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Budget Parts-Bin Bultaco

This is a discussion on Budget Parts-Bin Bultaco within the Project Builds forums, part of the Caferacer.net Forums category; quote: Originally posted by Kurlon Rather than a pair of washers on the right, why not another spacer like the left. 12mm ID through out, ...

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Thread: Budget Parts-Bin Bultaco

  1. #11
    Senior Member Tanshanomi's Avatar
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    quote:Originally posted by Kurlon

    Rather than a pair of washers on the right, why not another spacer like the left. 12mm ID through out, say 20mm OD, necked down to 14.5mm (or bigger if you're up for reaming the frame anyways) OD to pass through the frame. Reinforce the frame with a new washer on the outside with the ID set to match the OD where it passes through, trim the necked down portion of the spacer so the nut seats against the new washer before running out of thread or hanging up on the spacer? That way you don't have that small void that is currently present between the washers.
    I get it. Makes perfect sense, great suggestion. That's exactly the sort of help I was hoping to get on this forum.

    Hopefully people will find it useful and interesting to see all the iterations, changes and blind alleys I go through in thinking through this build.

  2. #12
    Senior Member Tanshanomi's Avatar
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    I have not done much work on the bike other than lots of measuring and test-fitting, but here's an update.

    I revised my swingarm arrangement thanks to Kurlon's suggestion. A new swingarm bush arrived and the good news is that the threads on the Suzuki axle fit inside the bush no problem, so this will work. So, here's a third "no weld" version (I probably will still weld the red washer to the frame, but that will be only for secondary support).



    If I can figure out exactly where the swingarm needs to be located to center the back wheel this evening, I'll drop the pivot bolt off with a retired machinist I know tomorrow morning and have him turn it and make up the spacers. In related news, I really, really want a lathe.

    I also fitted up the forks and a rear shock to the bike temporarily and mocked up this illustration. The shock is an XR100 unit, which won't be the final component, but it provides an idea of what length I need (it's 10.5") and gives me some something to work with for right now. The forks are a bit long, but I am planning to use clip-ons mounted above the top triple clamp, so hopefully I can make them work without further modification.



    If you want to see the raw photo, without the tweaks, it's here: http://www.tanshanomi.com/project-x/PB030031.JPG
    Last edited by Tanshanomi; 12-26-2012 at 10:56 AM.

  3. #13
    Senior Member Tanshanomi's Avatar
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    The forks are from a Suzuki GS650L cruiser. I was originally looking for a set of standard GS450 or 550E forks, because I thought the leading-axle design used on the "L" moddels would look too "cruiser-ish" for the sporty look I'm after. But when I found these locally for $65, including the steering stem and trees, I couldn't pass them up. Then I recalled plenty of standards and sports bikes had leading-axle forks back in the day: Ducati GT, Royal Enfield Interceptor, /5/6/7 BMWs, the KZ1000ST... and then it occurred to me that leading-axle forks were the PERFECT choice for this bike. Why? Well, because...

    Last edited by Tanshanomi; 12-26-2012 at 10:56 AM.

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  5. #14
    Senior Member Tanshanomi's Avatar
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    Okay, so I've not made a lot of recognizable progress, but I have been picking up more parts, as well as doing lots of measuring and head-scratching.

    After thinking things through more, I've chucked the whole idea I originally had for mounting the swingarm. I just didn't like the idea of relying on a 9-1/2" x 12mm bolt to support both the swingarm pivot and the rear engine mount, with nothing else tying the rear of the frame cradles together. But thanks to my random selection of the YZ swingarm, I'm limited to that pivot bolt diameter unless I either start hacking up the swingarm or toss it and start over with another style of swingarm. I'm not real keen on either of those options at this point. Not to mention that I'd be out the $72.95 I've spent on new swingarm bolt, bushings, shims and seals!

    So instead, I've decided to divorce the pivot bolt function from the frame cross-bolt and rear engine mount, as shown (this is a plan view from above):



    In order for the the swingarm bolt to clear the lower frame cradle during insertion and removal, It will have to move back a little more than 2-1/2". That will increase the wheelbase that amount, which might help the ride and stability a bit (who knows how this thing will handle!) as well as give me a little more room for a longer rear damper unit.

    I bought a length of 0.156-wall 7/8" DOM tubing and cut it to fit between the frame plates. Yea, that's a bit heavy, but with the swingarm cantilevered out that far, it'll potentially exert some serious torsional forces on that tube. Additionally, the tube ID conveniently matches the 14mm existing mounting holes in the frame side plates. I also bought a piece of 3/8" flat stock that I'm going to make the axle mounting plates from (the blue pieces in the diagram). Even though 3/8" plate steel feels massive, I could put in some gussets (shown as dotted blue lines). I'm interested in people's feedback on whether that's necessary.

    There's no way my little 110 MIG welder will get decent penetration on .375 plates (or even .156 tube) but I should be able to tack weld it together and then take it to a "real" weldor to make it all solid. I haven't decided if the cross tube and drive-side plate should be welded to the frame. The whole assembly could conceivably just bolt in place, since the rear engine mounting plate(s) would prevent the assembly from rotating (once I determine what engine I'll be using!)
    Last edited by Tanshanomi; 12-26-2012 at 10:56 AM.

