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Project: building a super bol d'or

Discussion in 'Modifications and Projects' at netrider.net.au started by bikeboy, Jul 29, 2009.

  1. The project: upgrade frame and suspension on a 1981 CB900FA.

    I've picked up a donor bike to work on while I still ride my 'stocker' around. At the end of this project, I should have 2 CB900s with very differnt characteristics. The plan is to rebuild everything on the "super bol d'or" to take advantage of various technical advances in the nearly 30 years since it was new. Looking forward to the radial tyre experience ;-)

    I rushed into ebay a bit, and ended up with a front end of a "hurricane"-which was an F1 but they didn't know it yet ;-).

    Anyway, they had w weird anti-dive brake set up I didn't want, so they went down the back shed. Along with the three-spoke rim I thought looked OK at the time. Right beside the 16" VFR boomerang comstar I also thought was a good idea. In fairness tho', I got it with the rear wheel, which increased my tyre width from a 140 to a 170. I have a win every now-and-then, just to keep me interested :)



    Back to ebay, and look for F2 parts.For no particular reason, the first thing I tackled was the front end. A common and reasonably straight-forward conversion is to graft a cbr600 forks and clamps to the 900 steering stem. This involves little more than removing the stem from the 900 clamp, and pressing it in to a 600 lower clamp, with a 10mm spacer underneath to compensate for the different casting thickness.


    From there, you just fit the assembly as usual, and insert the 600 forks, axle, spacers, wheel, rotors and calipers. Bingo bango-instant cbr front-end.


    All good so far. But. Along the way I've collected a cbr900 front end, and apart from the stupid 16" front wheel, I'm thinking I'd like to try that instead-primarily because of the 4-piston brake calipers. I'm going to test the 17" wheel and rotors in the 900 forks to see if that's an option.


    Any way, I've also been thinking about the rear end, and have a couple of options there too. First idea was to fit (another)cbr660 (rear) wheel into an 1100 swing arm. Again it's a fairly common swap, and pretty simple. Some fiddling required to centre the wheel and align the chain, but nothing too taxing. The trickiest part is fabricating a brake-stay mechanism for the rear caliper, but it's not rocket science.this is where we get to with this set up:


    As with the front, I'm starting to consider a more radical solution ;-)

    The plan now is to transplant the complet rear end from the cbr onto my cb frame. This of course means going mono-shock, and the conversions I've seen look really sick.


    There are 2 schools of thought regarding the process, and I'm procrastinating at the moment. The problem is that the 900 has a 16mm pivot bolt, and the 600 uses a 15mm bolt. The spacing is off by 3mm each side too, but that's not hard to rectify.One method is to remove the pivot housings from both units, and weld the 900 on the 600 one. This method retains the 900 pivot bolt and spacing, as well as not having to modify the rearset mounts, which the bolt passes through. To this end I've made up a jig that will hold the 900 pivot in place, and give me the correct alignment for the 600 arm.


    and with a bit of patience, it should turn out something like this one (not mine):


    The second option is to replace the 15mm ID ball races in one side of the 600 unit with some with a 16mm ID. I have these already, and they fit the 900 pivot bolt perfectly. I would also need to get the 600 pivot bushes bored/machined out from 15mm to 16mm, but that shouldn't be too hard. After that, I'd just need two 3mm spacers either side of the arm.

    The suspension of course is going to be where most of the work is. More to come...

  2. This looks like a really cool project! Look forward to watching the progress.

    How much of an engine over-haul are you going to do? I'm guessing bottom ends and all the horrible stuff could be getting cranky on some of these by now....?
  3. thanks :wink: As for the motor-it's already in bits. I suspected some 'nastiness' when I spotted the silicone weeping from the crankcase joints :cry: Sure enough, there were snakes everywhere. Concentrated around the oil pickup naturally enough:

    Surprisingly, the bearings looked serviceable, but will be replaced anyway. I plan on a wieseco big bore kit. Crank will be OK with a linish. I have all the new chains and guides here already, and I'll clean the head up and replace the exhaust valves. Intakes are OK, but will lap them anyway. Guides are in spec. I can take my time with this, so I might as well.

  4. Mate, my mechanical skills don't stretch beyond basic services, touching wires togther, and poking the funny things inside the carb! Wish I had your ability - there are so many great older bikes which could be made into fantastic rides all over again with the know-how, but paying somebody else makes it so prohibitve that they sit and rot instead.

