Project Car SOTU: Bultakenstein & The Honda CL125S

Over the years that I’ve been dabbling with my project Bultaco, a certain annual rhythm has evolved. Around the middle of November, my workshop time erodes as my spare time and money starts getting earmarked for holiday get-togethers and Christmas shopping. Once the holidays are over and the credit cards are paid off, usually sometime in February, I rededicate my free moments to project tasks again until mid-summer, when vacation trips (not to mention really, really nice Spyder riding) distract me again. There’s another less intense, shorter period of activity in the fall until things grind to a halt for the holidays once more. Things have been going this way with Bultakenstein since 2011, and I have a fairly complete, rolling, homemade chassis to show for it, along with most of the parts needed to assemble a working engine. This year, things didn’t work that way.
As you may recall from my last Project Car SOTU update, I picked up a ’74 Honda CL125S a year ago. It was intended to be a fun commuter/neighborhood runner to keep me on two wheels and assuage my growing discontent with the glacial pace of Bultakenstein’s progress. Well, a year later, neither two-wheeler is on the road, I’m buried in work at the office, I’ve spent forever helping edit my father’s latest book, and the Bultaco is mouldering in the workshop, unattenteded to. The situation is not all that sad, however. Even though the CL125S has become an unintentional second project, I have completed some fun and rewarding work on the little Honda.

The Honda CL125S

The three big tasks I had to get the Honda roadworthy were 1) resolve some titling issues, 2) repair the rotted-out exhaust, and 3) seal the rusted-through fuel tank. The first one took more than half the year to resolve. Naturally, I was hesistant about spending too much time and money on repairs until I was sure the bike could be legally registered. Fortunately, I now I have a valid Missouri title in my name—one down, two to go. Once I had the paperwork issues cleared up, I moved on to the exhaust.

I briefly toyed with the idea of welding up the rot in the extremely cool-looking stock exhaust, but the more I got into it, the more apparent it became that the original muffler was beyond saving. Since this was never intended to be anything but a low-budget runner, I opted to create my own replacement muffler on the cheap. Unfortunately, the OD of the stock exhaust pipe is only 1.25″. The only thing available in that inlet diameter is a universal SuperTrapp exhaust that would have been tough to fit, and was also way outside this project’s fundosphere. Instead, I bought a cheap oval canister muffler and bracket directly from Hong Kong for $40 shipped, via E-bay. It had a 1.5″ inlet diameter, which would require an adapter of some type. To complicate things, the stock muffler body extended well forward, welded to the headpipe just behind the footpegs. Once I lopped it off, I had only a stubby little pipe to work with. To resolve both of these issues, I bought a length of 1.5″ OD, 0.125″ wall pipe which provided, by computation, a 1.25″ ID. Well, nominal measurements being what they are, the pipe didn’t quite fit onto the truncated original exhaust system, but thanks to the unbridled awesomosity of owning a lathe, I was able to chuck it up and easily bore the ID on one end so that it was a snug slip fit over the headpipe. I then drilled and tapped the muffler and my new pipe for three setscrews each, and bingo, my exhaust was coming together.
I now needed a heat shield. I picked up a length of larger diameter stainless steel pipe that I crafted into the stylish, shiny shield shown in the lede photo. Not only will it keep the rider’s leg from burning, it neatly hides the joint between the original headpipe and the extension. I fabricated two alloy rings on the lathe with two different IDs that slid snugly over the header pipe and extension pipe respectively, but the same OD, which matched the shield’s inner curvature. (Again, owning a lathe is beyond awesome.) More setscrews, and we’re almost done. The only tasks left are fabricating the hanger bracket, as you can see from the zip-tie in the photo, and hitting the header and extension with high-temp flat-black paint. You can see in the lede photo where I used some high-heat JB Weld to fill and smooth out some pitting and corrosion further up on the headpipe where the original heat shield was clamped on.
The second task is the tank. I stripped the paint and corrosion off it, then attempted to solder up the pinholes. My initial attempt was a failure, but thanks to some helpful online forum members, I eventually got the right solder, the right flux, and the right technique. I have also ordered a Caswell tank liner kit, which will probably be applied to the inside of the tank sometime this week. I have a bunch of Ford Engine Blue rattle can paint to use up, so that will be the color of the tank and side covers when I’m done. I did buy a white vinyl racing stripe to class it up a bit.

One lower-priority item was to replace the faulty speedometer. Sadly, the correct speedo is extremely rare and very, very pricey. I wanted to keep the period feel of the bike, as seen from the cockpit, so I was disappointed by the prospect of a modern aftermarket gauge.  Fortunately, E-bay came through again, and I was able to score a slightly different speedo from an earlier CL100 for only $18. I have yet to verify it works properly, but if it is anywhere near accurate, it will be a major score.


Naturally, all this effort on the CL125S has come at the expense of Bultakenstein. It’s not much changed since I last reported on it. The only additions have been a new front fender, off a Honda Nighthawk 650, and a brake caliper for the Suzuki front end. The next task looming before me is properly mounting the rear of the engine, since the frame has nowhere to attach it. The original Bultaco arrangement was a bracket that fit into a gap in the center of the swingarm, affixed to the swingarm pivot shaft. Not only does my Yamaha swingarm not have a suitable gap, but it also uses a 2 mm smaller diameter pivot bolt which probably shouldn’t be subjected to the extra stress. So, I must weld in two frame tubes—one above the engine, one below—that I can attach mounting brackets to. One of the reasons why I’m reluctant to get back into it is that the whole thing has to be disassembled for me to weld in the cross-tubes, and I emotionally fear that I will somehow be losing ground when it goes from a roller back into just a pile of parts. It at least looks like a motorcycle now.

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  1. dead_elvis Avatar

    Possibly my favorite of all these excellent(!) PCSOTU posts.
    How well do heat shields like that, original or not, really work?

    1. Tanshanomi Avatar

      They are the difference between, “Oops, that was briefly uncomfortable,” and “Oops, my leg has no skin on it.”

      1. dead_elvis Avatar

        About what I figured, and another point in favor of ATGATT.

  2. I_Borgward Avatar

    That’s a damn nice looking heat shield! And, while I am envious of both the lathe and drill press, that console TV workbench is just too cool.

    1. Tanshanomi Avatar

      It is the solidest piece of cabinet-making I have ever seen. A neighbor down the street my wife grew up on put out at the curb in 1969, so it probably dates from the 50’s.