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Discussion Starter #423 (Edited)
Unless you are going to ride 2-up, I'd shorten the seat by about 6"
I probably won't change the overall length, for two reasons: 1) it wouldn't extend out to the end of the rear wheel, and 2) it would require reworking the frame loop.

I could theoretically fill behind the seat to bring the bumstop forward, like this—



But I think it would be far easier and simultaneously more in keeping with the 1980s zeitgeist I am trying for to simply fill it in with a really thick upholstered section, like these:

 

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Discussion Starter #426
"Simplify, then add lightness." - Colin Chapman

"Perfection is achieved not when there is nothing more to add, but when there is nothing left to take away" - Antoine de Saint-Exupéry

"This project will be complete not when there is nothing more to add, but when there is no parts left to wreck." - Peter Tanshanomi
 

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Discussion Starter #429 (Edited)
Ever since I finished my Honda CL125S project, I've been telling myself to get back to this bike. But frankly, I've felt more than a little paralyzed, not really confident about how to proceed. There's bodywork questions, the footpeg and pedals are all totally up in the air, and I've had a devil of a time getting a precise measurement on the chain offset, since I don't have all the engine mounts sorted yet. There's also the whole engine rebuild I've been putting off. So, this morning before work, I sat down next to the bike and tried to think things through. I decided the biggest bottleneck was nailing down all the measurements needed to make my rear engine mounts. The chain offset is still slightly loosey-goosey, but I've decided that being within a millimeter or two will have to be good enough for now, just so I can stop dithering about it and get back to creating some hard parts. Better to do it and discover its wrong than never get around to doing it. With this in mind, I did design in some adjustment just by changing the length of a couple dowel spacers. The only thing I don't have here is distance from each of the upper and lower crossbars to its corresponding crankcase mounting boss. I already came up with some plastic templates that should be lying around somewhere in my workshop, I just need to find them and measure them.

 

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I love AutoCAD for getting those details right. I designed 2 different monoshock swingarms for Norton Commandos, and they both worked great. (Rising rate, linkages, too)
 

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Discussion Starter #432
I'm continuing to plug away at the rear motor mounts. It took a lot of trial fitting and filing to get the lengths of the inner rods and outer sleeves just right, so that there was no slop, but the rubber mounts didn't get crushed once everything was torqued down.

Now I am working out the dimensions of the actual mounting tabs between the assembly and the engine bosses with some scraps of HDPE sheet.

 

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Discussion Starter #433
And here are the upper tabs in 1/4" steel. I didn't cut these myself; I found a place not too far away who can laser-cut parts from a DWG file. I e-mailed the file, PayPal'd them the money, and a couple of days later these showed up in the mail.

They still need to be welded. I haven't decided if I want to do that myself or have my local welding pro do it. I designed them to be captive on the cross-tube, so it's not a structurally critical weld, but these will be really apparent, and I don't want it all to look booger-y.

 

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Discussion Starter #434
So, I haven't bothered to make a build thread for it on here, but I have another project bike in the works alongside Bultakenstein. I've always wanted an Aermacchi/Sprint 350, but parts are scarce and they're just finicky enough that I just can't see myself going down that rabbit hole. Separately, I've also always wanted to turn a Ducati engine into a horizontal single, à la the Supermono. When I was offered a bare '73 Harley SS-350 frame for the cost of shipping ($150), I thought, why not combine the two ideas? Would a Ducati Monster engine, minus the rear pot, fit in there? I did a quick Photoshop visualization, scaled as accurately as I could determine, and it looked as though it might actually work.
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I went ahead and bought the frame. Once it arrived, I picked up a damaged set of empty Duc crankcases, and a left-side SS-350 case half. Amazingly, the engines are very similar in size. In this photo, the output shaft openings are aligned:
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At this point, I've grafted Suzuki forks and 17" wheels onto it, and started playing around with engine placement. So far, I don't see any need for permanent modifications to the frame or to the engine. The forks I already had (purchased by mistake for Bultakenstein), the front wheel is from a 400 Bandit, and the rear is a 600 Katana. I swapped out the sprocket carrier for one from a GS500, and the chain run looks close to spot-on. I put some cheap IRC rubber on the wheels just to keep them from getting damaged, and so I'd have a rolling chassis.
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The only thing I'm pretty intimiated by will be fabricating the Supermono-style counterblancer assembly. I wouldn't try to fabricate the parts, I would probably just have them professionally fabricated. Fortunatley, there's a "Ducati Supermono Replicas" FB group, which has lots of examples people have already made. Here's a photo I stole from there:
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So, anyway, that's what's up. It really has not impacted Bultakenstein's progress, as far as I can tell. If anything, it's helping motivate me to get down in the basement and get busy!
 

