Roadside Ignition Points Repair on a 1947 Knucklehead
On a cool fall morning, Steve and I left bright and early for the Southern Coalition AMCA Road Run in Maggie Valley, North Carolina. I was riding my 1964 Harley-Davidson Panhead and Steve was astride his 1947 Knucklehead. We had roughly 250 miles to cover, so an early start seemed like a smart idea.
Because we did not need to reach Maggie Valley until later that afternoon, we spent the first part of the ride on secondary highways through small towns and countryside. Our first gas stop was only ten miles from the interstate, so we decided to jump on the highway and make a little better time.
About an hour later, Steve's Knucklehead backfired a couple times and shut off.
Troubleshooting the No-Spark Problem
We rolled onto the shoulder and I unpacked my tool roll while Steve started checking the usual suspects. After a little poking around, he discovered that the rubbing block on the ignition points had broken off.
If you are not familiar with ignition points, the rubbing block rides against a rotating cam. The cam shape opens and closes the points as it turns. Without the rubbing block, the points remain closed, which means no spark to the coil and no spark to the plugs.
Looking for a Roadside Solution
After scratching our heads for a while, I started digging through my saddlebag looking for something that might replace the missing rubbing block. A quick search turned up a fork terminal from my electrical spare parts bag.
Since the original rubbing block was attached with a rivet, we figured we could slide the fork terminal under the rivet and trim it to roughly the same length as the original piece.
Installing the Improvised Repair
Within a few minutes, Steve had removed the rest of the broken rubbing block. We slid the fork terminal under the rivet and used a few solid hits with an improvised punch on the back side of the rivet to tighten everything down.
Steve reinstalled the points and made a couple small adjustments to the length of the fork terminal until the points could open and close correctly.
Making an Insulator from Roadside Scrap
Normally the rubbing block is made from a non-conductive material, so we could not allow the metal fork terminal to ride directly on the cam or it would ground out and keep the points from working.
Steve found a plastic drink cup on the side of the road, trimmed it into an insulator, and used a little electrical tape to hold it in place. Then he reset the points gap.
Back on the Road to Maggie Valley
Once the gap was set, the cover went back over the points and Steve kicked the Knucklehead back to life. We eased onto the interstate with about 75 miles left to Maggie Valley.
Believe it or not, the bike ran fine all the way there. It just goes to show that with a little ingenuity, tools, and a few spare parts, an old bike can often be repaired in a jam.
Try doing that with a modern Twin Cam or Evolution.
Explore more in Vintage Tech, the Knucklehead Reference, and the Panhead Reference.
Frequently Asked Questions
What does the rubbing block do on ignition points?
It rides on the cam and opens and closes the points to control spark timing.
Can a broken rubbing block cause no spark?
Yes. If the points stay closed, the ignition system may stop producing spark.
Was this a permanent repair?
No. It was an emergency roadside fix intended to get the motorcycle back on the road.
Why carry tools on an old motorcycle?
Because many small failures can still be repaired roadside with tools, spares, and ingenuity.