i am in the process of mounting the field coil and have a question. in order to get the correct clearance i had to put two shims in the two inner mounting holes of the coil ring. the supplied shims are .33 th. this results in a similar gap of .20 th. at the top and bottom. will this cause a problem when the engine is in the normal running position? the installation was done with the engine in the vertical position. what can be done to increase the gap to the recommended .25 th.

Bill, are you also saying that you did not have to place any shims at the other two bolts? If so, that would seem strange to me- like something is crooked or warped (like the field coil ring).

Otherwise, I'd suggest just taking out maybe .006" off both shims and trying that. Remember, the recommended clearance is between .025 and .040, so shooting for around .030 is not a bad idea in my mind. Yes, I do realize that the closer you get the stronger the juice, but that also gives you less room for error.

Mike (I'm also in the process currently of setting the clearance on my rebuild...)

Bill,
By putting the shims at the inner (top) mounting holes, you are moving the top of the ring toward the flywheel and the bottom away from the flywheel. Have you rotated the flywheel and measured the gap all the way around? If it varies when you rotate the flywheel, your magnets are not at even heights around the flywheel. Or it could be caused by all four of the flywheel bolts not being tight. It should be within clearances at all poles and in each position as they pass the coils. Try placing thinner shims and measure again. The .025 is the minimum clearance. The reason for that clearance is to compensate for expansion and contraction with temperature and vibrations. You can get shim stock in various thicknesses at the auto parts store and cut your own and not have to order and wait for it to arrive.
Norm

Bill: Are you using the pealable mag shims? They a laminated shims of .002 each. JP

Then too, any area with less than about .028 may cause a great deal of grief later on. Any area with a gap greater than about .034 will also provide a very low Mag output.

Bill
Whatever gap you select, I like .030, I suggest adding .005 at the bottom of the field ring to allow for vibration of the lower (unsuppported) portion of the field ring.
Ron the Coilman

Ron, so you recommend that I set the clearance to .030 all around and then slip in .005 additional shim at the bottom? Any idea what clearance that would result in at the bottom and top? Seems like it would yield a clearance of less than .025 at the bottom where the heavy transmission may reduce the clearance even more when vibrating or bouncing.

I'm just trying to better understand this as I'm right in the middle of getting my clearance set also.

Thanks,
Mike

Mike
Shim the field ring to engine mounting points however necessary to yield .030 magnet to field winding pole gap at the very top and .035 magnet to field winding pole gap at the very bottom. Check the side gaps for a gradually decreasing gap as you move up both sides to the top to ensure you do not have it cocked. Rotate the flywheel to ensure each gap stays the same regardless of flywheel radial position.
Ron the Coilman

Okay, I understand now- that you increase the gap at the bottom by .005"! Makes much more sense to me.

Thanks,
Mike

Mike
You got it.
If you take a close look at the field winding casting mounting you will notice it is supported on the rear of the engine block only on the top 180 degrees and the bottom is just hanging out there. Because of the attraction of the magnets toward the winding poles the casting frame flexes. It is very common to find field ring castings with cracks around the lower bolt holes from this flexing. I am told the early Model T stamped steel field winding frames were very bad in this regard. The two field winding ring re-builder's I recommend are aware of this problem and carefully inspect the frame castings for cracks.
Good luck and hope this helps.
Ron the Coilman