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Ideas for removing a generator rotor?

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  • Ideas for removing a generator rotor?

    Have a small navy genset, 110V 400hz, which I need to disassemble for some crankshaft work. It is a PU-278, from an AN/TRC-27 microwave link.

    Motor is a Briggs 6B with a generator bolted on the PTO side, and rotor directly on the crankshaft PTO stub. I need to pull the crankshaft, but to do that I need to pull the PTO side cover.
    To do that I need to pull the generator (alternator).
    And to do that, I need to remove it's rotor from the crankshaft.

    This is NOT going well, there is hardly anything to grab. And the rotor is stuck on there well, probably has been there for 50 years.

    Here are two views of the rotor. No puller I have will fit into the slots that are open, they will barely pass a 5/16 inch rod. The rotor seems to be a taper fit, with the capscrew to cinch it up. I have already hit it with PBlaster, and have screwed in a capscrew and tapped it smartly, similar to a flywheel remover. No soap.

    I am contemplating making puller jaws to reach in, but I am aware that they will be relatively thin and weak. After going to the trouble of making them, I may not get much but bent puller jaws.

    Not only that, but there are SEVEN slots, so NEITHER a 3 jaw NOR a 2 jaw puller fits with a straight pull.

    So I am looking for ideas that I have not thought of.

    Naturally, the rotor is powerfully magnetized, and would not let loose of the shaft quite like a flywheel, so the tapping MIGHT not work as expected, but I would think I could tell if it loosened. Wedges behind would be good, but no place to put them, as there is no access to the back side of the rotor.

    I can't heat it enough to make a difference, both because it might affect the magnetic strength, and because the stator coils are right there. The rotor is massive enough to require some serious heating to get it hot without heating the shaft just as much.

    Drilling and tapping holes for a shop-made capscrew type puller is good, but the rotor is a magnet, and so is hardened.... I probably wouldn't get that done without great risk of messing it up, and maybe breaking a tap in it.

    The coil assembly is bolted to the PTO cover, and neither is coming off until the rotor is loose.

    And, the rotor and stator need to come off together, as the rotor needs a "keeper". But that is no problem, since I can't do anything with the stator until the rotor is loose in any case.

    On these 6B motors, there is no other way into the crankcase other than the PTO cover. So I can't pull the flywheel and slide out the whole crank. The conrod would have to come off first, but it can't be reached.

    Any good ideas I have not thought of?

    BTW, no manuals available, so no help there.

    Keep eye on ball.
    Hashim Khan

  • #2
    Can you use that old trick for removing bushings from a blind hole?Plug the hole with grease and compress it with a close fitting punch.I mean whack the punch with a hammer.Most generator rotors I have seen do use a taper.


    • #3
      Originally posted by paulx
      Can you use that old trick for removing bushings from a blind hole?Plug the hole with grease and compress it with a close fitting punch.I mean whack the punch with a hammer.Most generator rotors I have seen do use a taper.

      Not sure how that would work.... there isn't a 'backside" where the grease could apply pressure.

      Am I missing something?

      Keep eye on ball.
      Hashim Khan


      • #4
        J Tiers, As a long time mechanic, your pictures tell me that drilling & tapping would be my first choice. From what I could see in pics the outer part looks thick enough to support a three or four bolt hook up. I would try a tiny little drill bit to start, that should give a good indication if the piece is machinable. If it wont drill it wont tap either. If it drills I say go for it.JIM


        • #5
          I guess I am missing something.The grease would just pump out the other side?


          • #6
            J Tiers,

            I bought a factory service puller for a rotor similar to yours, a 1/2" plate disc who's diameter was larger than the slots, with holes directly over the slots, the puller arms were piece steel with 1/2"-13 B-7 allthread for rods. This also was for a rotor with an odd number of slots. A center drive bolt was a piece of 5/8-18 B-7 allthread. Very crude looking, but worked great.

            Last edited by platypus2020; 08-11-2007, 01:03 PM.


            • #7
              J. Tiers,

              Maybe I'm not understanding the problem...

              If you're saying the rotor is stuck to the shaft then perhaps you can apply a vibration by using an air hammer (or similar) while saturating the area with the PBlaster. Hopefully the vibration will help "suck" in the PBlaster so the rotor will loosen.


              • #8
                THAT is a good idea.......... Thank you.

                Saves drilling, but same plan. I like it.

                So obvious, but I got fixated on a "puller".........

                Keep eye on ball.
                Hashim Khan


                • #9
                  When I had a small engine shop the trick to get flywheels off was to hold up one side of the flywheel with my hand and wack the end of the crank with a brass or lead hammer a very sharp blow. Unless the key was sheared it came off with the first blow. If you could hook something in one of the slots and pull hard while someone wacks the end of the crank with a piece of brass stuck in where the bolt was it may pop right off.

                  If it is a Briggs look up the fllywheel in a parts manual and it will tell if it is a tapered shaft.

                  I still have many of my old manuals and if you can tell me the engine model number and serial number and code number I may be able to tell if it is tapered.
                  It's only ink and paper


                  • #10
                    I had a small generator with the same problem. I hooked up a DC supply and ran a few amps thru the coils. That warmed it up and I got it off with no problem.


                    • #11
                      I was thinking along the lines of Platypus, a plate with holes drilled as appropriate for the spacing. You said 5/16" would barely fit, so that suggested 5/16 carriage bolts with the heads ground off most of the way to provide a hook with what's left. The roughly oblong holes would hopefully allow you to get the hook down, then rotated to grip. Nuts on both sides of the puller plate make sure you can hold orientation of the hooks. Then jack and whack away.
                      "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill


                      • #12
                        Rotor Removal

                        Check carefully in the mounting hole. At least some types of rotor have a set of puller (push off?) threads located inside the hole. Under casual inspection they look just like the mounting bolt threads in the end of the crankshaft but they are actually a size larger. I fought a chipper rotor for hours before I discovered this little detail. Have since discovered that several types of rotor have this detail. Your rotor may not have this feature but be sure to check it carefully. If it does it will prevent a lot of gray hair. You will need a suitable length of push pin inside the hole for the puller bolt to push against.


                        • #13
                          It is a 6BFB 903539 ser 144793.

                          Made for Navy via Raytheon & Hol-Gar


                          (no threads, though)

                          Keep eye on ball.
                          Hashim Khan


                          • #14
                            When you've tried the less extreme methods and they haven't had the desired effect:

                            Find a bolt that just fits into the rotor's bore. Weld a corresponding nut onto the rotor, when it's hot, screw the bolt against the end of the crankshaft.

                            Good luck,

                            All of the gear, no idea...


                            • #15
                              I suppose this is the same as screwing in a capscrew and smacking it, but it may give a little more 'punch'- machine up a solid plug that fits well into the recess, and smack that. I would be rounding off the hammer end slightly so the pressure pulse from the smack is roughly centered with the shaft's axis.

                              In this same vein, you could machine that plug for a slight press fit to the recess, and trap some kroil or your choice of penetrant in the cavity. I would probably upend it and fill the threaded hole and the recess, then squeeze the plug in best as possible, expelling all air at the same time. Give that a good whack or two. You might at least have some luck getting the penetrant past the end of the shaft.

                              Obviously there could be a high pressure spray escaping from the area, so it would be prudent to wrap a catch cloth around it, and wear eye protection.
                              I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-