Wiring & Electrics

August 19, 2012

1961-1964 Panhead 12 Volt Motorcycle Coil Upgrade

The 1961-1964 Harley-Davidson Duo-Glides used a dual circuit breaker ignition system (often referred to as a dual points ignition) with a manual advance.  This arrangement meant that each cylinder had an individual circuit breaker that was timed to fire that cylinder’s spark plug.  This also meant that there were two 6 volt ignition coils, one for each circuit breaker.

One common upgrade for motorcycles from the 1960’s and earlier is to change the electrical system over from 6 volts to 12 volts.  When I purchased my 1964 Duo-Glide, the original owner had already made this conversion, but had used a set of 12 volt ignition coils from a Volkswagen.  This arrangement worked fine, but the larger coils needed a “custom” oversized cover to hide them from view.

Original "Custom" Cover

"Custom" cover made from stainless steel by the original owner of my bike

In keeping with my goal of creating a bike that retained as many correct parts as possible, yet was a reliable rider, I decided to try and install the correct coil cover.  I quickly purchased the cover on eBay and then started looking for the right size coils to fit under it.  The original 6 volt coils were 4″ high and 2″ in diameter and looked very  much like a minature version of the More on 1961-1964 Panhead 12 Volt Motorcycle Coil Upgrade

Filed under Classic Motorcycle Maintenance, Panhead Jim's Blog, Tech, Wiring & Electrics by PanheadJim

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August 15, 2012

Classic Motorcycle Magneto Rebuild – Disassembly & Detailed Inspection (continued)

This is installment #4 of a multi-part series by an anonymous friend (not me) who gave us premission to repost here.

5) The magneto has a rewound coil in it, as well as a new condenser (although,  as I wrote in a previous post, the latter already had failed). The electrical properties of the primary and secondary with the armature in the magneto were:

Primary___: R= 0.58 Ohms; L= 3.40 mH
Secondary: R= 4.67 kOhms; L=16.38 H

The inductances would be somewhat lower if outside the housing. For comparison, the primary of one of my two spare ZEV armatures is still good, and it has essentially identical values of R=0.57 Ohms and L=3.52 mH (next photograph).

Although I don’t have a functioning Bosch ZEV secondary to measure, the resistance of the secondary is reasonable, although the inductance is about 50% higher than that of a comparable Lucas armature. My conclusion was that the person who rewound this coil neither made it with significantly too many windings of too fine wire, nor too few of too coarse.

———Sidebar (not in chronological sequence) ———
I am writing the following three paragraphs after the fact. I realized after having sent the magneto back that I should have measured the transformer ratio, which would have told me if the secondary has the correct number of turns. All that is required is to run a small AC voltage from a signal generator through the primary and measure the voltage developed in the secondary. This transformer ratio is ~35 for similar Lucas and BTH magneto armatures. The actual ratio of More on Classic Motorcycle Magneto Rebuild – Disassembly & Detailed Inspection (continued)

Filed under Classic Motorcycle Maintenance, Wiring & Electrics by Buzz Kanter

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August 8, 2012

CLASSIC HARLEY TECH Part 3 – Bosch Magneto Disassembly & Detailed Inspection

Please Note this series of articles is written by a friend who wishes to remain anonymous. I did not write this.

After my initial inspection and test to characterize the condition of this magneto when it arrived, I disassembled it, making notes of what I found to refer to when I started the actual restoration. Disassembly was quite easy. Two screws hold each HT pickup, and a bolt presses the points assembly into a taper in the end of the armature. If this were a later BTH or Lucas magneto there also would have been a safety gap screw to remove (failing to remove it accounts for the characteristic piece broken from so many slip rings).

The photograph in the first of these posts shows there is fairly large gap between the points assembly and the housing so I tried gently prying at the edges and it immediately popped off. Had it not come off so easily, and rather than prying with ever-bigger screwdrivers, I would have taken the time to fabricate an appropriate “pusher” to slip under the assembly and that used the housing to push against (a two-jaw puller would have to push against the screw threads in the armature, which would be fine as long as a the assembly released before the threads had too much force on them). BTH and Lucas thoughtfully provided
threaded holes in their later points assemblies that are used to push them off the armature using the same bolt that holds them in place. After removing the points assembly, and the four screws holding the front plate, the armature was free to be removed.

Overall the components were in reasonable condition for their age, although there were some issues to think over before attacking the rebuild:

1) It has a new slip ring, which looks good. However, some aftermarket slip rings were made with inappropriate plastic that is partially conductive so this requires measurement with a megohmmeter.

Had the slip ring been chipped I have a Teflon mould I use to repair ones on BTH and Lucas magnetos using a non-conductive epoxy with 3000 psi shear strength. If I had needed a mould for this restoration, but had this one not been the correct size
for the Bosch, I would have made one specifically for it. The photograph shows the mould on the left, a new Lucas slip ring on the right, and the chipped slip ring that is on a spare Bosch ZEV armature. However, for a slip ring as damaged as the one in this photograph I would fabricate the missing portion on my lathe and attach it to the existing piece rather than build it up entirely with epoxy (unless it were an “emergency” field repair).

To remove the slip ring on this armature would have first required removing the bearing race. Although I didn’t need to do this, I will describe in a later post how it is done.

2) The bearings appear to be new, but I will inspect the races and the balls with a microscope for any evidence of Brinelling.

3) Although I suspected the leads were of the cotton resistance type, because they felt so limp, their resistances were less than 1 Ohm so they must be made with copper wire. However, even though the insulation looks a bit old I will have to leave it to the engine rebuilder to replace these leads once the magneto is installed, because I can’t guess the correct lengths to use. This will be in the “installation notes” I will send to the engine rebuilder when I return the rebuilt magneto to him. I also attached a yellow tag (from an office supply store) with a note to one of the leads to be sure it wasn’t overlooked.

4) The HT pickups are old, but look to be OK. I made a note to do a more careful inspection of them later, but all three brushes in the magneto looked like they were new.

Unfortunately, there are aftermarket brushes that are much harder than OEM, and these would grind a groove into the slip ring if this is what is in this magneto. An example of this is shown in the next photograph, which is on a BTH armature that was in a box of parts I bought a few years ago.

While the above photograph shows the damage hard brushes can cause, soft aftermarket brushes also are a problem. These slough off carbon too fast and can cause an internal short in less than a few hundred miles. Since there is no sign this magneto ever has functioned since being rebuilt, there is no way to know from the appearance of the slip ring itself whether the brushes have the proper hardness. Since this is problematic, I will replace all three with NOSs Lucas brushes if the diameters allow that to be done. If not, and although I am equipped to measure Rockwell C hardness and could convert to the Shore scale used for materials like carbon, the Rockwell test shocks the sample with a pointed indenter so it is not used on brittle materials. Since this measurement itself could destroy the brush, if the Lucas brushes won’t fit, I have my own tests I will make. Although not as precise as a proper hardness test, it still allows me to determine whether they are appropriate to use or not.

[detailed inspection to be continued]

Filed under Classic Motorcycle Maintenance, Restoration, Wiring & Electrics by Staff Report

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