Generator Field Coil Screw

Stinch

Stinch

Senior Member
How hard is it to remove each of the two screws that hold the field coil mounting shoes to the inside of the generator housing? My housing are in decent shape with not much rust and mostly oil and grease having protected them for many years. I'd think a hand impact drive would work with a large bit. Can't seem to find one that is big enough and fits tight. I'm hoping to save the screws and not bugger them up.

Rich
 
It's hard. You have three or four choices: (1) Take it to an automotive electric repair shop: they have a C-Clamp tool with a blade on the end of the auger that will turn it loose: (2) Use a punch and a 3 lb hammer, place punch in screw slot and hit with hammer in a counterclockwise direction: (3) secure the generator on a drill press, put the appropriate blade into the bit, lower the bit into the screw slot, and have a friend turn the bit with a pipe wrench: (4) use a hand impact drive with a decent bit and a heavy hammer. It's impossible to save the screws from damage: new screws are cheap. The screw itself has a concave shoulder that fits into a receiving recessed pocket: the threads on the screw thread through the tube and into receiving threads in the field shoes. When you replace the field screws, put them in VERY Tight. Good luck.
 
I bought the properly fitting bit from Snap-On for my hand impact driver. It still wasn't enough to get the poles pulled in as tight as they needed to be. I had to take it to the local generator/starter rebuilder. I hope to make the tool for the screws soon.
 
IMO every club/chapter/region should have such a tool for the benefit of members. Using it, a 2-3 hour frustrating job can be made into a 1-2 minute job. It could be used for generators and starter motors. I have seen two bench top such devices for sale on some little known auction site. They both work on the same principle, i.e., unrelenting pressure into the screw slot, then a twist. One of the tools on that auction site went for $75 before I had a chance to bid. The other tool closed out, unsold, because the entry price to bid was $250.
 
Some of the repop shoes have an incorrect shape, some have used a hex bolt to draw it tight to the casing, once pulled tight remove the hex bolt and install the correct screw.
 
Don't know. My practice is to remove the shoes, wipe the shoes and the inside of the tube with acetone, then a clean rag. This is to remove the light film I find in the tube and on the shoes, sort of like the almost invisible build-up on a well-used battery terminal. Then I wire buff the inside of the tube near the screw hole; and, I wire buff all sides of each shoe. I replace the shoes. I check the armature for free and easy spinning with NO touching of any shoe. If there is a click or a scrape of a touch, I remove the offending shoe and wire buff the high point. My goal is to achieve minimal clearance without a touch of the armature to a shoe.

Draw the shoes tight each time with a hex bolt as Steve said.
 
As Bud mentioned you want minimal clearance without touching. I don't know what the Ford blueprint called for, but it's probably less than .010" clearance. I worked on a couple generators where everything checked out, but the output was low. The only thing I found wrong was the clearance was a bit too much. The magnetism diminishes as a square of the distance, so a lttle extra clearance means a much larger drop in output. Never cut the rust off an armature by cutting it in a lathe. Carefully use of the wire wheel will remove the light coating of rust, if there is any.

When the starter bushing gets a bit worn then the armature starts dragging on the field poles, so this shows how close they are, both on the starter and generator.
 
BudP said:
(3) secure the generator on a drill press, put the appropriate blade into the bit, lower the bit into the screw slot, and have a friend turn the bit with a pipe wrench:
Click to expand...

This afternoon, I did quite well with removing the two field coil screws out of my generator housing. The generator field coils were burnt to a crisp from a decades old problem but I was still able to pull the armature out.

I found an old large flat bladed screwdriver that was missing its handle and the tip was smashed from having been used as a chisel. The tip was ground down to match the slot in the screws. Using Ron's third option, I put the tooling in a drill press and the housing lightly in a vise. Once everything was setup, I took the housing outside and "shocked" the screws with a oxy/act torch for about five seconds. Once back in the vise and drill press, the screws came out easily with a twist of the screwdriver. The mounting shoes were hot but I don't think hot enough to damage a good set of field coils. In this case my coils were shot anyway so I had nothing to lose. In the future I may reserve the torch for stubborn screws. Maybe beginners luck, but this seems like a good way to go.

Rich
 
0ne of the first tools I made for generator and starter work was a pole piece expander --I started with a piece of pipe about the armature diameter, cut it in 1/2 and used a muffler pipe expander to force the pole pieces tight--the muffler expander didn't go large enough the pipe pieces were shims ---then I worked the screws with a ground to fit drag link socket and hand hammered impact.

As Tom says--as close as it can, but never touching ---I have found that most gen armatures that touched were shorted
 
Here are a collection of tools used to rebuild generators: http://www.holtkampelectric.com/Shop.htm

Blow the picture up and you will see the screw removal tool on the far right. It has a padded V - shaped base to hold the tube, a press handle to push the bit into the screw head, and a turning handle to develope torque and twist the screw. Note also the other equipment on the bench including the analog meter, very handy for working on a Model A.
 
Stinch said:
How hard is it to remove each of the two screws that hold the field coil mounting shoes to the inside of the generator housing? My housing are in decent shape with not much rust and mostly oil and grease having protected them for many years. I'd think a hand impact drive would work with a large bit. Can't seem to find one that is big enough and fits tight. I'm hoping to save the screws and not bugger them up.

Rich
Click to expand...
I have rebuilt hundreds of starters and generators and at the time had all the tools including a pole screw removal tool which I seldom used. I had an easier way! Grind an air chisel tool to just fit the slot of a good scew. Support the case or yoke in a big vise, add a penatrant then "rattle" the screw with the air chisel. This will loosen the screw and straighten the ones that someone has buggered before you. Most every time you can then spin the screws out with a big screwdriver.
Rainmaker Ron
 
For those who do manage to remove the field coils, be sure to put them back in the same location. You'll have problems if you switch sides.
 
I use a drain plug wrench which has 4 different size squares on each end to fit various size drain plugs on transmissions and rear ends. Actually one is like a screwdriver blade. I filed one of them down slightly for a good tight fit in the field pole screws. Using a vise I put the gen or starter frame with the wrench inserted in the screw between the jaws. Since the wrench is less then 1 inch thick at the and the handle is at right angle to the screw gives plenty of leverege and the vise holds it all together tightly. Haven't had a screw yet that didn't loosen. Gas stations used these wrenchs since they fit everything.
 
Kurt's idea of a pole spreder is a good one and the local generator shop also uses one. I haven't seen their jig for removing the screws, but he wouldn't tighten my Cub Cadet starter/generator pole screws until I removed the armature. The spreader will better press the pole shoes to the case as well as prevent any chance of distorting the case while pressing hard into the screw head. I have a large steel bar that will fit through the center of the case and while the bar ends rest on supports, then the screwdriver blade will be run into the screw head. I'll make this tool by welding a large square out of square tubing. Maybe this winter I'll get it done.
 
I saw a tool for removeing the screws years ago in a Chevy manual. All it was is an arbor press with a bit on it that you could twist.

TG
 
I got to take a picture of the pole piece expander and screw remover I have now, KRW ones that were never used before ---I don't think they are the best design but they work better than the modified muffler expander I used to use --the expander doesn't go small enough to easily go in with new field coils that aren't perfectly formed.
 

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