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 12 volt coils used on most cars in the 70’s and 80’s.  I searched the web for part numbers for a correctly sized replacement, but information on this upgrade seemed to be non-existent.

Bosch Blue Coils

Bosch coils from a Volkswagen, originally installed during the 12 volt upgrade

Next I decided to give Bosch a call, figuring they could just look up what I needed in their vast selection of ignition coils.  This turned out to be a waste of time, because they could only search for coils based on the make and model of a vehicle.  A couple more calls to Bosch Racing and some of their distributors also yielded nothing, so I contacted Dynatek.

Dynatek did not have a coil that was the same profile as the original 6 volt unit, but they did make a pair of compact 12 volt coils with 5 ohm resistance that would work with my dual circuit breaker ignition.  Realizing that this was probably my best option, I decided to take a chance and ordered the Dyna DC10-1 coil set.

Once the new Dyna coils arrived, I removed the “custom” coil cover, old blue coils and bracket from my motorcycle.  I played around with positioning of the new coils until a found a way to mount them which would allow the stock cover to be used.  Basically, I positioned the coils using the original mounting bracket, but with the spark plug wires exiting behind the bracket.

First Coil Fitting Attempt

Initially I tried to mount the coils with the spark plug wires facing away from the bike

Since the front spark plug wire exited very close to the rear cylinder and the rear spark plug wire exited very close to the oil tank, I added a nut and washer to the mounting studs of the coil mount to space it out ~1/4″ from the motorcycle.


An additional nut and washer give just enough clearance for the spark plug wires

I also felt that the coils did not mount as securely as they should and was concerned about vibrations causing one of them to slip out from under the hold down plate.  Using some 1″ aluminum bar stock, I cut two  brackets to bolt the upper and lower mounting tabs on the coils together.  This really made a big difference in how the coils felt when mounted in the stock bracket.


A simple set of aluminum brackets to help keep the coils in place

With the mounting complete, I rewired the ground and power connections, attaching them to the coils with the included ring terminals.  I soldered these connections which should help them stand up to vibrations better than just crimping on the terminals.

The final step was to cut two custom length spark plug wires.  A quick tip on making custom spark plug wires is to check with your local auto parts retailer.  In my case I stopped by Autozone and picked out two of the longest single spark plug wires which had the correct ends for my application.  The cost per wire was only $5.99.  When I got home, I carefully removed the terminal from one end of the spark plug wire, cut it to the length and crimped the terminal back on.

Running Plug Wires

Plug wires cut to length and connected

The final touch was to install the correct coil cover and fasten it in place.


Coil cover installed, ready to ride


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

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