There are quite a few neat old headlamps upstairs in the shop just wasting away. So when I came across this one, which came off of a 61 Triumph Pre-Unit chop, and saw how nicely the shape of the lens and body fit the language of the Scotchster build, using it was a no brainer. The only issue was the output of the original bulb and by that I mean lack of output.
The objective here was to maintain the basic look and function of the headlamp, but give it an easy to replace, high output lamp element with a lifespan that was measurable in more than hours. Because light bulbs on bikes take lot of abuse, the ever present H-4 Halogen type insert seemed like a natural choice. They are very bright, durable and readily available. However, even though the H-4 bulb is pretty small, the bulb and socket combination is a bit larger than what the “stock” housing was designed to facilitate, so this project will require fabricating a small addition on the backside of the headlight housing.
The first step in this project was to make the adapter. I needed something to hold and locate the H-4 insert on the backside of the reflector. After measuring up the H-4, I found a section of aluminum tube that was close to the size I wanted, chucked it up in the lathe and bored it out until the ID of the tube allowed the H-4 to drop into it.
Then, since the H-4 bulbs come with tabs that protrude from its circular base and these tabs are normally used to locate the insert in its housing, after a little math, layout fluid and milling, I was able to use them for the same purpose. So now we have one side of the adapter that is milled for the location tabs, and also drilled and tapped for two 4-40 thread pitch screws, so the insert can be bolted down and locked into place.
The opposite face of the adapter needed a place that allowed the headlight reflector to attach. Measuring the overall outside diameter of the glass on the H-4 bulb itself, and finding that it was very close to the size of the hole in the reflector, meant I was able to re-use all the holes already in the reflector. All I had to do was open up the ID of the center hole in the reflector a tiny bit so the new H-4 could fit through it, and make a matching mounting hole pattern on the adapter.
( I opened up the center hole with a die grinder very slowly, for fear a drill bit might break through into one of the smaller mounting holes around the center hole and/or catch and ruin the sheet metal reflector.)
To make this part, I cut out a circle in some thick aluminum sheet metal and welded the circular cap onto the adapter. Then using math and stuff again, laid out the hole pattern. The three small holes around the center hole are drilled and tapped 4-40, and the middle hole is just large enough for the glass part of the H-4 bulb to pass through.
When the bulb and adaptor are bolted together it looks like this:
And when he whole assembly is bolted together it looks like this:
So now that the H-4 Insert adapter was made, and it effectively married the H-4 bulb to the OG headlight reflector, the next step was to enclose the back of the headlight bucket around the H-4 socket, and try and make it look good too.
To do that, I used a couple sections of exhaust tubing and a bit of sheet metal.
After making a set of mounting ears to mount the headlight assembly on the Buell front end being used for this build, the end result is a pretty rad, "recycled” headlight!
So now that we have a headlight and mounts that are going to do what we want them to, they can go out for final finishing, which in this case will be powder-coating.
If you’re curious to see how it all comes out, keep your eyes out for photos of the Scotchster Build when it’s all done!