I'd pull the starter. WATCH OUT!! you can pull the end off which allows the brushes to drop in so it is a BIG chore to get them back on the commutator. Someone has said to loosen the two bolts and pulling on the body of the starter pull it back so you have a gap between it and the motor. Then take the out side bolt loose from the block and put a nut on it that you then tighten up - it seems to me like it would help to add some washers under the head so you can get the nut tight with out the bolt hitting the block. With the starter out you can check that it turns free and with jumper cables actually run it. If that all checks OK, then the next thing to see is that the engine is free to turn. I'll end there and wait to see what you find out. Regards,
Larry
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