HCCT Magneto Coatings - What, if anything, needs to be bare?

[namdc3]

In a car, all of the flywheel and magnet-mounting parts are bare and get continually coated with oil. The field coil ring is coated, but the coil post surfaces are bare. On an HCCT, it would be nice to protect these parts from any future corrosion. This got me to thinking, what surfaces and contact points actually need to be bare? Magnetic field lines generally travel through non-ferromagnetic coatings freely (I think), so the coating (like paint) would only be decreasing the magnetic field by the physical separation distance created (thickness of the coating). Yes, this is proportional to the distance squared, but the distance is tiny. I could see where having the outer surface of the keeper plates be bare would help with adjusting keeper height more accurately, and I can see where having the coil post surfaces be bare would help with adjusting the magneto gap more accurately. However, is there really a need for the magnets to have metal-to-metal contact with the keepers? If so, anywhere else? Once the keeper heights are set, any reason not to paint the outer surfaces since there’s a generously toleranced air gap to the field coil posts anyway? Magnet experts, feel free to school me.

[Kerry]

HCCT, just spray that with WD40.

[Humblej]

Nikolaus,
I cannot answer your question regarding electrical and magnetic properties being impacted by coating the mag parts, however, I can tell you corrosion has not been a problem for my HCCT for the 50 or so years I have owned it and kept it in a damp basement, garage, and sometimes in storage. I would recommend you send your meter to Bob Cascisa for calibration.

[Ron Patterson]

I have restored over 50 HCCT's so I qualify to opine.
This procedure will address your painted surface questions.
This process is for a Ford /Ford clone HCCT.
With the exception of the spark ring mechanism (I will address the spark ring later) everything may be painted. Do not paint electrical connections.
Totally disassemble the HCCT, including the flywheel. The flywheel is cleaned and painted. The magnets were cleaned, crack checked, recharged and assembled onto the flywheel with new screws and clcmps using Brass or new (do not reuse aluminum spools) setting the magnet heights with a KRW Gap Gauge. I then spray paint the entire assembled flywheel and hand paint the rebuilt field ring with a brush covering all the myriad noooks and crannies leaving the solder pile and field ring mounting machined surfaces (these are electrical connections ) unpainted.
I clean and paint the HCCT cast iron frame, install two new shaft bushings (driveshaft front bushings) in the casting.
Install new wood pieces in the coil test slot wood. Prewire the fame and coil test slot, field ring and meter connections leaving the wire to the meter long enough to connect upon final assembly. Install the field ring on the frame, make and install new Delring spark ring insulators onto the field rign mounting bolts. Under no curcumstances should you drill the 1/4-20 spark ring and 3/8-16 field ring mounintg screws/ bolts entirely through the length of the Delrin spacres. Mount the meter and connect the electrical connection to the coil test slot. The metere mounting screws will provide the meter ground connection.
Mount the flywheel assembly and set the (.025) magnet to field pole gap.
Now about that pesky spark gap. The tip of the rotating gap brass pointer should be rounded with a radius of approximately 1/8 inch (NOT SHARPLY POINTED!!!) with the spark gap set to 1/4 inch 360 degrees around the circumference of the spark ring inner radius You may have to shift the spark ring around to get a consistant gap measurement.
The following is is very IMPORTANT. The spark gap (radius of the rind and pointer tip) must be kept clean.The high voltage. low current sparks across the gap loves to corrode and if not kept clean the HCCT will soon quit sparking. I Nickle plat the spark ring. I also suggest cleaning the entire gap of the ring and pointer tip with a small stainless bristle wire brush before each use. Most HCCT new owners are not aware of this issue and when the gap stops sparking the reduce the gap to get it sparking again. A properly adjusted coil should provid enough energy to jusp the 1/4 inch gap in free air if the spark gap is kept clean.
The HCCT is a great tool, but it is a trap for logical people and is only as good as a man with some experience operating it and knowing the correct indications.
Have fun and don't get shocked.

[Ron Patterson]

Notice the small piece of emery cloth?
Thats for spark gap cleaning.

[namdc3]

Thanks to Jeff and Frank. My concern on WD-40 is that is won't last and it will attract dirt, etc. Frank, I'm surprised the bare magnets haven't surface rusted in a damp basement. Kansas City humidity would take its toll I think! Yes, Bob is definitely the meter guy! I have purchased from him before, and he does beautiful work.

Thanks, Ron, as well. There's a wealth of detail there. Yes, I learned the spark gap cleanliness issue on my SSEC tester - the pointer actually makes a brown dot at every other spark location because of the A/C electrons switching jumping directions (pointer to ring, then ring to pointer, etc.).

Your method described would leave no exposed metal to rust, including the outside surface of the keeper plates and the field coil ring posts. You DO have metal-to-metal contact between the magnets and keeper plates since you assemble them before painting. This would perhaps help the plates couple to the magnets slightly better than painting all parts individually and then assembling. I still think painting all parts individually and then assembling would work, but perhaps your method makes for more mechanically solid connections for setting and maintaining heights.