Another dirtbike build "BMWsaBERG"

Discussion in 'Airheads' started by Dmaster, Aug 17, 2013.

  1. Dmaster

    Dmaster Been here awhile

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    After a few years of abusing the R65GS i came to a conclusion: Its a awesome bike but it needs less weight and more suspension travel (and some other details.)

    I have a R100R cafe racer project waiting not to be finished so this will be the base.

    This is the plan:
    - 280mm or more suspension travel front and back.
    - less then 150 kg (with gas, oil battery and starter.)
    - paralever (i don't want the jacking like a non paralever)
    - a wheelbase less then 1500mm (that could (will) be a hard one:wink:)
    - reinforced frame
    - small engine (short stroke R65 maybe with 1000cc cylinders)
    - rear drum brake
    - small main gas tank
    - low center of gravity
    - and a 1000 things to over think before putting them on this list. :evil
    #1
  2. Dmaster

    Dmaster Been here awhile

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    [​IMG]
    Max travel on the rear now is: 285 mm.
    [​IMG]
    [​IMG]
    #2
  3. hardwaregrrl

    hardwaregrrl Can't shoot straight Supporter

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    HOLY SH#@!!!!! That's gonna be a MONSTER.:super:super
    #3
  4. Ras Thurlo

    Ras Thurlo Desert Lion

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    :ear

    esp interested to see how the 1100 paralever vs wheelbase thing works out

    +1
    #4
  5. orangebear

    orangebear Long timer

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    This could be a fun build. Why use a r65 with a 1000 bore. When you could use a r100 motor? It my be a stupid question.
    #5
  6. villageidiot

    villageidiot Long timer Supporter

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    short stroke, big bore, quick rev's
    #6
  7. bromax.ca

    bromax.ca Been here awhile

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    What type of u-joints will you be using? I found the restriction in travel to be the u-joint and/or clearance between u-joint and swingarm.BTW...Love your videos. The Berg plastics and seat looks great on the airhead.
    #7
  8. AntonLargiader

    AntonLargiader Long timer

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    A stock R100GS is over 1500mm wheelbase. According to some calcs I did a few years ago, an 1100 swingarm and 265mm front travel puts you well over 1600mm (like the HP2). You will have to shorten the frame, engine and transmission to get under 1500 with 285mm travel F&R. The Airhead drivetrain is the big limitation: you have front wheel (at full compression) touching engine bolted to transmission adjacent to swingarm pivot plus swingarm length determining where the final drive is. Without surgery, that stack-up is fixed. Measure it yourself; you need to know it.

    Your wish list is admirable. :) But it's roughly the same wish list that I've seen here over and over, and only the very talented fabricators get close to realizing it. Most attempts simply die off and the threads roll off the page into oblivion. Who knows what happens to the cut-up bikes.

    My point isn't to squash your dreams, it's to suggest that you develop meaningful and reasonable goals. Do you really want a heavy bike with 285mm travel front and rear, when every centimeter of travel adds to the wheelbase and height? I'm glad my XR400 has that kind of travel but I'd never use it on my GS. If I rode in the desert things might be different. The KTM SuperEnduro is about 250 and it's probably a great bike to emulate. There's a reason KTM didn't give it 300mm travel.

    Lighter than an R80G/S? Again, you're into major surgery.

    Have you seen this thread? It should be your inspiration:
    http://www.advrider.com/forums/showthread.php?t=30044

    But he still didn't get under 1500mm wheelbase.

    Measure twice, cut once.
    #8
  9. Dmaster

    Dmaster Been here awhile

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    A R100GS should be 1516mm in wheelbase the swing arm = 285mm
    a 1100 swing arm = 355mm a difference of 70mm
    A longer fork will add some wheelbase but I probably use triple clamps with less offset then the stock R100GS triples so i don't think this will add much to worry about.
    In your link (i did see the picture before) he said the frame was shortened 62mm that would be enough to get it back to 1525mm, close enough.
    It would be pretty damn hard to shorten the frame that amount but i'll see what i can get.

