Bosch AB33 Mag coil replacement

[Dave from Omemee]

I have the armature out of my Bosch 33 mag. Its off of my 1.5hp FM Z.
The coil is open circuited on the high tension side. The high tension slip ring appears to pull off after you remove the spring wire, but how is the high tension lead connected to the slip ring? Is it a connector that pulls off with the slip ring?? Are there screws under the high tension slip ring??to disassemble the coil pole piece.??
Has anyone tried to rewind one of these coils?? Does anyone know the capacitor value??
Thanks
Dave from Omemee

[Andrew Mackey]

I sure hope you didn't take the magnets off the case - if you did, toss the mag in the trash, and buy another one! As for the core - try Marks Magneto Service, or H&M Enterprises - they advertise here at Harry's. One Hi Tens. lead off the coil is soldered to the slip ring. One is grounded, along with one from the lo-tens. thr other lo-tens. goes to points and condenser.

[Dave from Omemee]

thanks for the advice. Can you not recharge the magnets?? How do you unhook the high tension lead from the slip ring?
thanks
dave from omemee

[Rudy]

Whatever you do , don't throw the mag in the trash. I remove the magnets all the time never had a problem. It gets done at most mag shops to bead blast the case and reassemble. The wire does not get soldered onto the collector ring. All you do is strip the wire and when you slide the collector ring on it slides into the hole. then the snap ring holds it in place.. Just be careful when you recharge the magnets that you do it right. There is a special procedure to do this. Nothing happens to the magnets if you take them off. They just get a little weaker and then need recharging. Magnets are magnets!!!they do not have a mind of there own, I have never seen a magnet swap poles end for end or whatever. I have repaired quite a few of these and when done right you get a 1/4 inch spark. Dave, did you get the e-mail that i sent you the other nite?

[John Ledbetter]

Originally Posted by Rudy

Whatever you do , don't throw the mag in the trash. I remove the magnets all the time never had a problem. It gets done at most mag shops to bead blast the case and reassemble.

Rudy, I was going to tell Dave not to trash the magneto, that I would take it off his hands, because I have not figured out how removing the magnets would destroy it. But then again, I'm not an expert on mags..

[Andrew Mackey]

Unless you have the special pole pieces and the proper mounting for recharging the AB -33 and 34 mag, the magnetic loss will render the magnets nearly worthless. If the mag is properly re-magnetised, I agree - a 1/4 to 3/8 spark is possible. I had a AB-33 re-worked by an excellent mag man, now deceased, and he soldered (tinned is a better word) the wire for the slip ring. He said thet the wire tended to corrode, increasing resistance, one thing these mags don't need. This mag threw a 3/8" spark, and I won't hold the wire on this one to see if it's hot!
Andrew

[Rudy]

John, removing the magnets does not destroy anything. The bosch AB-33 mag has gotten a lot of bad raps in the past. They are a little tricky to repair. The problem is that in the shuttle wound armature there is a lot of stuff crammed into too small a space. There is the primary winding, then the secondary winding over top. Then in the rear of the armature is the condenser . Most of the time the coils on these mags are shot. You remove the covering and the windings will be full of green corrosion. The other problem was on some of these mags the magnet material was not of great quality. Some hold magnetism and some loose it more quickly. Most mags had a horseshoe magnet . On the AB-33 there are two flat bar magnets. The cast end of the mag where the point plate sits in, straddles the two magnets thus completing the magnetic path kind of like a horseshoe magnet. This is why it has to be charged from the front/trip side of the mag. I have repaired quite a few of these mags and have never had any problems with magnets reversing polarity or anything else strange, like that.If you remove the magnets for a period of time just configure them the same way you took them off and put a keeper across, just to keep some of the magnetism intact.As far as the front collector ring goes,it slides onto the front shaft and the wire just pushes into the hole on the collector. This is the high tension side and this is how they were built and the current has no problem making a good conection, in there.Hope this sheds some lite on the subject.

[Harry]

So, let's shed some light on this little jewel, but if it ain't broke, don't fix it! Mine had no spark due to corroded points.

Here's the charging setup...

Above, Joseph Sr. (110VAC) is in the background and little Joseph Jr. (12VDC) is in the forground. The blocks around the magneto are soft iron, which easily conducts the magnetic flow without holding a charge themselves. I realized after taking the photo that I had two additional blocks that would have added to the pathway. With this setup, the AB33 gets a good charge. Be mindful of using north to south and south to north when setting it up.

As seen in the photo on the right below, the mag springs are tensioned counter clockwise and then it trips clockwise until the points are opened by the block in the upper left of the rear housing.

