Delco Remy Starter Generators – How They Work and Testing

[29 Chev]

Two short pieces of 2 x 4 can be used so the front plate rests on them and the unit can be stood upright.

With the two brush arms, springs and field wires in their approximate place the brush arms can be held back and the brushes installed. A new set of brushes was installed as one of the wires on an old brush had broken away from the actual brush.

 

[29 Chev]

The brush screws were then installed connecting the terminal ends of the field coils to the appropriate screw. I will note that the F and A posts got installed in the housing along with the appropriate insulators when the field coils were installed earlier. Unfortunately the A post left the wire oriented in the wrong position so that the two long bolts that hold the front and rear plates to the housing could slide through inside the housing.

Eventually I got the post rotated and the red Shunt Field wire oriented so that there was room for the two bolts.

Then the end plate got set in place and the two bolts could now be installed.

 

[29 Chev]

Both bolts got threaded in loose and after verifying that the two plates were oriented properly and the plates were sitting flat on the housing the bolts got tightened.

The bolts did not extend flush with the threads in the front plate but they threaded in several turns. The nuts were placed on the two posts.

 

[29 Chev]

The unit was now ready for a test and when tested it worked ok as a starter but would only produce about 0.5 volts as a generator. It turned out the insulation around the armature windings was not in the best condition so I ended up installing a new armature. The part number on the box was 6101-0013 for my unit. Other units may be a different length or they may rotate in the opposite direction so this part number will probably not fit your unit if it is a different Delco Remy number.

The first thing I did when the new armature arrived was compare the new Armature with the old one to make sure they were the same length, diameter, etc. It looked to be correct and so it got installed and then the unit worked as a generator and a starter.

 

[29 Chev]

It took me a few times of removing the starter generator on my tractor and installing this unit to determine that the armature was the problem as to why it would not work as a generator. During this process I also noticed that when I installed the repaired unit the belt did not slip while starting the engine the way the unit on the tractor did. I did a close visual inspection and found that the pulley on my unit was badly worn and the belt was sitting low in it and not gripping the sides properly the way it did when the repaired unit was installed with its pulley. It is hard to believe that rubber can wear steel but here is a picture of the worn pulley and how the belt sat in it.

Here is how the belt sat in the repaired unit’s pulley – as you can see it sits at the top of the V instead of down in as above. I ended up building up the worn pulley with weld and then turning it back down in the lathe so the V was narrow and smooth. This was a bit of work and if someone encounters a worn pulley it may be easier to just source a new pulley the correct diameter and modifying the center to make it fit on the shaft and woodruff key.

 

[29 Chev]

Some Miscellaneous Information

During the repair process I measured the resistance of the Main Field Coil and the Shunt Field coil when not connected to anything – here are the readings I got on this unit - your unit may very.
Shunt Field Coil - brush terminal to field post – Approximately 8 ohms resistance
Main Field Coil – brush terminal to armature post – Approximately 0.1 ohms resistance

When checking for shorts in the Armature I found that I was getting a reading of about 75 - 110 ohms when I measured between the Armature shaft and the segments on the commutator. Initially I thought this was acceptable since it was not what appeared to be a direct short and the unit appeared to function fine as a starter. I have since learned that this reading is not acceptable and there should be infinite resistance between the commutator segments and the Armature shaft.

I was curious as to how fast the starter generator armature turns at idle, when it starts to output useful power and at wide open throttle. I measured the diameter of the starter generator pulley (2-1/4") and the engine pulley (7") on a Bolens 1053 which uses the same engine and tarter generator as a Bolens 1050. This works out to a ratio of approximately 3.11 : 1. According to my math this indicates the starter generator on my Bolens 1053 rotates a little bit more than three times for every revolution of the engine. Did some calculations and here are the results which I found interesting as a starter generator turns at a speed I consider to be very fast. At 900 RPM engine speed (idle) the starter generator is rotating at approximately 2799 RPM. At 1100 RPM engine speed (speed where S/G begins to show charge on the ammeter) the starter generator is rotating at approximately 3578 RPM. At 3000 RPM engine speed the starter generator is rotating at approximately 9330 RPM. I will point out that the starter generator pulley is quite small in diameter in comparison to the engine pulley and there is not a lot of belt surface area engaged with the starter generator pulley. This is why it is important to periodically check the belt tension so that the belt does not slip in the starter generator pulley as this can easily start the belt and the pulley to begin to wear.