    Met for the second time last night with a guy who did a similar thing with a '79 SR500, though he wasn't aiming to update like you are doing, but to get showroom stock condition. It's a fantastic thing to see old bikes getting a second lease! I find them so much more interesting than so much that's on the showroom.
  5. Yeah, I've done the 'restoration' thing to my daily rider, and really enjoy riding that around. It's the usual story - had one when they were new, regretted selling it- yadda yadda yadda - just happened to come a cross a bargain etc :wink: If you have some spare time, you can read a bit of the story here

    Rather than do a second one, I thought I'd go down a different path.

  6. Good project. I will be watching with interest.

    It's hard to imagine the bearing bores being correctly aligned with a cut and weld swingarm pivot as above. To get proper alignment you would need to bore it again anyway.

    So you may be better off with careful bearing/shaft selection, rather than cut and weld.
  7. Are you suggesting the pivot may distort during the heat cycles? I hadn't considered that? If I insert and tighten the bolt during the process do you think that would help?

    Thanks for the input.

  8. It may help, but you could end up bending the pivot shaft. Welding a channel or couple of bars on opposite side, welding the swingarm, then grinding off the temp brace may get it closer.

    Someone with more welding experience may be able to advise.
  9. Cool. I'll keep it in mind. Having my brother do the welding. He welds steel boats together :wink:

  10. update

    Well, I've had a bit of a re-think, and it decided to keep the swing arm complete, and change the bearings and sleeves to use my pivot bolt. Less stuffing around in the end. I've stripped and painted the frame a temporary flat-black, but it's more like a really low sheen satin. I like it a lot, and I'm going to see if my powdercoater has something similar. It will really fit the scheme I have in mind :wink:

    Anyway, I mocked up the rear today after re-furbing the shock:

    I need to get some round stock and some plate for the top mount, because the yellow rope clashes :wink:

  11. Good stuff, I love to see these older machines restored/modified. We have had so many great machines (and several not so great) through the years.
    The new gear handles better, goes harder and actually stops when you wish it to, but unless you have unlimited licence points and money, we cannot utilise these attributes totally except on a track.
    Keep up the good work (and a photo now and again please).
  12. I would be wary of changing geometry at all, but to each their own, many people have had success fitting wider wheels and so on to classic bikes.

    Cosmetically, go hardcore 80's endurance racer replica imo.


  13. Reports from other guys that have done similar conversions say handling is much improved, with quicker turn-in due in most part to slightly lower front end. Improvements gained by running radial rubber seem to far out-weigh any frame 'voodoo' anticipated. I've fitted the widest rims I can get (economically), but still can't get it wide enough for radials. There's a company in the states that widens comstars, but they want US$500 a wheel.

    There's some nice tricky bits on those endurance races isn't there? Don't see much of that come up too often.

  14. Interesting stuff. Good luck with it.
  15. Well, some baby steps. I've taken the 600 swingarm spacers in to a local engineering firm, and they don't see any problems boring them out to take the 16mm bolt. They were to have them finished this arvo, but the bloke that was to do them forgot :cry:

    In the meantime, the 900RR lower triple has arrived, so I removed the stem and inserted (another) 900 unit in, along with a new bearing. This meant I could test fit the 900RR forks and test my 600 wheel/RR brakes theory:


    The good new is it's going to work :wink: I'll need to measure and fabricate a couple of spacers for each side, but the wheel and discs will centre nicely under the 900 calipers. I'm still waiting on the top clamp, and some handlebar risers which will mean I can drop the forks down as far as they'll go to compensate for their shorter length. I can't measure the spacers until I know the forks are parallel.
  16. All the best with the project Bikeboy

    And is there a drooling smilie for the pics from KK :cool:
  17. boring

    Well, I got the bushes/spacers back from the engineering mob. Look pretty damn good too. Although they did run into an 'issue' with the hardened bearing sleeve. I suspected it was hardened, but forgot to tell them, and it took 90 minutes to sneak up on the 16mm with the boring bar. Oh well, got there in the end, although the quote took a hit :cry:


    That's the culprit on the left. Nice and shiny but.
  18. spacing

    Got the spacers back from fabrication too. All up I need 6.5 mm both sides.


    The larger one is to replace the original, with the 6.5 mm added. Seems neater than piggy-backing 2.
  19. beautiful bike
  20. steering

    Got my risers and a pair of handlebars ready. Need to drill the top triple to accept the risers. My measurements suggest the 'bars won't interfere with the adjusters on top of the forks (still have to figure out what they do!!)