Rich Mozzetta PDF compiled by Dave Zuberer Chevrolet Generator Rebuild and Restoration I had 2 old Chevy generators and I used parts from both to create a new one for a 1960 Corvette project. Both generators had the correct armatures with the extended shafts to drive the Tachometer Drive units. These same armatures were used to drive Power Steering pumps on Chevy and other GM passenger cars of the era. However, the Corvette applications used different end frames and front frames. Corvette end frames were approximately 1/4" shorter as measured between the center of the armature shaft and mount points. Front frames for passenger cars had reinforcing ribs along the perimeter whereas Corvette shorter frames did not. The passenger car frames will work for Corvette but will appear slightly different when installed. See the addendum at the end of this document for more information about the differences. Below is a procedure I use to restore and rebuild my generators. Below is what I started with after disassembly. To disassemble, remove the 2 long bolts (circled) holding the frames and case together. The frames should pull off the bearings. You may need to free them up with penetrant to get them to release. Both were tired from age but tested fair when "motored". To do a basic test of a generator, that is, to motor it, connect a battery Positive (+) lead to the "A"(armature) terminal, battery Negative (-) to the "F" (field) terminal, and battery Negative (-) to the generator case. This will run it as a motor and it s just a basic test to see if there's life, and to listen to the bearings and any strange sounds before rebuild. Both armatures had bad bearings and needed replacement. I could hear them singing when I motored them. The original factory generators used open ball bearings so that they could be oiled periodically through the "Gits" caps. Gits was the manufacturer of those little spring-loaded oil caps. The bearing number for both front and rear is 6203J. If sealed bearings are used in a rebuild, they cannot be oiled through the caps. I use the original open type for future oiling, NAPA part# BRG6203J. 1
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A puller is used to remove the commutator end bearing. I then use my lathe to shave the commutator and clean all contacts with 1000-grit sandpaper while it's rotating. I also clean the shaft bearing surface and install a new bearing. It should be a slip fit over the shaft with slight resistance. After the lathe work I clean each space between commutator contacts to remove any traces of copper shavings between them. This step is tedious but very important! 3
Next I use my Growler to test the armature after the commutator clean-up. This tests for opens or shorts in the windings and shorts to the armature case. The hack saw blade is part of the test. If it vibrates as the armature is manually turned on its axis it has found a fault in the windings. This one tested fine. Other tests include commutator point-to-point opens and shorts to case/ground tests. Those can be done with a test meter as well. This growler has a built it test light so I use that. Commutator to case/ground shorts test. One lead to case, then other test lead to each contact around the commutator. 4
Below is the commutator windings opens test. Both test leads on each adjacent contact, leapfrogging over each one to test for opens in each winding pair. Tedious but important! I remove the field coils to clean the case in solvent and to prepare it for media blasting. I use a large slotted bit and an impact gun to remove the screws. This set had a broken wire at the terminal when I removed it which I soldered later. The insulator was cracked and allowed the terminal to turn when removing it. I repaired the insulator as well. 5
Cracked terminal insulator 6
Finally, I clean and media blast all of the parts and repaint them. The case is semi-flat black, the cast iron end frame is Gloss black, and the front frame is unpainted casting. The pulley is semi-gloss black. Alignment slot Alignment pin 7
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Note that the pulley for the Corvette is 3 5/8" diameter and is spaced above the fan 1/4". This is to line up the belt to accommodate the added thickness of the front motor mount on the early Corvettes up to 1962. ¼ Now assembly begins. The bearing in the front frame has a special felt washer and cover plate. Note the cover plate must be installed as shown. When oil is applied to the Gits cap, it flows down into the felt washer through the detent in the cover plate. The bearing is then pushed into the housing and then the gasket and keeper plate is installed Oil the felt washer 9
Felt washer in housing 10
I reinstall the field coils into the case and use a touch of blue thread locker on the screws. Then the F & A terminal studs are installed ensuring correct alignment to the case. The F stud must be insulated, the A stud is case ground. Do not over tighten them or you can crack the insulators as was done on this F insulator in the past. My trick of using super glue and baking soda to fill the crack fixed this one. Insulator Crack repair Field stud A stud reattached 11
I installed new brushes (Napa ECH423) and locked them into the rear of their holders to install the armature into the case. Once the armature is in position the brushes are released to contact the commutator. I then install the end frame onto the bearing. A little oil on the frame bearing surface eases installation. Install the 2 long bolts to hold the assembly together. The frames and case have alignment pin/slots to ensure correct positioning (see earlier photos of case). Note the spacer bushing at the front shaft before the pulley is installed. This aligns the bearing to the shaft and locks it in to prevent end play. The pulley requires a key to be installed in the shaft keyway. Don't forget that. I use a band clamp to hold the pulley when I install the lock washer and shaft nut and tighten using a 1/2" drive breaker bar and a 15/16" 6-point socket. 12
I then motor the generator and check its operation. This one is running much smoother and quieter than before. New bearings, commutator cleaning and general restoration has made it run and look new again. I do not own a load tester so I'll have to wait until it's installed on the car for proper operation under load but all of the rebuild work and tests have given me confidence it should work properly. I then install the Tach-Drive unit to the end frame. Note the Red lead is actually connected to the battery "-" terminal in the motor test. Here is the completed unit on the shelf ready for installation at a later time. 13
Addendum Below is a reprint showing the differences of Generators used on Passenger cars and Corvettes. Unfortunately it has no Author named. I would like to give credit to that person but no reference has ever been found. C1 Correct Generator: The 55-59 pass car PS generators, 1102114 and 1102115, use the same case and rear splined armature as the Corvette tach-drive generators but the end frames are different. The difference is in the distance between the centerline of the armature and the centerline of the rubber bushing mounting bosses. The distance is shorter on the Corvette than the PS gen. This is accomplished by using different front and rear end frames. The Corvette front end frame is aluminum and is part #1933109. The PS generator 1102115, which is the most common PS generator seen, uses the aluminum front frame # 1941168. Visually, the difference is that the 109 frame doesn't have the radial reinforcing ribs and the 168 frame does. The PS rear end frame is cast and the part number is #1938726 and has a noticeable distance between the lower PS pump/tach drive mounting hole and the lower rubber bushing mounting hole than the Corvette rear end frame which is #1934131and is also cast. The PS generator can be fitted with the tach drive and used on the corvette, but it will stand slightly taller on the mount and, of course, will not have the correct part number on the tag. There were other PS generators with solid mounting instead of rubber mounting, and they could be used but they are not correct as the Corvette 1102043 generator was only rubber mounted. 14
Here are some examples of incorrect generators. This one I call a "mongrel". It has the correct "End Frame", but the incorrect Front frame (ribbed). Notice in the 4th photo that the horizontal alignment is off. This generator will be pointing "uphill" when mounted. For 1958 to 1962 Corvettes, it has the wrong 3 5/8" pulley mounted. It should have approx. 1/4" space between the back of the pulley and the face of the fan. 15
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This is a picture of a Passenger car generator with a Power Steering unit installed. It has the same extended shaft on the armature to drive the pump. Many Corvette Tach Drive Generators start life as one of these, but will have the incorrect frames and pulley. It will work, but it won't be the correct type. Similar type showing drive shaft extension and end frame. 17