The points had to be disassembled in order to use a jeweler's file on their build up of corrosion. If you remove the side screws in photo #3, it is very tricky to get it put back together without it getting away from you. (One of those parts hunts on a dirty shop floor is awe inspiring!) If it ain't broke, don't fix it! Also, be careful with the mica insulation under the center screw that holds the fixed point. The moving point is at chassis ground potential. The fixed point is insulated and is connected with the mounting screw to the primary coil terminal in the center of the rotor shaft. The active lead from the condensor is connected internally to this point.

The large brass ring at the left of photo #2 is at ground potential and a carbon springed wiper with brass screw connects it to the main frame. The common internal terminals of the primary coil, secondary coil and condensor are all connected to this point.

The slip ring at the right in photo #2 is connected via a springed carbon wiper to the top spark plug lead. The output lead of the secondary coil connects internally to this ring.

The two brass screws at the bottom of photo #4 are locater pins for mounting the mag upon the governor. The mag is held in place on the governor with a clamp as shown here.

[Andrew Mackey]

Nice picture Harry,
Is the charger yours? I haven't see one like it in years!
Andrew

[Harry]

Thanks. Yes, I picked that up a few years ago. Quite handy to have.

Now, to figure out whether to rewind that coil. Someone must have the wire sizes and turns count for the primary and secondary? Condensor value?

[Rich Martz]

Thanks for posting that picture Harry. I have a couple of those mags and I'll try to charge them before I send them out to be fixed.......

[Harry]

I later added some additional bar stock to the sides.

I'm also thinking of trying to charge it up-ended by removing the trip arm and spring collar pins. Damming it up for the proper magnetic flow with the trip end down and the points up.

You may need to clean the points. Ted Brookover and John Rex indicate that the insulation is very poor in these coils and that rewinding is the way to go.

Here's my project page: http://www.old-engine.com/fairbnk2.htm

[Harry]

I don't know how many of you have been brave enough to dig this far into the world of electronics, but this photo tells it all. I melted and dug out the old tar covered mica glob of a condensor and soldered in this nice new one. A small amount of silicone calk will be placed under it to hold it steady as it turns in circles with the armature. Once the cover is sweated back on, the antique world will never know it's there and the mag will have all the microfarads that it needs to offer up a good spark.

Just so you know, the condenser body terminal goes out the back through an insulator to the points via the contact set mounting screw. The strap to the insulated condenser terminal is screwed to the rotor common. The high voltage coil return is common and the low voltage coil return is at common. The low voltage coil high side connects to the insulated condenser can. (A small nightmare, but it works.)

[ListerDiesel]

Excellent bit of work and shows what can be done with a bit of thought to keep the old stuff running.

Peter

[Ernie D]

I just went though all of the above on my AB33. It was working good and then just quit. So apart it came. Secondary was open. A couple of phone calls to get the coil rewound. www.magnetoparts.com (One of Harry's adbvertisers) While waiting for the coil I removed the condensor and replaced it with a new one and potted it on epoxy. While apart I removed every piece that could be removed. I DID mark the side pieces and the case so they could go back where they were. I got the coil back and reassembled it. By the way it had NO noticable magnetism. Once it was together it actually had spark. Not much but it did spark. So just for the fun of it I put a couple of speaker magnets on the sides of it. It puts out a good 3/8 in spark. So this weekend at the Bernardston, MA show I will get it charged.
So take it apart yes (Mark the parts)
Throw it away NO
Get the coil rewound yes
Replace or have the condenser replaced yes
Clean and adjust the points on reassembley yes
Recharge it yes (you will have to) It is NOT possible to take an AB33 apart without loosing the magnetism.
And one last thing make sure REALLY make sure you don't mix up the screws from the sides. The 8 screws that go through the magnets are short. The 4 screws that go into the sides of the end plate are longer. If you interchange them there is a real good chance you will ruin your new coil!

[Ernie D]

So after all of the above I have taken it off the engine and am now using it for a welder. It has a good 3/8 in spark and at a normal plug gap it has a huge blue spark. Thanks Bill for the magnetical molecules!

[earniemanson]

hi all
i see that harry and a few of you have rebuilt these things is it possible to have one of you rebuild my ab33

[MarylandSteam]

Originally Posted by Andrew Mackey

Unless you have the special pole pieces and the proper mounting for recharging the AB -33 and 34 mag, the magnetic loss will render the magnets nearly worthless. If the mag is properly re-magnetised, I agree - a 1/4 to 3/8 spark is possible. I had a AB-33 re-worked by an excellent mag man, now deceased, and he soldered (tinned is a better word) the wire for the slip ring. He said thet the wire tended to corrode, increasing resistance, one thing these mags don't need. This mag threw a 3/8" spark, and I won't hold the wire on this one to see if it's hot!
Andrew

Do you recall the "magmans" name or location?