One other thing I will share before we move on to testing a starter generator is that I once talked to person who had worked for about 25 years as a small engine tech. He had encountered a starter generator that would work but did not seem to have much torque to turn an engine over. He tested each component using the service manual and everything checked out fine so he ended up replacing the unit with another one to get his customer fixed up. The old unit sat on a shelf for a few years and he ended up talking to an elderly electric motor repair person and it came up in conversation. He ended up taking the unit to the gentleman and the gentleman took it apart. The gentleman studied the components for a minute and told the repair tech the unit had the incorrect armature installed in it. A new armature was ordered and installed and the tech told me that the unit then worked fine with adequate torque. I only mention this since most of these units are at least now 50 years old since they were new and if somebody tried to make one out of two a similar situation could arise.

Some people suggest that to test the starter generator it be ran as a motor by connecting the unit to a 12 volt battery using a set of booster cables – the negative cable to the body of the starter generator and the positive cable to the A (armature) terminal. The armature should spin up and then while the armature is turning remove the positive cable from the A (armature) terminal and connect it to the F (field) terminal and observe if the unit stops quickly since doing this will result in the Shunt Field Coil acting as an electromagnetic brake on the armature. While this test verifies that the unit works as a starter and the integrity of the Shunt Field Coil and its wiring it still does not guarantee that the unit will work as a generator. I did perform this test on my unit with the bad armature and it appeared to pass the test as the armature stopped quickly when the F (field) terminal was energized but still would not produce electricity due to the partially shorted armature windings.

 

[29 Chev]

Testing of the Starter Generator and Regulator

Hopefully by now the reader has a good understanding of how the starter generator, regulator and other components work together to make the starter generator work as a starter and as a generator.

Starting Problems
Let us first look at a problem where the starter generator will not crank the engine over on a garden tractor application.
Here are some things to check

1. Make sure that the engine rotates freely and is not seized and that the belt between the engine and the starter generator is tensioned properly and not slipping. The belt may be removed temporarily to make sure that the starter generator rotates freely without any load on it when the starter switch is activated. The amount of current and rpm can also be measured during a no load test and compared with the specifications given in the IMG-186 test specifications pages to see if the unit is drawing too much current and turning at the proper rpms.

2. Make sure the battery is good and fully charged – a discharged battery may not provide adequate current to power the starter generator and crank the engine.

3. Inspect all wiring connections, terminals, wires and cables to make sure they are all clean and tight. Any internal resistance of more than 0.1 ohms at any connection point in a 12 volt circuit can be enough to starve the starter generator for current.

4. A bad starter switch or solenoid may not be making proper contact internally to allow proper current flow to the starter generator.

5. A set of booster cables can be temporarily connected to the positive and negative battery terminals and the starter generator case (to the negative battery terminal) and the A (armature) terminal of the starter generator (to the positive battery terminal). If the starter generator still does not turn the engine over then odds are there is a problem inside the starter generator. I would suggest that you refer to the attached Delco Remy IMG-150 Service Bulletin for the proper tests procedures of the internal components.

 

[29 Chev]

Charging Problems
Charging problems can be broken down into two scenarios – Overcharging (too much output) or Undercharging (not enough output).

Overcharging- Voltage or Current Output Too High
If the starter generator works ok as a starting motor but overcharges the battery causing it to boil or light bulbs burn out after a very short time period here are a few things you can check.

