Classic Lincoln Automobile Restoration
Lincoln Model L Starter-Generator Detail Information
Model L DELCO 193C

The following notes show the DELCO 193C model L starter-generator unit. Information presented is accurate at the time of posting. As always, the final decision on whether to plate parts in chrome or nickel is at the province of the restorer

The Starter-Generator assembly used on model L Lincolns was the DELCO model 193 and in mid 1929 DELCO introduced the model 193C. It is both a starter, used to turn over the engine as well as a generator to charge the battery while the engine is running. This article examines its basic theory of operation, some practical maintainance tips and adjustments, and for those seeking a challenge, tips on rebuilding it. However, if youíre uncomfortable with dissassembling electrical devices, then perhaps it might be best to have a professional service your unit.

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Theory. When an electrical current flows through a wire or a conductor, a magnetic field is created around it. Notice the term used is current as measured in amperes and not the voltage present on the wire. Think of this field as a series of closely spaced rings expanding away from the wire. The closer you get to the center, the stronger the magnetic field. Also, the greater the current, the stronger the field. A more graphic description would be like a flourecent tube lamp where light is produced all around the circumference and the closer you get to the tube, the stronger it gets. The magnetic field that is produced from this conductor can overlap onto another conductor and create an electrical current in the second conductor. Also if we introduce some iron based metal around the conductor (and hence into the field), then the field becomes concentrated around the metal. Magnetic fields have either a Northern or Southern polarity depending on which direction the current flows through the conductor. Northern polarity magnets attract Southern polarity magnets, but repel other Northern magnets. Unlike polarities attract and like polarities repel. It is this magnetic attraction and repelling relationship that makes a motor spin, depending of course on when and in which direction the electrical current is applied.

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Basic Components. There are essentially three basic parts to a motor that need to be identified in the DELCO unit. The first are the four field windings that are fastened onto the inside circumference of the starter-generator unit. These field windings have two separate wires in them, small gauge wire in the inner most and heavy 6-8 gauge wire wrapped around (over) the small wire. The small gauge wire (18 solid gauge) is the generator field coil and the heavy gauge wire is the starter motor field coil. The smaller generator field coil wire is covered with a thin coating of enamel (an insulator) which prevents the wire from shorting against adjacent turns of wire and the thinness of the coating permits the most turns to be wound in the space given. It is wound tightly and has at least 100 or more turns. The starter motor field coil uses heavy 6-8 stranded gauge wire which has itís own insulation around it (like standard wire). It is wound over the outside of the generator field coil winding with only four turns. The coil windings are usually covered in a special cloth tape called Gaffing Tape and are wound in an oval shape, intended to rest inside and under the metal ďarrowĒ shaped pieces which DELCO refers to as pole shoes. They retain the windings within the housing as well as concentrate the magnetic fields.

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The second part of the motor is the armature. The armature are the straight conductors on the outside edge of the rotating part of the motor that is encapsulated in metal. It is the armatureís function to spin inside and react to the magnetic fields created by the field coil windings. When assembled inside the starter-generator unit, the armature has a close tolerance to the metal pole shoes, leaving 1/64-1/32 inch clearance between them. The armature connects itís straight line conductors to the commutator (and brushes), which is the third part of our motor. The commutator is the series of copper segments that are electrically connected to the armatureís straight line conductors. There are two commutator segments for each armature conductor, each exactly opposite one another. It is the commutatorís copper segments that make contact with the brushes that transfer the current between the housing and the rotating armature. In general terms, we often refer to the armature and commutator as just the armature, but they really are two separate functions although they are one assembly. In this article weíll continue to call the two as the armature for simplicity.

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Principle of Operation.Now that we know the basic components of the DELCO unit, lets put it into motion. First letís operate it as a simple motor where an electric current is applied to the field coil windings which create North and South magnets around the armiture. Next a current is applied to the brushes which are making contact with one of the copper segments on the commutator. The current rushes into the segment, through the armature conductor and back out the brush on the other side. This current creates a field around the armiture cunductors and it reacts with the field coil windings (flux) by pulling (twisting) the armature towards the field coil winding of opposite polarity along with the repelling action from the adjacent field coil winding which is of like polarity. After this small amount of rotational movement of the armature, the brush breaks contact with the commutator segment and current ceases to flow through that armature conductor. With no current flowing, there is no magnetic contribution from this armature & commutator pair, however the brush has now made contact with the adjacent commutator set and the process is repeated. The result is the systematic making and breaking contact of the brushes on the commutator and the armiture spinning inside the four field coils.

Now lets consider the unit as a starter. The four brushes on the starter side commutator of the armature are lifted and held away from the commutator via a plate with four levers. Each starter brush has a small roller that makes contact with each lever on the plate. The plate (and brushes) are held back by a special tapered shaft that is connected to the starter pedal on the floor board. When the pedal is depressed, the shaft is pulled out allowing the brushes to make contact. When the brushes make contact with the commutator, a high amount of current is drawn from the battery, through the heavy gauge windings on the four field windings and to the brushes. Since the brushes are making contact with the commutator segments, the current flows through the armature where the required fields are produced. The current exits the commutator segments that are connected to the brushes that are grounded. As these currents are high (35-40 Amps), strong fields are produced thus making it a strong starter motor.

