Knucklehead Ignition Points Roadside Repair | Broken Rubbing Block Fix | Riding Vintage

Knucklehead Ignition Points Roadside Repair

This roadside Knucklehead ignition points repair is exactly the kind of real-world old-motorcycle problem that belongs in the Vintage Tech archive: a 1947 Harley that quit on the highway, a broken points rubbing block, and a repair made from whatever was in the saddlebag.

On a cool fall morning, Steve and I left bright and early to head up to the Southern Coalition AMCA Road Run in Maggie Valley, North Carolina. I was riding my 1964 Panhead and Steve was astride his 1947 Knucklehead. We had about 250 miles to ride and wanted to get an early start just in case we ran into any problems.

Steve's 1947 Harley-Davidson Knucklehead on the shoulder after the ignition points failure stopped the ride to Maggie Valley.

Since we did not need to reach Maggie Valley until 5:00, we took our time and rode the first couple of hours on secondary highways, passing through small towns and scenic countryside. Our first gas stop was only 10 miles from the interstate, so we decided to give it a try. It was a Sunday morning and we figured traffic would be light, allowing us to reach Maggie Valley a little earlier than planned.

Finding the No-Spark Problem

After about an hour riding down the interstate, Steve's Knucklehead backfired a couple times and shut off. We rolled over to the shoulder and I unpacked my tool roll as Steve began troubleshooting his motor. After a little poking around, he discovered that the rubbing block on his points had broken off.

In case you are not familiar with how ignition points operate, the rubbing block rides against a rotating cam, which is shaped to allow the opening and closing of the points. Without it, the points stay closed and there is no spark sent to the coil. No spark to the coil means no spark to the plugs. See the diagram below.

The ignition-points rubbing block rides against the rotating cam to open and close the points.

Making a Roadside Rubbing Block Repair

After scratching our heads for a while, I started digging through my saddlebag looking for something that could replace the rubbing block. A quick search yielded a fork terminal from my electrical spare parts bag. Since the rubbing block is attached with a rivet, I thought that we could slide the fork terminal under the rivet and then cut it to the same length as the original rubbing block.

Within a few minutes, Steve had the rest of the original rubbing block removed and we slid the fork terminal under the rivet. A couple good hits with an improvised metal punch on the backside of the rivet tightened the fork terminal down nicely.

A fork terminal from the electrical spares bag was slid under the original rivet to replace the broken rubbing block.

Adjusting the Points

Steve reinstalled the points and made a couple adjustments to the length of the fork terminal until the points could open and close properly.

Steve reinstalled the points and trimmed the fork-terminal rubbing block until the points opened and closed properly.

Making an Insulator from Roadside Scrap

Normally the rubbing block is made of a non-conductive material, so we could not just let the metal fork terminal ride against the cam because it would ground out and keep the points from working. Steve found a plastic drink cup on the side of the road and trimmed it into an insulator. A little electrical tape was used to hold it in place and then he set the points gap.

A plastic drink cup and electrical tape insulated the metal fork terminal so it would not ground against the cam.

Back on the Road to Maggie Valley

Once the gap was set, the cover was placed back over the points and Steve kicked the Knucklehead back to life. We eased back onto the interstate with about 75 miles left to Maggie Valley. Believe it or not, the bike ran fine all the way there.

Just goes to show you that with a little ingenuity, you can fix an old bike in a jam. Try doing that with a modern Twin Cam or Evolution motor.