Hi Y'all,

I've been working on a different project and had to recondition a starter. While I was taking them apart, I figured I would share the photos. Think of this as a crash course in what is inside a starter (and why you shouldn't fear taking one apart to troubleshoot problems.)

Here's a typical GM starter. This one is specificly off of a mid 80's V8, but the design is pretty much universal since Delco put one into production in 1912 for Cadillac.



Ok, now take out five screws (three on the solenoid and two in the motor case) and the starter comes apart showing it's guts:



The basic parts of the starter are an electric motor with a gear that slides on the motor's shaft. When power is applied to the starter motor, the pinion gear slides out and engages the big ring gear attached to the crankshaft of the engine. In GM cars, that big ring gear also doubles as a flywheel (flexplate) to balance the motor and connect it to the transmission.

A key component of the starter is the overrun clutch (what used to be called a "Bendix" drive..same function, different design) that keeps the starter from being turned by the engine when it starts running. It only transfers power in one direction (clockwise rotation) and spins free in the other direction (counter-clockwise). Without it, the starter's pinion gear might get stuck in the teeth of the flywheel while the engine is running. In this example, the pinion and flywheel form a 17:1 reduction gear with a 153 tooth flywheel and a 9 tooth pinion gear on the starter. So, if the engine coughs to life and spins up to idle at 800rpm, the starter stuck in the flywheel is going to be spinning at 13,600 rpm...it will not live long doing that.

Another important part is the starter solenoid. It moves the pinion gear into the flywheel so the gear teeth mesh. It also makes the electrical contact that puts power to the starter motor to make it spin. The ignition switch in your car cannot handle enough power to run the starter motor (it take a lot of current to spin that motor.) All it does is put power to the starter solenoid. Contacts within the solenoid carry that heavy current from the battery to the starter motor. A coil spring around the solenoid plunger pulls the pinion gear off the flywheel when power is cut to the solenoid.

Here's the pinion gear in the nose of the starter in it's retracted position (starter is not engaged):



When the starter is about to start spinning the motor, here's where the pinion moves to:



And with the guts of the starter layed out for the world to see, here's how the parts relate to each other when the starter is off:




And again, the starter on:

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Bye Bye 1990 Bonneville LE... Now it belongs to my daughter
In the Garage: 2009 Subaru Outback, 1987 Camaro, 2006 SV650S, 1995 Regal 182 "ASANAGI", 1962 Ford Galaxie 500, 1995 Ford F150 XL 4WD, 1953 Farmall Cub

With that said, When the starter doesn't work, there are really only three possibilities:

1.) Not enough power is reaching the starter (weak battery, bad electrical contacts)

2.) Starter solenoid is burned out

3.) Starter motor is damaged/worn out.

The first one has nothing to do with the starter. For example, you turn the key in the ignition and the lights dim, the starter goes "clickity click click" and the motor doesn't turn.... the starter isn't bad, it may not be getting enough juice to operate the starter solenoid, or the solenoid energizes, but there's not enough current available from the battery to spin the motor.

When the solenoid goes bad (it's just a coil of wire and a pair of electrical contacts) the starter just doesn't work at all..turn the key and nothing happens.

There are only three electrical connections on the solenoid:



The big terminal is getting power from the battery (the entire body of the starter and engine block is the ground return back to the battery.) The smaller terminal on the right is the wire from the ignition switch. Put power to that terminal and the solenoid energizes and pulls the plunger at the other end. The third terminal at the bottom feeds power to the brushes of the starter motor. In most applications, the fourth terminal (on the right side) is not used.

If you think the solenoid is bad, hook your test light up to the ignition switch terminal and turn on the key to the start position. If the test light comes on, then you are getting power to the starter solenoid. Next test the motor contact. When the key is turned on, you should hear a "click" from the starter solenoid, and see the test light come on, confirming that power is getting through the starter solenoid to the starter motor.

