View Full Version : Ideas for removing a generator rotor?

J Tiers
08-11-2007, 10:48 AM
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.

08-11-2007, 11:50 AM
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.

J Tiers
08-11-2007, 11:53 AM
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?

08-11-2007, 11:55 AM
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

08-11-2007, 12:07 PM
I guess I am missing something.The grease would just pump out the other side?

08-11-2007, 12:54 PM
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.


Mike Burdick
08-11-2007, 01:04 PM
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.

J Tiers
08-11-2007, 01:06 PM
THAT is a good idea.......... Thank you.

Saves drilling, but same plan. I like it.

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

08-11-2007, 01:52 PM
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.

Mike W
08-11-2007, 02:09 PM
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.

08-11-2007, 02:23 PM
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.

08-11-2007, 02:50 PM
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.

J Tiers
08-11-2007, 04:04 PM
It is a 6BFB 903539 ser 144793.

Made for Navy via Raytheon & Hol-Gar


(no threads, though)

Ian B
08-11-2007, 04:10 PM
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,


08-11-2007, 05:05 PM
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.

08-11-2007, 05:45 PM
Assuming you have repeatedly tapped around the perimeter with a hammer, then held the rotor whist someone else smacks the center bolt sharply, make a quickie puller.

Use a piece of flat big enough to bridge 2 slots. Take some longish bolts (5/16" is all that will fit?) and grind a slot that will fit the rotor near the end - a little rake wouldn't hurt OR just grind away half the head of a 1/4-20 bolt. Drill the bar for the bolts (sloppy is fine) and drill and tap for the center bolt. Hold the puller 'arms' firmly in place with electrical tape. Put tension on the center bolt and whack it with a hammer while holding onto (or suspending by) the puller.

08-11-2007, 05:55 PM
Before you break it loose, its a good idea to slip some zipties in between the stator and rotor so it doesn't drop down and damage the windings as you pull it out. "ask me howI know this":eek: . Good luck.


George Hodge
08-11-2007, 11:02 PM
I bought a similar genset with the same problem.Rod broken,they couldn't figure how to seperate things.Screw that center bolt back in and leave any washers off,so that the head is not touching the armature.Use about a 3 pound hammer and whack the bolt head a good one.Mine came apart the first smack. Cleaned the hole in the block where the rod broke out,covered the hole with masking tape and filled the hole with J B Weld. New rod and gasket and I'm in business.

J Tiers
08-11-2007, 11:25 PM
That's what I've been doing. I've been hitting it pretty good licks but didn't want to hit it THAT hard in case I messed up the bearings, or cracked the case.

Good to know yours came apart well that way. Shows I'm on the right track.

This one had only one problem I can find aside from a bum magneto coil (3 leg) and a cab that needs a rebuild badly. I found new/used coils for it, but have not got the rebuild kit yet. I generally wait on expensive items until I am pretty sure nothing else will end up being a "stopper".

The one problem is that the threaded part of the crankshaft that takes the flywheel nut is broken off. A stud was put in to take a nut, but they threaded it LH so that when you try to torque it down, the stud comes out of the crankshaft.

I wanted to get the crankshaft out so I could see what I can do about that.

Either fix it another way, or replace it, assuming I can ever find a replacement shaft with a taper PTO end like that. Or enough extra crankshaft length to whittle it down to that.

08-12-2007, 02:25 AM
Hello JT
Years ago we used freon inside the shaft to remove steering wheels quickly.
When we squirted some in the spring would usually push the steering wheel off. I like Ian's suggestion of tacking a nut on the outside of the rotor and pushing it off with a bolt in the nut. You could take the nut off with a grinder by cutting the welds. Using that method you could cool the shaft inside with dry ice and then put the bolt in and impact it to push the rotor off. I know today freon is not used for that but the cooling principle could be used before attempting to push it off with the nut and bolt.

