Some previous owner tried to pull starter w/o removing bendix. The mag shows a short. Otherwise it's in great shape! Engine and tranny are out and disassembled.
Can I just bypass this magnet section, instead shipping for a total rebuild?
'15 Touring w/starter
If everything is apart, and electrical issues not withstanding, I wouldn't remotely consider it.
I believe you can.
I also believe you can replace the single coil and leave the rest intact if you so wish.
First. How are you determining "The mag shows a short."? If you measured the mag to ground? They are supposed to. In a properly working magneto coil, the one continuous alternated windings coil is grounded at one end, and connected to the ignition system on the other. It must be grounded because the ground is a part of the electrical path for the ignition system.
If you need to determine whether coil windings have grounded themselves? You first must disconnect the last coil from the ground. All coils loop from one to the next, from the mag post "button" all the way around to the final (first?) coil on the other side next to the mag post "button". Just follow the ribbons of copper, easy enough to see. An important caution. Best to not disconnect the last coil from the ground at the point where it connects to the cast iron coil frame. When they were made, the iron was fresh and new. A rivet and some solder worked okay. After nearly a hundred years, many of them soaking in oil, reconnecting it to the cast iron is nearly impossible, although most still work fine on the original connection. Instead, cut the ribbon between the coil and the ground. Be sure to leave enough of each end to solder them back together with a short copper bridge.
If you find continuity to ground still from the mag post "button"? The only way to determine which coil is going to ground is to cut the ribbons between coils and isolate them till you find the one shorted to ground. A technique used in the business is to "halve" the remaining coils (half on one side of the cut, the other half on the other side, one half should be shorted, the other should show open) and follow the short till you find the one coil that is shorted.
Bypassing one winding is a bad idea. It may work if one is stranded in the wilderness and needs to take extreme steps to get back home. The coils are alternated, and will not work very well with one missing.
Frankly, the damage to yours is relatively minor. With the hogshead off (as it appears to be), you should be able to carefully use a needle-like pick to lift turns in the damaged area. Then clean as well as you can. Push good epoxy (the more heat and oil resistant, the better) into the damaged area. I use electrical tape to create a form around the repaired area to hold the epoxy into place until it has thoroughly set. Use slow setting epoxy, and do not remove the tape too soon, as it might pull the epoxy out of where you want it to stay. You may also want to put a second coat of epoxy over the repair for added protection.
The reality is, that if one or two turns are shorted to each other (NOT to ground!), it will affect the efficiency of the magneto some, but not a lot.
You can also replace single coils on a mag ring. It is easy to do, provided you have a known very good coil to put in. I have replaced a few over the years. (I am too broke to buy one of those wonderful rebuilt coil rings which it looks like you already have.) IMPORTANT! Be absolutely certain the coil you put in is wound the correct needed direction! Again, the coils alternate direction of windings.
Questions. Was the car running before? When you got it? Did you measure magneto output at the mag post? Did you measure for AC voltage (model T magnetos are AC, a DC meter will register 0 )? Have you checked the magnets for their strength?
If you had no voltage at the magneto post, did you take steps to be sure the failure was not the post's connections itself?
As I said, the damage looks fairly minor. From what I can see in your photo, I would be surprised if it didn't work due to that little damage. Even marginally poor condition magneto rings often work quite well.
The starter damage certainly is there. But I doubt that would be the source of magneto ignition failure. I have seen working magnetos pulled out of old running engines that had nearly half the outer insulating wraps GONE!
Have fun! Good luck!
to find where the ring is grounded, a small DC source may be applied to the button and frame. A magnetic field showing up at each sequential coil from the "button" indicates continuity to that coil. The first dead coil is the ground path. There is no need to cut each and every coil from the other.
My first response was perhaps unclear to the question "can I bypass this magnet section, instead shipping for a total rebuild?"
This is not meant to be harsh, but to make you think and consider the value of your time vs. the value of a dollar. From your description, the engine is out of the car, with engine and transmission apart. You apparently don't know how the magneto works, but are considering working on it to the point of altering its design. Following that you will totally reassemble the engine and transmission it to test it.
Now I'll ask YOU a question: if it doesn't work after that effort, how expensive did a $219 professionally restored coil really sound to you in the first place?
I had a similar problem a couple months ago, a magnet clamp screw broke and damaged a coil. It was a rebuilt coil, not terribly old, so nothing rotten. I checked it as mentioned above and it was good and I recharged the magnets while I had it apart since one had broken, then I found 2 or 3 more cracked ones. I’d do that as well if you have it torn apart anyway unless they are good.
Every time I put a motor together if it’s not too tight like a rebuild I test the mag before ever assembling the transmission to the Flywheel. I clip a test light onto the copper strip that goes to the contact button, the light to the motor and give it a spin. That lets you know before you’re too far along. I’d hate to put one together and it not work and have to take it all back apart.
With the mag ring out of the engine and on the bench, it can be easily tested using a low voltage alternating current supply. I use a variac and 3 to 4 volts across the whole 16 coils, then measure the voltage across each coil, should be 1/16 of the total applied voltage. You can also measure the voltage from each coil to the ring, looking for a short to the ring. The coil that is riveted to the ring will not have much voltage on it. I have re insulated many of these with very good results.