As a generator, the principle of operation is very similar, but with the currents flowing in the opposite direction. The four field windings are still energized via the ignition switch circuit. The armature is rotated by means of the running engine which is spinning and collecting the fields created inside the four field windings. The currents derived from the caught fields are carried out of the armature via the brushes, through the armature wire lead, the ammeter and ignition switch and finally to the storage battery. The DELCO 193 units use a three brush scheme connected to the commutator: One brush is connected to the armature terminal, one brush connects to ground, and the third brush connects to the fourth field coil winding. It is this third brush that is connected to a seperate plate and is moveable. It can be rotated approximately 15-20 degrees with respect to the grounded brush opposite it. Moving the third brush to be in perfect alignment with the ground brush opposite it permits maximum fields to be generated which is maximum current output (20-22 amps). Rotating the third brush causes the brushes and commutator segments to break their circuits sooner thus producing weaker fields in the coils and less output current (12-14 amps).

Tutorial on Unit Operation. To operate the unit as a starter, it must be understood that there is an intermediate set of gears inside the flywheel bell housing. These gears connect the starter to the flywheel only when the starter is engaged. They are paired together and slide on a shaft that is connected to the floor board starter pedal. This shaftís tip inside the unit is tapered which governs the lever plate that permits the starter brushes to make contact with the commutator. Finally, there is a set of brass fingers mechanically connected to one of the positive lead starter brushes. The starter unit is engaged when the following events occur in this order:

  1. The ignition switch is turned on which applies power to the starter generator via the two wires connected to the field and armature terminals. This causes the armature unit to spin slowly as it is acting (for the moment) as a motor. While in motion it produces a low pitch whirling sound which is a good audible indicator that the starter-generatorís armature isnít hung up.
  2. As the starter pedal is just slightly depressed, the brass fingers switch on the starter brush breaks contact with the armature wire terminal and thus electrically disconnects the generator. The armature continues to spin a little under momentum to permit the gears to mesh.
  3. Further depression of the starter pedal pulls the tapered shaft and permits the starter brushes to make contact with the commutator and the unit engages as a powerful motor. As the unit is turning the engine, the engine accessory shaft and water pump is also turning. In the housing between the back of the water pump and the starter-generator resides a simple roller bearing free spinning clutch.
  4. When the engine starts, both the flywheel and the accessory shaft turn considerably faster than the starter-generator was turning. The purpose of the clutches is to permit the engine to start and run at normal speed without damaging the starter-generator unit. When the flywheel clutch gears have disengaged (releasing the starter pedal), the other clutch catches and spins the unit, but now as a generator.
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Field Coil Connections.Connecting both the starter and generator field coils is critical to achieve correct unit operation. They are both separate with no direct connection between them, however the starter portion of the DELCO unit does depend on the generator coils for extra magnetic effect. Both the starter and generator field coils under each pole shoe must have the same field polarity, either North or South. If they werenít, the two-coils magnetic fields would be opposing each other and effectively canceling them. Also, each field coil must be alternating, North is always next to a South coil. Field polarities are established by which direction the current flows or by which direction the wire is wound. From a practical standpoint, the heavy gauge wire of the starter coils establish the polarities for field coils, windings #1 and #4. One heavy gauge wire is used for coil #1 and #2 and terminates at a starter brush. The same applies to coil #4 and #3 as it terminates at another starter brush. Soldered at the copper battery connection stud, each of the two heavy wires run briefly parallel before they begin wrapping around coils #1 and #4. The heavy wire wrapping clockwise (CW) around coil #1 makes it Northern polarity and the same wire wrapping counterclockwise (CCW) around coil #2 makes it Southern polarity. Therefore the generator field coils must also follow this same orientation. Ensure the generator field coils are properly connected by using the Outer or Inner leads to ensure CW or CCW orientation. Connect a well insulated wire with lug connector from the Field Terminal located above the starter brushes (closest to Field Coil #1) to generator Field Coil #1. Connect all four coils together paying attention to CW and CCW direction. Field Coil #4 lead terminates to the 3rd brush also using a lug connector.

Maintenance.Maintaining the unit is a matter of simply keeping both the inside and outside clean. First, remove power from the unit by disconnecting the battery lead. Unfasten both strap covers over the brushes and blow out any excess dirt or dust. Degrease the inside area using brake cleaner or other residue-free degreasing cleaner along with a nylon brush such as an old toothbrush. Afterwards, electrical cleaner CRC-2-56 may also be used. Remove any dirt build-up between the Commutator segments by using a tooth pick. Care should be taken when moving the armature around as not to press on the conductors between the armature and Commutators (recognizable by the fish paper between them). Inspect the three generator brushes for any dirt build up in their holders. They should easily slide up and down and be held in place by the tension of their spring. Greasing the front and rear bearings should be done if itís known that they havenít been changed to sealed bearing versions. Also check that the third brush is free by moving the metal tab exposed in the rear generator brush slot. Fasten strap covers, reconnect battery and verify the unit operates properly.