08-12-2007, 02:46 AM

A.K. Boomer
08-12-2007, 10:21 AM
Here is what Id try, It sounds like you got a real stubborn one and you need two systems at once --- I can see your brass hammer marks on the bolt end and that is a gallant effort but you need to apply massive amounts of pressure while doing it.

I see an angle on the outer parimeter of the rotor slots, find a bolt head that slides in at an angle and then straightens out and locks its lip of the head on the inner side, this will give lots of pulling power as the bolt cant move outward, you might even have to grind an angle on the outer head of the bolt and thats fine, now make up 7 of them and a thick flat plate with 7 holes to keep a straight pull radius, have the bolts threads long enough to lock a nut on one side and a nut on the pulling side, Youv got enough metal involved to pour the coals to it with 7 fast made pulling jaws, Your flat plate has a massive center bolt with massive nut welded to it (preferably on the inside if youv got the room) last but not least, a makeshift "arm" welded to it to counter-act the torqe from the bolt, ----- many of mechanics leave this detail out but if your tightening against the 7 bolt heads themselves you will loose a good portion of your torqe aplication and stress the holding power of the bolts, after you get an ungodly amount of torqe aplied stand back and give the head of the puller bolt a quick "wap" or use an air hammer which is what i prefer, better to have many of sharp little vibes rather than one big one for loosening, (much safer for everything also).

Edit; I just went back and looked at that outer rotor angle and you might be hard pressed to get a bolt head in that way, If thats the case the thing I would do is mill two flats off the peak sides of the bolt heads 180 degree's opposed, then insert heads and rotate 90 degree's, the bolt heads should leave next to no play against the outer and inner rotor and should be deep inside the outer as I wouldnt want to count on the thinner outer rotor edge to keep the heads in contact with the inner even though youv grid locked the bolts to the plate there will be concern there... Like everybody else including yourself has mentioned --- heat is the "tripple wammie" that can be applied, but like you so wisely stated, id also stay away from it in this aplication. Good luck with whatever you try.

J Tiers
08-12-2007, 11:11 AM
Edit; I just went back and looked at that outer rotor angle and you might be hard pressed to get a bolt head in that way,

Yes, max clearance thru there is 5/16 inch, and that is at an angle.
That is the last resort, as it requires a lot of work and has been evaluated as likely to simply result in mashed puller parts.

The size of actual part that can really be slid in and hooked on is pretty tiny.

So far it's oil and whacking the end. persistence often pays off. if it does not, I may have to try the puller.

Yeah, welding and so forth sounds like a really BAD idea on a permanent magnet rotor............

08-12-2007, 02:03 PM
Could you use a set of expanding hooks that could easily be slip into the hole and then cranked into place... if you know what I mean. Say two pieces of flat bar with J's cut into them a pivot and a screw to push the lower jaws apart applying pressure to opposite lip under each spoke on the hole. Make up 3-7 use a plate with center bolt as a puller. Or figure out away to add a catch lip to use your gear puller. Yah I know sounds like abit of work but just another idea.

08-12-2007, 02:09 PM
Could some U bolts be slipped into those openings? Might be a bit easier than grinding a bunch of straight bolts. Just a thought.

08-12-2007, 02:33 PM
Is it possible to build a spider of pullers such as this (ignoring the off-plumb hand drawing errors):


08-12-2007, 03:10 PM
Hello Again JT,
I don't believe Small tack welds on the hub would cause any heat damage to the rotor. Molecular alignment should only be affected in the immediate weld area not through the entire piece. So two areas on either side of the nut about 1/2" long should work. Current would have to travel through the whole rotor to change molecular alignment. The closer to the center of the hub the better the puller will work. What do you think?

J Tiers
08-12-2007, 03:26 PM
Well, persistence pays off, as always.

After several days of tapping when I went by, today as I was on my way to feed animals, I gave it a few more whacks, and the hammer note changed. Sure enough it was loose.

Looks like an old standard "truism" is wrong...... I did "keep doing the same thing in the same way" and yes, I WAS "expecting different results". And I GOT different results..... !

So, I guess it works to be crazy, or else the person who wrote that IS crazy.