T5.5K Fossa: A /5 Dirtbike Project

Discussion in 'Airheads' started by Stagehand, Feb 15, 2009.

  1. Stagehand

    Stagehand Imperfectionist

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    Haha- I just wrote and deleted about 10 openings to this... Cant quite get any one that expresses my feeling properly, but HOLY CRAP I just took delivery of a little bit of a dream:

    [​IMG]


    I have held off on doing any more than mentioning it in very passing circumstances, because in my line of work, nothing is a guarantee until you are on the bus on the way to the gig, and even then you never know, but now the thing is in my garage, and its MINE MINE MINE ALL MINE AHHHAAHHHHHHAHAHH

    ok.

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    I have not had my hands on it before this. Have not built one iota of it with my own hands. Merely contributed some theoretical design elements.

    [​IMG]


    We are looking at a 1972 R60/5 with Honda CR250 41mm forks.


    [​IMG]


    I can not WAIT to ride it around.

    It needs a battery,some electrics, footpegs, cut and weld the foot control levers, and fenders. I have a tank, but it needs paint. Well, it doesnt REALLY need paint, but it does need petcocks, and paint would be nice.

    Actually I've got a ton of stuff to do to it before I start racing it in some local stuff, and I cant wait to hear what you guys have to say.

    [​IMG]

    [​IMG]


    Lots of details, but I think it weighs about 300lbs.


    [​IMG]


    HOLY CRAP we got some work to do, but OH MAN Its going to be worth it.


    LETS RIDE:deal
    #1
  2. Bloodweiser

    Bloodweiser honestly

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    your life just keeps making me more jealous every day :deal

    ....I'll be keeping an eye on this one ! :wink:
    #2
  3. datchew

    datchew Don't buy from Brad

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    you need to have another kid so you're slowed down to my pace. :deal

    +1 on the jealousy thing.

    And you'll need some air filters. :D And we need wheelie pics!
    #3
  4. datchew

    datchew Don't buy from Brad

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    email sent. Thought it appears there were mods done to the brake part.
    #4
  5. grimmboy

    grimmboy Chris Grimm

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    I've already added my insider 2 cents other than it needs high-pipes as well. Now get to work I'm bored sitting here mending my ankle.

    Love ya, Grimmy
    #5
  6. TEXASYETI

    TEXASYETI Call me "thread killer!"

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    :eek1

    I am impressed! This should be a fun one for sure!

    More pics of everything. Keep us updated, I am interested to see how this one turns out.
    #6
  7. Stagehand

    Stagehand Imperfectionist

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    Cool- sweet, thanks guys..

    Oh Hey- maybe perhaps a mad could add "/5 Dirtbike" to the title, to make it so possibly you know what the hell this is about? :evil :D

    Here's the link to the smugmug site:
    http://jasona.smugmug.com/gallery/7261322_e8gkG#P-1-12

    and here's more photos for the less inspired:
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    #7
  8. anonny

    anonny What could go wrong?

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    Now I understand the dead loss battery post better. :D
    #8
  9. SUVslayer

    SUVslayer Long timer

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    Looks like fun! Can't wait for the first ride report.
    Looks like you need some duct tape for that seat.
    #9
  10. Cordless

    Cordless Two Wheel Addict

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    What kind of suspension travel do you expect to have when it's in racing trim?

    What mods make that driveline angle possible?

    Is that a cruise control (throttle lock) bolt on the throttle assembly? (That should come in really handy while waving to the crowds on your victory laps.)

    We await a competition comparison between this /5 dirtbike and the African Desert F800GS.

    (Now I understand the porno shot in the Friday photo thread, finally.)
    #10
  11. notarex

    notarex Can U taste the waste?

