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It turned out well for the first effort and new tools. You need to be looking for faults to find them, nothing jumps out. You are more critical because you know where to look.
 

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Discussion Starter #583
Finished upholstering the seat. My stitch lines are a bit haphazard and the fit is slightly wonky in spots, but I'm not too disappointed. It'll be a perfectly serviceable part, and not horrible looking for my first shot at doing this sort of thing. Now on to fabricating brackets to bolt it to the frame.

 

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Discussion Starter #584
I was about to bend stock into brackets to hold the seat, when a light bulb went on. I would basically be recreating single-hole conduit clamps, so why not just buy some of those?


Meanwhile in other news, I started work on my revised steering clamps. I'd previously bought a GS500 triple clamp for one of my other projects [The Aermacchi-Ducati Special]. With just a tiny bit of mathing, I discovered that the GS steering stem is the proper length to fit the Bultaco frame without the kludgy spacer I'm currently using, and without turning down the steering stem. Unfortunately, the GS500 has larger fork tubes and the wrong clamp offset, so the triple clamps are not suitable. Therefore, I bought two additional steering stem/lower clamp assemblies: one GS500, one from a GS650L (what Bultakenstein uses). I ground away the welds on the bottom of the stem on each and pressed them out.

As i suspected, they have identical diameters at the bottom. After a quick swippity-swappo, a quick trip to my friendly neighborhood welder is all that's needed to have a GS650L lower steering clamp wedded to the shorter GS500 stem.

Perfect! Oh, no...wait. The GS650L top clamp doesn't bolt to the other end GS500 stem. I ended up cutting apart a spare adjustment nut to make a threaded collar, and then turned a stepped alloy spacer to make a cap nut.

The whole stack goes together like this, and another sticky issue resolved.

Bultakenstein's existing steering stem won't go to waste. It will get used on yet another project I've come up with, mostly to use up a lot of Bultakenstein's rejected parts.
 

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Discussion Starter #585
I mounted the seat this morning. Nothing very high tech, but still a minor milestone.
I hit the conduit clamps with some dark gray paint to make them less noticeable, then I glued strips of 3mm neoprene inside them to give them a snug fit and protect the frame once it gets painted.

I initially tried attaching the clamps to the plastic seat base with self-tapping screws, but that was clearly the wrong way to go. So, I disassembled the seat shell from the base and installed rivnuts into the seat base from above. Even though they're intended for metal plate, they expanded out into the HDPE base material nicely. I could then use 6mm bolts to snug everything up from underneath.

The weight of the seat sits on four plastic furniture feet to protect both the frame and the seat cover snaps.
 

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Discussion Starter #586 (Edited)
The revised steering stem setup is coming along nicely. The GS500E steering stem is a snug slip fit into the GS650L lower triple clamp. I mocked everything up, and I just needed to make a couple of tweaks to get it set up.

The bearing-to-bearing distance in the frame is just slightly short for the stem (just a few millimeters). So, I chucked up the stem in the lathe and extended the diameter where the upper bearing fits further down the shaft a bit, to ensure the bearing has room to float once everything was properly adjusted. I also had to undercut the area at the end of the threads, so the nut won't bottom out, and can travel past the end of the threads slightly if needed. (No criticism of the turned surface, please. I bought some new carbide tool tips off Amazon and they are utter crap.)

I was more liberal with the increased travel than I needed to be—about half the thickness of the bearing—but there's really no functional downside to that. One reason I did this was that I mocked up the fit using a plastic analog in place of the bottom bearing. I didn't want to press the bearing on yet, since the stem has to be welded up first, and I also need to make a steering stop adapter that will have to go on the shaft first. I made this HDPE as close as I could to the correct dimensions, but inaccuracies creep in when you do things like this. It would be a total bummer to get the whole thing welded up (at which point I won't be able to fit the stem in my 8" lathe), and then discover at that point I didn't take enough off.

Next step is to re-weld the stem to the lower clamp. I will be dropping the assembled forks by my local welder this afternoon, and he should have the job done within the week.
 
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