The starter solenoid is easy to replace. It comes off the starter and can be done on the car (though it is probably best to take the starter off the car, then replace the solenoid while the starter is on your workbench.) You take off the three screws: two on the case of the solenoid, one connecting the solenoid to the starter motor's brushes. Rotate the solenoid until the key tab is free of the motor case and it will come away in your hand. Don't loose the big return spring, you'll need it later when you put it back together.

With the solenoid out of the way, the third electrical problem with the starter revolves around the brushes and commutor:



While these can be replaced, if they go bad or get worn out, it is usually time to turn the copper contacts on the armature of the starter motor. This gets complicated since it requires a lathe to do it right. If the problem involves the pinion gear, overrun clutch, or the brushes it is time to scrap the starter motor for a new one.

Hope this helps those who never peeked inside the starter to understand how it works.

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Bye Bye 1990 Bonneville LE... Now it belongs to my daughter
In the Garage: 2009 Subaru Outback, 1987 Camaro, 2006 SV650S, 1995 Regal 182 "ASANAGI", 1962 Ford Galaxie 500, 1995 Ford F150 XL 4WD, 1953 Farmall Cub

Nice illustrated article, Curt!

It definitely takes the mystery out of starter motors for those that are unfamiliar.

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White Horse. 230K miles, It just keeps on kickin'

Like Mike said... Thats really good to see...

Have any gear reduced units laying around?

Sorry, only owned one Tilton mini-starter...sold it off years ago as being more trouble than it was worth.

For the rest, what Don is talking about is a starter that doesn't have the pinion gear on the same shaft as the electric motor. Instead, a set of gears run as a transmission, to further reduce the speed the starter spins and multiply the torque. This is handy on engine with small flywheels or big static compression in the cylinders...the starter needs even more leverage to spin the motor. The starters are usually smaller and lighter than a stock starter (a handy feature in a tight engine compartment with tucked in exhaust headers.) The down-side is the slow speed the engine turns...it needs to be a high compression motor or the cranking speeds can be too slow to light off a cylinder and start the engine.

The reduction gears can be several styles. A planetary gear is common, as are seperate shafts for the motor, pinion, and any idler gears in between the two.

Another style of starter is a "direct drive" starter. There is no solenoid, the pinion gear is always engaged in the flywheel. Only the overrun clutch to keep it from self-destructing. These are commonly used on motorcycles because the starter is super-light in weight, and the engines are really easy to turn over.

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Bye Bye 1990 Bonneville LE... Now it belongs to my daughter
In the Garage: 2009 Subaru Outback, 1987 Camaro, 2006 SV650S, 1995 Regal 182 "ASANAGI", 1962 Ford Galaxie 500, 1995 Ford F150 XL 4WD, 1953 Farmall Cub

I would add:

4.) Pinion gears are damaged.

Somehow my ex stripped the pinion gears off a Chevy 305. Grrrr.

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My other car is a Trans Am

I finally got a spare PG style starter. When I take it apart, I'll post the pictures of it's guts for comparison. Biggest difference is in the nose of the starter, with the motor driving a set of planetary gears to reduce the running speed and multiply the torque of the starter before it gets to the pinion gear. (kinda like a baby transmission inside the starter.)

As to stripping the pinion gear...uh, umm,....yeah...that too..in addition to breaking the teeth out of the ring gear

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Bye Bye 1990 Bonneville LE... Now it belongs to my daughter
In the Garage: 2009 Subaru Outback, 1987 Camaro, 2006 SV650S, 1995 Regal 182 "ASANAGI", 1962 Ford Galaxie 500, 1995 Ford F150 XL 4WD, 1953 Farmall Cub

Very cool write-up. Thanks!

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-Joshua-

Does anyone know where you can get solenoids for the 3800 starters?

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2006 Chevy Monte Carlo SS

I swear I would've taken pics if I wasn't in such a hurry to fix it! LOL. She stripped all the teeth off of the pinion and broke four teeth off of the flywheel. I was so friggin stunned that I couldn't chew her out for it.

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My other car is a Trans Am