1. Connect the positive lead of a direct current voltmeter to the A (armature) terminal of the starter generator and the negative lead of the voltmeter to a ground point. Temporarily remove the wire that is connected to the F (field) terminal at the starter generator. Start and operate the engine at about 1500 rpm and observe if there is any voltage reading at the voltmeter. If a voltage reading is obtained there is a problem within the starter generator - removing the wire to the Field terminal should make sure the Field terminal is not grounded and as a result no voltage should be produced.

2. If no voltage reading is obtained in the test above check the wire that connects to the F (field) terminal of the starter generator for a partial or full short to ground. There may also be a problem inside the regulator where the regulator arm contacts may be stuck together or there may be a partial or full short from the F (field) terminal of the regulator to the regulator body. If there is no voltage produced with the F (field) wire disconnected at the starter generator but there is an overcharging issue then something in the regulator wiring circuit or inside the regulator is keeping the F (field) terminal of the starter generator connected to a ground point for a longer period of time than it should be resulting in the starter generator producing more current or voltage than it should.

Undercharging – Voltage or Current Output Too Low
If the starter generator works ok as a starting motor but the battery is not being charged here are a few things you can check.

1. Check drive belt tension. Odds are that if the starter generator cranks the engine the belt tension is adequate but the belt could be loose enough to slip as the engine, starter generator and belt heat up.

2. Inspect the wiring checking that all connections are clean and tight with a resistance reading of 0.1 ohms or less.

3. Connect the positive lead of a direct current voltmeter to the A (armature) terminal of the starter generator and the negative lead to a ground point. Use a jumper wire to temporarily connect the F (field) terminal of the starter generator to a ground point. Start and run the engine at about 1500 rpm – if a voltage reading of around 12 – 14 volts is obtained the starter generator is capable of producing power and there is a problem somewhere in the F (field) wire circuit. Either the field wire has an open between the starter generator F (Field) terminal and the F (Field) terminal of the regulator or there is a problem inside the regulator. The cutout contacts may not be closing or the regulator contacts may be open or either the cutout and or the regulator contacts may be dirty or pitted creating resistance so that the F (Field) terminal on the starter generator cannot complete the circuit connection to ground. The cover of the regulator can be removed and the cutout contacts and regulator contacts observed to see if they are open or closed. I once encountered a regulator that would work properly sometimes and other times would not. I happened to be troubleshooting it near dusk with the cover off and with the lack of full daylight noticed arcing at a soldered connection on the contact relay coil. I resoldered the connection and the regulator worked properly again.

4. If no or a very low voltage reading was observed with the engine running at 1500 rpm and the F (field) terminal of the starter generator connected directly to ground there is a problem inside the starter generator. The unit will have to be taken apart and the components tested to see where the fault lies. As I stated earlier the unit I worked on would crank the engine over fine but had no voltage output and I eventually determined that the insulation on the armature windings was defective resulting in a partial short to ground between the commutator segments and the armature shaft.

 

[29 Chev]

This concludes the testing procedures I can offer for the starter generator and regulator. It is my hope that the information in this thread is useful to anyone with a Delco Remy starter generator problem.
I have attached a numerical list of Delco Remy starter generators that shows some of the specifications and the direction of rotation for each unit. To my knowledge Delco Remy starter generators were usually 12 volt - there is one 24 volt part number listed in the Test Specifications document.
Also attached is a parts breakdown for the Delco Remy starter generators that were used on Bolens tractors, a quick troubleshooting guide for various problems and the Delco Remy service bulletin for the 2 post combination voltage and current regulator.
For those wanting a pdf copy of the information I have posted in this thread there is a copy attached.

The following Delco Remy publications contain information that may help when testing or troubleshooting a Delco Remy starter generator
IMG-150 – Delco Remy Motor Generator Service Bulletin - pdf copy in first post of this thread
1MG-186 – Delco Remy Service Test Specifications - pdf copy attached
DR7275 – Delco Remy Motor Generator Field Service Bulletin - pdf copy attached
1R111 - Delco Remy Regulator Service Bulletin - pdf copy attached