Starters 101

I need a short primer so I know what I am looking at. The shop manual for the SAV has a number of things I can check but I have no point of reference. Have not been able to bench test yet as the 6v/12v power supply on my bench does not have the ability to generate the 65 amp no load draw of the motor...so it just hums. Keeping in mind that I have never had a starter problem before and only know what I can read in the manuals, can someone tell me what makes the gear on the starter move out (to engage) and in (to disengage) the ring gear and turn the engine? Mine (the gear) moves freely by hand although the spring on the shaft seems a little sloppy. I know little of electric motors and have to wonder if this isn't something better left to a shop? I have heard of starter solenoids but don't see a solenoid, other than the fact that the whole starter motor looks like a large solenoid. Can anyone give me the basics of starter operation beyond what is in the manual? Thanks!

What is the starter off of. Sounds like you have one from like an H or M farmall. If so, the drive is inertia driven, in other words when the armature start to spin the drive tends to stand still so it screws its way out on the shaft and when engine fires the drive turns faster than armature so it threads itself back again. You can just hook it up with a set of jumper cables to 6 or l2 volts what ever it is and then check current draw. I rarely check draw as I pretty well know how they should wind out. The most important thing with any starter is the condition of the bushings, wear and lubrication, and brushes for good clean contact on comutator bars. Of course other things like conditon of field coil soldered connections etc. Kind of shooting in the dark here not knowing which type of starter you are working on.

It is a little mysterious to the naked eye, Dave. pete 23's description of its operation is better than what I'd have come up with. The naked eye part comes in as part of what makes the gear on the motor move into the teeth on the ring gear. She shaft is machined with a slight helix to it. It is not round as it may appear to the eye. When you first put juice to the starter motor, it is spinning at a very high rate and the gear rides that helix (think of the loosest, most wobbly thread fit you can imagine) until it engages with the ring gear. And, again just as Pete described, the running motor will speed up the shaft on the starter motor to faster than it is being driven by electricity, and the gear will back off. There is typically a very light spring that will hold the gear back that will speed its pulling back and prevent the starter gear from vibrating out and getting into the ring gear while you are running.

A solenoid has taken different configurations over the years, but you can think of it as an electrically operated actuator that forces the starter gear into the ring gear. It operates only when the switch is held in the start mode. On a modern car, when it's working right, the starter motor operates only when you hold the key in the start position. That position powers the solenoid which, with electrical power, moves the starter gear into the ring gear. When your motor starts and you let the key switch fall back to the run position, it cuts off power not only to the starter motor but to the solenoid, which then allows the starter gear to return to its rest position.

Clear as mud?

I will add some to the info:
The motor is a series wound high torque DC motor.Series means it has a single path for electricity. From the terminal on the outside (or contact stud under the start switch) the current flows through the field windings (first one winding, then the other) then it goes to the brushes where it then travels through armature windings, and back to brushes to ground. This motor type is designed to operate one direction only as a starter motor. and will not go backwards with a change in polarity. They are intermittent duty. meaning they will get hot if used for long periods (one minute), or for more than about 10% of total time, in use as a starter.
They are also very close to zero resistance. with an ohm meter applied to the post and ground. They can draw as much as 500 to 600 amps on larger equipment. more like 250 to 275 for your engine.
A starter solenoid is not on your tractor. It has a mechanical switch, and as described below an inertial drive pinion.
A solenoid is an electrical to mechanical (linear motor) that moves some device, valve, or starter pinion. They often also provide high current switching to the starter allowing much smaller wires for the push button or key. Yours has a rod to activate the mechanical switch.
A starter relay (often mistakenly called a solenoid) is a small can like device on the starter that is only a remote switch, not a pinion moving device. It has only wires connected to it. Jim

Sorry Pete! I usually start every post with a description of what I am working on. The tractor is a Super AV but you were right on with everything else. I can picture how it works based on what you told me...thanks much!!!

Nope...crystal clear. Either I am getting better at this stuff or these may be the best set of responses to a question I have seen in a good while! Thanks for expanding on that, you described the whole shaft/gear/spring thing to a T. Makes great sense to me now...thinking the problem is in the OTHER end of the starter.

Thanks Jim! I understand everything you are saying and it is excellent reference material for current use and for my archives. Between these three responses I feel like I have been thru a course series...Starters 101, 201, etc. Your input is very much appreciated!

". . . for current use," he sez. Nyuk, nyuk!

Oh brother! How did that one get by me? I think there is strong resistance to pun fests on this board so we better pull the plug on this one.

(They're just not funny when I TRY to do them!)

Ohm y, I hadn't thought of that.