  6. #15
    Senior Member Tanshanomi's Avatar
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    I haven't updated this in several months, mainly because I haven't progressed enough to have anything new to show. I decided that I definitely want to go with a Bultaco engine, for several reasons: 1) I like Bultacos. I've owned three of them, and they're great motors. 2) I know Bultacos (See Point #1). 3) Any other motor would require additional frame modification, and thus time and expense. 4) I would like the finished product to be "a Bultaco" rather than a mongrel combination of engine and frame. That might also help me get a street title for this bike.

    So I've slowed down while looking around for just the right Bul motor. Even though any Bul 5-speed engine will fit my frame, they're not all identical. I am being a bit picky about the particular model I go with. In keeping with the budget aspect, the asking prices for complete Bultaco motors vary widely. I would rather bide my time and find something that's not at the top of the price range.

    In the meantime, I bought a set dummy set of Bultaco engine cases to use while making up the swingarm pivot. I also bought a stock rear engine mounting bracket, which will require me to either cut the engine mounting tube in half, or bore a hole in the engine bracket the OD of the tube. Not sure which way I am going to go at this point, but I've definitely reined in (or perhaps restricted) my options a lot by settling on an engine design.

  7. #16
    Senior Member Tanshanomi's Avatar
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    I thought the XR100 shock was a bit dinky-looking, and I knew it wouldn't have the spring-rate or damping to handle the bike's mass. So I scored a rear shock from a Kaw ZX-7 on the cheap. I knew it would be total overkill, but I figured I'd rather have a near-hardtail than something bottoming out all the time.

    Holy Schmoly, the thing is the size of a small pony. It's a waste of $17 as far as this project is concerned, but as a paperweight it'll sure hold down a lot of paper on my desk.

  8. #17
    Senior Member Tanshanomi's Avatar
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    Just as an update, I haven't abandoned this project or anything, I'm still slowly collecting parts and fitting them together. As I said when I started this thread, it is going to be a very slow process, since I am trying to do this in my spare time at minimal cost. The overwhelming issue (other than a lack of free time) is that everything affects everything else, and I am REALLY trying to think through all the steps in order to not waste resources on fabbing something in such a way that it doesn't work down the line.

    Also, I am trying to fabricate/modify stuff without spending too much on tools. For example, I devised all sorts of cunning ways to accurately and easily enlarge the rear wheel slots in the swingarm by the required 2 MM, but in the end I just carefully used a Dremel tool. It was time consuming, and could have potentially screwed up my swingarm, but it cost me nothing to do.

    I'll try to post some pictures of my progress soon, if anybody still cares.

  9. #18
    Senior Member Tanshanomi's Avatar
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    Just as an update, I haven't abandoned this project or anything, I'm still slowly collecting parts and fitting them together. As I said when I started this thread, it is going to be a very slow process, since I am trying to do this in my spare time at minimal cost. The overwhelming issue (other than a lack of free time) is that everything affects everything else, and I am REALLY trying to think through all the steps in order to not waste resources on fabbing something in such a way that it doesn't work down the line.

    Also, I am trying to fabricate/modify stuff without spending too much on tools. For example, I devised all sorts of cunning ways to accurately and easily enlarge the rear wheel slots in the swingarm by the required 2 MM, but in the end I just carefully used a Dremel tool. It was time consuming, and could have potentially screwed up my swingarm, but it cost me nothing to do.

    I'll try to post some pictures of my progress soon, if anybody still cares.

  10. #19
    Senior Member Tanshanomi's Avatar
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    I've been too lazy to take photos of my progress, but I now have enough parts that I need to stop collecting and start making them all work together. But this is definitely a "back burner" project, and I've only been able to devote a couple of hours a week to it. I'm starting to get a clear picture of the enormity of the task. Every step in trying to make a motorcycle out of junk takes more effort and expense than you can predict.

    For example, take a look at my cylinder.

    I found a jug from a 200cc Bultaco Model 45 recently on Ebay. Despite the seller's assurance that "ALL FINS ARE GOOD," I was disappointed to discover once it arrived that the bottom fin was bent on the
    left-hand side. I got it for under $150 (incl. shipping), so it still isn't necessarily a bad deal ...but it's not the killer deal I thought it was, and it has added one more thing to my list of to-dos.

    Can this be straightened, and if so, what's the proper technique? So far I've been told to heat it with an oxy torch, to only use a somewhat lower heat such as propane, to heat it to about 500 degrees by putting it in an oven, to NEVER try to heat cast iron...simply bend it very, very slowly with light taps on a wooden wedge between the fins.

    Or am I just tempting disaster if I try to fix it? If it's too risky, I'd rather have a bent fin than a broken off fin, I guess, but I'm kind of bummed about the appearance. It's an otherwise good barrel.


  11. #20
    Moderator joe c's Avatar
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    come on....someone here knows the answer....



    not a pretty boy honda rider... i\'m fag on a TTR

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