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Cool Norcati!

The Knucklehead 'Macchi is a great little bike, they race them in AHRMA. Specifically "Doc Z" who builds and sells Solo roller starters is one of them; I traded him a 350SX engine for a set of rollers. I think I gave away the rolling chassis...
 

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Discussion Starter #437

Since the Bandit 400 front wheel I got for the Aermacchi-Ducati Special is interchangeable with Bultakenstein's 19-inch cross-spoke wheel (same axle diameter and fork width), I tried swapping front wheels between the two project bikes, just to see how they'd each look.

Initially, I thought the 17-incher looked great on the Bul, and briefly considered switching them out. However, the cross-spoke didn't do as much for me on the other bike, and lots of problems arose with the rear wheels:
  • Even with the GS500 sprocket carrier, the Katana 600 hub is too wide on the chain side to center properly in Bultakenstein's narrower swingarm without serious modification. The Aermacchi swingarm is stupid wide for some reason, and has plenty of room.
  • The disc rear will require a master cylinder mount, which would add yet another task for the project I am trying to finish first.
  • The sprocket offset is pretty damn close on both bikes as they are now. Swapping the wheels would screw them both up drastically.
  • I've already ensured that Bultakenstein's steering geometry has suitable trail. I'd have to do that all over again.
Aesthetically, I decided the tri-spoke wheels and wider tires are too modern for Bultakenstein. I really want it to look like something some guy might plausibility have built in his garage in the mid 80s.

So it was an interesting diversion, but in the end, each set of wheels will stay on the project for which they were originally purchased.
 

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Discussion Starter #438 (Edited)
You know the old saying, "Measure twice, cut once?" Of course you do; it's a well-known saying for a reason.

Even though I started by making up a hardboard template first, my first set of tabs for Bultakenstein's lower engine mounts mysteriously ended up 1.5mm short. And, of course, I cut both of them before checking the fit.
Fortunately, my second set, shown on the right, are spot-on.

The motor mounts finally went to the welder today (responsibly dropped off in a ziplock baggie at his garage door), which has me very excited. This was a long time in coming. The tabs will be spaced out further than shown in these photos, with some spacers that can be fine-tuned later if necessary, to ensure the countershaft sprocket is perfectly aligned to the chain run.

 

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Discussion Starter #439
Well, my rear motor mounts are done! It's been a long time in coming, and feels fairly momentous: for the first time in 8-1/2 years, I have the crankcases, the wheels, and suspension all solidly bolted to the frame. Just as importantly, the alignment of the engine is spot-on.

Compared to Bultaco's original method of mounting the engine, mine is much heavier, more complex, and probably not much more rigid. To be fair, I should point out that my arrangement—unlike the original mount—also turned out very nearly un-assemble-able (well, at least without removing the swingarm). Fortunately, I found out that I could, indeed, get all the bolts slipped into place by orienting everything just so, and following a specific order of assembly.

I still have to make the spacers for the lower rear mounting bolt, as well as source proper hardware to replace the mismatched collection of bolts I have now, but that's minor stuff. The big, blurry question about how to mount the engine has been answered.

And all of this was so that I could use a monoshock swingarm—something I have long since abandoned! I'm curious how much effect rubber mounting the rear of the engine will actually have, considering that the upper and lower front mounts are still solidly bolted to the frame. At this point, I mostly hope it won't have any unintended negative consequences. But I'm done worrying about how good this bike will be. I made lots and lots of ill-considered decisions early on, because I didn't know better. (It's amazing how much quicker, easier, and better the Aermacchi is going together, now that I have a lot more knowledge, plus the proper tools and equipment.)
 

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Discussion Starter #440
With the counter shaft sprocket solidly in place, I could now get an accurate measurement of my sprocket alignment. The drive sprocket and rear wheel sprocket are less than 1/4" out of line. Basically, the width of a sprocket (0.227"). The inside edge of the rear sprocket aligns with the outside of the front sprocket, so I will need to put the sprocket carrier in the lathe and take a bit off the face of it.



 
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