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    Oh man that thing is crying for a Baja Designs 8" Racelight :tb
    #11
  12. Stagehand

    Stagehand Imperfectionist

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    OK, its at the welder friend of mine's getting some footeg action. Meanwhile lets talk about stuff I'm not ready to do yet.

    http://www.advrider.com/forums/showthread.php?t=433393

    Frank's right, I need to meter it to see what the ignition draw really is, then size a battery to handle my needs. Handle My Needs. I have needs. :deal


    SO whats it gonna take to fit a magneto to this thing? Has anybody ever bothered to do such a thing? I'm not too familiar with magneto's, (or, you may have already noticed, ANYTHING I do here) but am attempting to educate myself.


    OK, also- I am hoping to arrange my brake lever to do somehting like this:

    [​IMG]


    Here's an HPN solution:
    http://www.hpn.de/bilder/high_resolution/sixdays_gs_r1.jpg

    Current unit is a hacked off aluminum stock. Was going to run it underneath, but now having looked a little closer I want it over the footpeg.

    Also, you can see how HPN uses an armature for the shift lever, while I am planning on trying a foreshortened shift lever. Just a little stubby.

    [​IMG]


    In that Sixdays shot, above, it looks like they've made the bash plate into the oil pan! :eek1 clearance?

    Cool airbox thought process, and I see the crankcasevent.

    Fuel Lines are RIGHT NEXT to exhaust.


    This guy has his swingarm gussets going aft, an interesting feature.

    http://www.vintagejerry.com/JaysBMWdirtbike.htm

    that exhaust is making me cry :cry



    Brake Lever: ala HPN:
    http://www.hpn.de/bilder/high_resolution/baja85-2.jpg


    http://www.hpn.de/bilder/high_resolution/paris-dakar86.jpg


    And also from looking at these, my footpeg placement looks like it generally lines up with where these are landing, just forward of where the frame goes vertical. It seems like I'm aiming to have my heels tap the pivot covers.

    Next installment: exhausts. Maybe. :D I've got an R80ST stock muffler that would be nice and quiet (for my woods) but weighs a metric ton. I want to think of something that is relatively quiet and not going to get destroyed every time I hit a rock.

    [​IMG]

    [​IMG]

    There doesnt seem to be an obvious nice easy cheap good solution waiting to beat me over the head with its simplicity. Dammit.

    [​IMG]

    Its going to be interesting getting up and around the shocks. Its gonna seem like its sticking way out there... I'
    #12
  13. Stagehand

    Stagehand Imperfectionist

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    I dunno how much travel, exactly. I would be lying if I took a guess, but when I sat on it it was really plush. I will try to figure that out later.
    I'm thinking I have to remove the shock springs so I can move the shock/rear wheel by hand to get an accurate measurement. What I'll most likely do is eyeball a tape measure while sitting on it and not. :freaky

    There is a small notch in the rear frame brace just above the swingarm to let it go down just a little further. It shouldnt see any time at max lower extention, because that would presume I am getting the back tire off the ground. :rofl Most of the tie it will have at least my weight or some fraction thereof to keep it in line. Shocks should prevent it from going outside the shaft's limits. THe notch was plated with flat stock, so there is no gap, and its whole again.

    [​IMG]


    It is a throttle lock, i think, because its from a modified /5 perch. :D victory lap- you make me laugh :lol3


    I'll give you a sneak preview early comparison:

    I would not kick the 800 out of my garage, but this one makes me salivate, and make little love noises
    unconsciously.



    I need to make sure the kickstart can clear the footpeg.

    Nachtflug pointed out there is a guy selling a sweet R90 dirtbike over in the Flea Market. It looks like a really cool bike.
    #13
  14. Caddy82rats

    Caddy82rats Long timer

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    So nice project !
    keep us posted
    Instead of magneto, why note using a moped unit (electronic and no need of accumulator), or a huskvarna enduro unit ? , you maybe have to deal with thhe spark timing, but some of them had a timing curve
    #14
  15. Stagehand

    Stagehand Imperfectionist

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    Thanks for that info... can you tell me more, before I just start googling toute fou?

