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Knocking Generator

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  • Knocking Generator

    I thought my engine had a bearing knock but it stopped when the fan belt was taken off. The water pump had a lot of end play and would move forward and back on acceleration and deceleration. Replaced the pump and the noise is still there. With a wood stick to the ear, the noise was loudest at the generator. It makes a loud knocking, especially at low rpm idle. It has about 0.035" end play in the shaft but it seems tight and easily turns by hand with no resistance. Seems like a bad bearing would make a whining sound that changes pitch with an increase or decrease in rpm but this one doesn't. I have never heard a knock come from a generator. Before I take it apart, is there any test I could do first that might confirm why it is so noisy? Anyone ever have a standard 3-brush generator that knocked?


  • #2
    With the belt off jump the terminals and see if it knocks while it is motoring. I had a noisy one but not really a knock. A little ATF in the oiler holes took care of it.
    I'm sure Tom W will be along soon
    2 1930 Tudors

    Henry Ford said
    "It's all nuts and bolts"

    Mitch's Auto Service ctr


    • #3
      When I checked the shaft with the generator in the car and the belt loose, other than the end play, it seemed to be tight. After starting this thread, I rechecked it on the bench this afternoon and, indeed, found the shaft to be loose. There is more than a little movement when I grab the pulley and move it perpendicularly to the generator body, suggesting that the bearing is bad. Hopefully, the shaft and everything else is ok.



      • #4
        Well, this is sure timely, as I was just getting ready to post about the same thing. This morning I took apart a generator to restore, but then had to take apart a second one, in hopes enough good parts from two will make one good generator. The shaft moved in and out a 1/4", and it also moved about 1/8" radially. With minor bearing spinning on the shaft, I can correct it by knurling the worn area with my lathe, but this shaft is way beyond knurling. It even wiped out the rear snap ring groove. Someday, when I have spare time, I will weld it and turn it to size, and put the lock ring groove back in.

        It's a shame the front bearing wasn't kept oiled, as the commutator is in mint condition. This is why I install a sealed front bearing on generators. Of course before doing any work on this armature, I'll have to test it first on the growler, to see if it's even worth saving.

        Armature Worn 1.JPGArmature Worn 2.JPG


        • #5
          Damn, isn't that the way it always goes Tom, you find great commutator and the shaft is dead?
          VFF Recruiter

          "We do not stop playing because we grow old;
          We grow old because we stop playing ...
          NEVER Be The First To Get Old!" Pilfered from the MAFC SA Newsletter


          "Why so Serious?"


          • #6
            Yes, now I have 3 armatures with mint commutators, but shorted windings, and a ground up shaft.


            • #7
              Saturday, our club had a tour, and I was able to have a member who repairs Model A's ride along for one leg. I've had what seemed more like a rattle than a knock, and from my description, several people thought I had wear in the block where the camshaft goes thru. My mechanic friend had me play with the advance and retard while driving and didn't think I had a camshaft issue. He thought something attached to the engine, like a pulley, or the front generator bearing was causing the noise. Today, I removed the belt and could feel play in the front generator bearing when moving the pulley up and down. It also made a noise. I didn't feel front to back play. I started the engine with no belt, and didn't hear the noise, which usually started around 30 mph. It would go away when accelerating, and was loudest cruising. But it seems to be gone, without the belt. I had to leave for the day, so I still have more to check. I do have a spare generator, so I will report back, but it may be several days.


              • JDupuis
                JDupuis commented
                Editing a comment
                Please keep us posted. Jeff

              • Fred S
                Fred S commented
                Editing a comment
                I put on a different generator, and I'm still hearing the rattling noise.

            • #8
              I took the generator apart today and found the bearing had spun on the shaft. It looks much like the photo Tom posted although not as worn. My worn area is 0.014" smaller than the original size of the shaft near the outer snap ring groove. The bearing does not seem to be worn and fits snugly on the outer unworn part of the shaft but probably should be changed just in case.

              Researching this problem, I read that a pointed chisel can be used to raise some burrs on the shaft to provide enough friction to hold the bearing in place. Also that Locktite can be used to hold it. However, would the 0.014" difference be too much to do that?

              I would appreciate any ideas on a fix to hold the bearing in place or telling me bad news that the shaft is too far gone to save it. Hate to lose a perfectly good working generator.



              • #9
                Use a sharp center punch to make several punch marks all around the worn area. Then use a Loctite product that fills in the space for worn shafts under bearings. If you can't find the Loctite product, then I'd use a thin coat of JB Weld, and wipe off the excess as soon as the bearing is tapped into place. I use a short piece of tubing to tap the bearing on, so you are only pressing on the inner race. Don't hammer on the outer race.

                Don't forget the inner thin retainer plate before installing the bearing, and the notch in the plate goes up to clear the oil cap rivet.
                Last edited by Tom Wesenberg; 05-17-2018, 02:15 PM.


                • #10
                  Thanks for the advice, Tom. Good to know the shaft is salvageable and I can get the generator back into operation. I'll place an order for a new bearing and other shaft parts today.

                  Sometime the gods look upon us favorably. When I bought the car several years ago, it came with a used generator in the trunk.....owner didn't know if it was good or bad. I tested it and it motored with no problem. Put it on the car and it works fine. So, the car is now back on the road and the generator with the bad spun bearing can now be used as a backup after I repair it.