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Christmas 2008 - Magneto Tech
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-The Vital Spark
 By Grizzy

Over the last few years I have had quite a few Joe Hunt magnetos pass through my hands for converting to be used on our chosen steed, be it Chief or Scout, of the latter day that has a dizzy sticking out of the oilpump. I am not set up on anything like a commercial basis. I work out of a 20ft shipping container that I also keep my bikes in, or in God's own workshop (al fresco) which is a bit drafty but it has nice high ceilings. The fact is that I am doing it very much on a DIY basis, which is also quite time consuming (I couldn't charge by the hour - it would have to be by the week!). Anyway, I thought I would show how it is possible with the appropriate knowledge, and for those with time on their hands, to be able to fit one of the best looking accessories that ever graced a hot ride or trick Indian bobber.

Most of the Joe Hunt type magnetos that are available, and most suited for Indian, come from the old H-D "Iron head" Sportster. Any magneto shop that supplies spares would know it as a Fairbanks Morse type FM-X1-2B7 Simultaneous Spark. Armed with this knowledge you should be able to get a contact breaker points set, condenser,  bearings and coil. At least this will ensure you get a good spark to start with.

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Merry Christmas!

I won't go into "How To Strip A Magneto" as I assume, if you are about to attempt this conversion, that you are a competent mechanic. And if your not it will stop you buggerin' up what is fast becoming a rare artifact from last century.

The one thing that I would ask you to keep an eye out for is the points base. This seems to be made of crap and needs an softly-softly, approach. It also holds the top bearing. Just make sure that, after you take out the four countersunk screws, that the base is loss before you drift out the rotor. I have had them crack up because whoever was last there had used a very powerful Loctite type of product that not only glued the four screws into place but also the base to the caseing.

This is another inspired lead that I would never of got into without the VI. Back in the day, one of our listers, Craig, was privvy to the boss man of Joe Hunt's notebook (some scoop!). And in there was the cam grind of  H-D at 45 degree and the 42 degree of the Indian grind. Looking at the drawing (fig 2) it all makes sense if you break it down to the leading face that lifts the heel of the contact braker .

The close down of angle from H-D (inner circle in fig 3) to Indian (outer circle) is the only part that I have ever altered, as I feel 3 degree diferance on the dwell angle is hardly worth considering. In fact, I think it was Cotten who pointed out at the time, that: "If you don't bother to grind at all and, share the discrepancy between the H-D and the Indian timing between both cylinders, at 1.5 degrees out each, it  will still run better than a worn dizzy" (or words to that effect).

My dial gauge is just a timing disc with a 1/2" tank conector from a plumbing shop, the compresion olive fits the drive side of the magneto rotor perfectly.

I have used some scrap angle brackets with a V cut in each for the rotor to sit in, and a pinch bar  just resting on the top one side so the contact breaker (points) spring does not lift the bearing surface out of the V. The contact breaker points are mounted on stiff plastic with a 12v bulb wired so that when the contact breakers are open the light is off. I set the contact breakers at 5 thou, I found that suited what I was working with.

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Fig 2. Drawing from Joe Hunt's notebook. Letters in text (D, E etc) refer to this, and to some extent to the sketch below.
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Fig 3. Inner circle is H-D timing, outer circle is Indian timing.
Now we get to the important bit .The cam on the end of the rotor has a fat side and a thing side. It will be the thin side that is the static leading edge and the fat (D E in figure 2) is the leading edge that is altered. II set it up so that I can file it of with a good cainsaw sharpening file. File? (I can hear the disapproving tuts already) Yes, file! It's not hardened to anything like you would think.

To get an even stroke of the file, I first mark the leading edge of the fat side with a marker pen, evenly file that off, then try the dial gauge each time. Repeating the process of marker pen and file untill the angle is closed down. Like I say, time consuming. But it can be done like this; personaly I'm up to number 9. I know that doesn't make me an expert but at least I've got a head start on you blokes!

The turret that the mag sits on is far too tall. I cut the mushroom (outer) bit down to 3-1/2" (90mm) face to end, and the drive shaft at 4-1/4" (108mm) end to end. There is a six-sided male end of the drive shaft that fits the rotor in the mag. The other end I cut into a tang of 1/4" (6mm) by 1/8" (3mm) that fits into the oil pump dizzy drive. I cut the tang at 90 degree to two opposing flats on the six-sided male end. This will still give you 60 degree increments for correct installation when lining up the mag for timing.

The outer turret needs sleeving, and I suggest at this stage a new distributor sleeve will be useful (Indian part number 41373). For those of you without a lathe, you can trot off to a machine shop with the mushroom shape thing and part number 41373, and have a sleeve turned up to fit one inside the other. For those of you WITH a lathe I am hoping you are ahead of me and just getting on with it!

I arc weld a couple of good tacks onto the new turned sleeve on to the turret, cut out a bracket with two holes and arc tack that to the sleeve as high up the turret as possible. Then another bracket that will clamp onto 41373 to stop the whole shooting match from turning in the dizzy hole. The brackets are bolted together with spacer nuts between both brackets.

If I can work it out, anyone can!

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Converted Fairbanks-Morse magneto on Grizzy's Chief engined "Geronimo".

More on the VI here:
Geronimo part 1 (2000)
Geronimo part 2 (2000)

And here!
Grizzy's "DiXiE" Chout (2007)
(part 2 next year?)

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