    I found out the rear diff is a 37/11. Could be lower, but its on the low side so its not bad.
    #15
  16. bgoodsoil

    bgoodsoil Dare to be Stupid

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    how have I missed this thread?!

    I like your solution(or whoever did it) to the fork stops. I JB welded some little blocks on the frame for the DR forks I put on. Still need to post pics in the 'Unholy Union' thread.

    Do you know if any cutting/relengthening was done on those forks or were they just bolted up? From what I can find the CR250 had inverted forks all the way back to '89 making those some pretty old forks. Wheel travel would have been around 12"

    http://www.cyclechaos.com/wiki/Honda_CR250R

    I'm hoping to flip my brake lever so the rod runs above the swingarm next week(if I can get through a midterm and another freakin Spanish essay). Since you've got the brakes actuated by a rod like the G/S the same mod should work for you. I'll post up some good pics on how to do it next week, i hope. I'm only saying that because it may affect whatever you do with the brake pedal and this bike is just crying out for cool-offroady things like that.
    #16
  17. bgoodsoil

    bgoodsoil Dare to be Stupid

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    oh yeah, and that plate that holds in your axle uses 4 studs set in to an aluminum block. You CAN pull those studs if you overtorque them. i really recommend getting some nylox (probably 6mm) nuts so that you don't need donkey kong torque to hold them on and you don't have to worry about your front wheel falling off while you ride.

    Screw the headlight--junk you don't need!

    That pic with the tape measure showing ground clearance--is that with the lift taking up the slack in the suspsension, in other words maximum ground clearance? 12" is darn good.

    okay, I give up, what the heck does t5.5k fossa mean? THAT'S why I haven't seen this thread yet!

    Man I'm lookin' forward to this thread. You've got a lot of expectations to fulfill with this sucker!
    #17
  18. Stagehand

    Stagehand Imperfectionist

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    right on!

    builder mentioned the stops should be replaced by steel pins, threaded to drop in to where the bolts are now. I think those are just standard strength bolts... no shear strength to them.

    Forks were just bolted up. They are '96 CR250. so I've been told. I'm getting odd signals, though. They look old. :dunno Pic above shows just a spacer a the bottom to make up a little distance. Otherwise BMW bearings, I think. I think the stem is Honda, and evidently they are similar. I will check that out.

    Googled "honda CR250 41mm Forks" and found out Race Tech might make some nice stuff for them:
    http://dirtrider.automotive.com/927...suspension-vintage-honda-cr-models/index.html


    SHit they may be 43's. they look pretty small. I need to look them again.

    brake pedal-Re: the rod- I have a small shock mount to get around... I have no issue with flipping the bake lever up, but am thinking a cable might be clever.

    fabbing a brake pedal should be good for my soul. I can see the rocking couple- just need to get a piece of metal to understand what I'm thinking.

    Ok- the name is stupid. I'll admit. A fossa is a cat like carnivore from Madagascar related to a mongoose. Badass little woods creature. The T is for the guy who built it and the rest is related to the price. :bluduh :lol

    That 12" is not being lifted at all. Its the bike without rider, fuel, or rear muffler. Otherwise its resting on its laurels, I.e. all other fluids, and gravity. I think it will drop about 2" with me and a tank of juice on it.
    #18
  19. bgoodsoil

    bgoodsoil Dare to be Stupid

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    krikey! How many hours of the Discovery Channel did you have to watch to find that out?!

    seriously, that is the dumbest name for a thread I think I've ever heard. seriously. :lol3

    that's some pretty good ground clearance. In the pics you showed you were up on your heels, just where you'd want it for an offroad bike. Did the rear shocks get changed out too? I mean they don't look original.
    #19
  20. Phreaky Phil

    Phreaky Phil Long timer

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    Hi Stage, Cool project !! I am sure those forks are from a Honda XR250. The vintage is right. They were on the model that ran from early 90s until they stopped making them. I fitted a set to my GasGas Pampera. They are a cartridge fork and there are better cartridge valves avaliable. You can also get an SCR fork brace for them.
    #20