Repair and Overhaul.Repairing the DELCO 193 starter-generator usually occurs when it no longer operates properly, either as a starter or as a generator. Assuming the maintenance tips mentioned above have been followed without success and all other posssible causes have been eliminated, then proceed to remove the unit from the enigine. This involves removing the water pump, water pipe, and accessory shaft as well. On a bench, preferably resting vertically on top of wooden blocks, remove the back clutch assembly, starter gear & spacer, and the four long screws holding the back generator brush housing (the back portion of the DELCO unit). Unscrew the terminals for the two wires to the brushes; the adjustable third brush from the #4 field coil and the positive voltage lead from the armature terminal. It is suggested that these wires be marked with tags. Remove the rear housing taking care not to let the brushes fly freely from their holders. Carbon brushes are fragile and can break easily. Also note any extra washers that may come loose around the rear bearing retainer. Carefully lift out and remove the armature assembly from the DELCO unit while anticipating that the four spring-loaded starter brushes will snap inward when they fall off the their commutator. Inspect the areas around the main housing and look for loose, worn or frayed wiring around the field coil winding under each of the pole shoes.

Preferably using a digital multimeter, measure the total resistance of the four field coils. The generator field coils each have a resistance of approximately 0.4 ohms, therefore the total resistance between the field terminal and the wire that was removed from the adjustable third brush should be about 1.6 ohms. Also check for continuity between the field coils and ground (the housing) which should be infinite i.e. no shorts to ground. Another easy inspection is to apply six volts across the field coils (positive to the field terminal and negative to the 3rd brush wire) and use a compass to verify magnetic polarity. The next electrical measurement involves checking the armature on a magnetic flux analyzer commonly referred by rebuilding shops as a Growler. Check with local service shops who will usually perform this inspection at little or no cost. If the armature requires rewinding, this must be performed by a professional and is usually rather expensive, ranging from $300-$500. Without a properly functioning armature, the entire DELCO unit will not work and the armature must be repaired/rewound or replaced.

Overhauling the DELCO unit involves swapping out the two bearings for sealed versions and if necessary rewinding either or both of the field coil windings. The wire in the generator field coils is coated with an enamel and may become brittle with age and heat, but usually holds up and should only be rewound if absolutly required. Covering a simple scrape with shrink tubing should suffice. The starter field coils however are cloth covered heavy gauge wire and the cloth insulation may very well have dissintegrated and is likely to create shorts against itself or worse, the housing. Rewinding these can be perfomed by 1) removing the slotted screws holding all four pole shoes (mark which pole shoe and direction belongs to each field winding), 2) removing the four slotted screws holding the starter brush plate, 3) pressing the copper battery terminal through the housing, and 4) finally slide out the coils and starter brush assembly from the housing. The cloth tape an be cut away from the field windings revealing both sets of coils. The heavy gauge wire can be replaced using 8 gauge stranded THHN Gas & Oil rated house wire. Using a stiffer wire is preferred in order to maintain the oval shape. Each pass of the wire must be tight against each other and in pairs as shown in the cross section diagram. Otherwise the winding will not fit properly under the pole shoe. Also note the proper direction of each winding. Cover with cloth Gaffing tape such as 3M 6910. Do not use Duct Tape as its adhesive will drip into the armature when the unit becomes hot. Verify polarity using the compass method.

Cosmetically the DELCO unit can be cleaned and painted or powder coated prior to reassembly. Refit the starter brush plate to the housing and secure each of the coils with the pole shoes. Pole shoes must be absolutely tight and thread locker may be used. Reinsert the armatue and verify proper clearance between it and the pole shoes (sanding or light grinding of the pole shoes may be required). Secure the rear cover and check for end backlash (.020-.030). Seat the generator brushes into their holders and connect the two wires to the brushes, Field Coil #4 to 3rd brush and Armature wire to the positive brush. Insert the starterís tapered shaft into the unit to lift the starter brushes, apply six volts to the both armature and field terminals and ground and verify the unit motors at low RPM.

Troubleshooting the DELCO 193 Starter-Generator

Unit does not spin when ignition is on. Verify power to field & armiture terminals, check generator brushes and generator coils. Armature may also be bad.
Starter works but not generator. Verify power to field & armiture terminals, check brushes, check generator coils. Check if current is present on Armature Terminal. Check wiring through ammeter circuit.
Unit spins occasionally when ignition is on. Lubricate armature bearings, starter drive gears, and starter shaft.
Unit spins but starter does not work. Check four starter brushes. Ensure they are making contact to commutator when pedal is fully depressed.
Armature frozen (wonít spin). Check bearings examine for any debris between armature and pole shoes.
This page last updated on
30 October 2006