    I know its a stupid idea but i think i can build one. I use my R65GS as a dirtbike know and use all the travel in there (255mm front +/-230mm in the back) so my goal is less wight more travel and it could be even more fun than i already got.
    The KTM is still over 180kg and top heavy, thats not what I'm after....
    That would't be to hard, tank is heavy, as also the wheels and exhaust are.
    Lighter than a R80G/S is easy (if you don't mount more parts) going under 150kg will be hard.
    But again, i'll go for it and try to go as far as i can get.

    Have you seen this thread? It should be your inspiration:
    http://www.advrider.com/forums/showthread.php?t=30044

    But he still didn't get under 1500mm wheelbase.

    Measure twice, cut once.[/QUOTE]
    #9
  10. Dmaster

    Dmaster Been here awhile

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    I'll use the stock driveshaft for now. I found the travel i want already.
    Thanx for the compliment on the videos :D i'll keep making them :evil
    #10
  11. Dmaster

    Dmaster Been here awhile

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    The R65 engine has the short stroke, it will make the engine smaller, putting the carbs closer to the engine leaving more space for my legs end feet.
    If i get on a 100GS i immediately notice the difference. Imo its worth the hassle.
    If your doing wide open tracks its no problem, but i like to short stuff all the time thats why i don't want the insane wheelbase.
    #11
  12. ME 109

    ME 109 Long timer

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    Hmmm, sounds like an RS is out of the question then.:D
    #12
  13. Airhead Wrangler

    Airhead Wrangler Long timer Supporter

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    150kg might not be doable without getting seriously savage. Custom frame, drill holes in all your gears, carve extra metal off your final drive crown gear, no starter, etc. Take a look at some of the stuff SWT has done to reduce weight. A LOT of work and he's down to 157 kg with oil.
    #13
  14. Ras Thurlo

    Ras Thurlo Desert Lion

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    what approx weight can you get these bikes down to, before getting medieval?

    what is the basic laundry list of items that give you big savings, before you start getting to diminishing returns?


    #14
  15. Beater

    Beater The Bavarian Butcher

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    WHOA.

    :lurk
    #15
  16. robbiedobbie

    robbiedobbie Robbiemyboy

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    [​IMG]

    My bike is about 160kg with the following mods.

    R65 motor 1000cc cylinders, larger exhaust valves and port. Twin plugged with CDI ignition, no alternator, just a dynamo. R1100GS swing arm with R80 diff. The gearbox is standard other than a lower 1st gear. The exhaust, collector is a single unit and sits behind the bashplate. Forks are from a CR500 has 250mm f+r. Tops out at around 160km/hr. I don't have a photo here but this link will take you to where there is one.

    https://fbcdn-sphotos-a-a.akamaihd.net/hphotos-ak-ash4/382521_10151677560520318_1928995415_n.jpg
    #16
  17. Lornce

    Lornce Lost In Place

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    #17
  18. AntonLargiader

    AntonLargiader Long timer

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    #18
  19. Dmaster

    Dmaster Been here awhile

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    Nice bike!
    Do you have more info on the dynamo? I might be interested if it would make my engine shorter.
    And it would be nice if i could ride it without a battery.
    You still have the "stock" rear wheel (bmw cross spoked) i know thats a heavy one.
    And a steel tank, steel sub frame, luggage rack, etc.
    It could be much lighter :evil, this gives me hope i might made it under 150 kg.
    Max 160km/h, my R65GS (lots of R65LS engine parts) does 164km/h on the GPS with (stock) low gearing.... what went wrong?
    I also might want the 1000cc cylinders on mine, do you got more info?
    Machine the 1000 cilinders down, make a scuisband in your heads and let the fun begin or more difficult things to worry about?

    Not much happened on the project, I'm walking around thinking, what to do first (so much to do :huh)
    Got a fork in on monday need to mount it with a wheel end see how much is there i could shorten the frame.
    #19
  20. DK Dan

    DK Dan Been here awhile

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    Just subscribed to this thread :lurk

    I'd say some of the weight loss came from removing material from the engine case (a better photo of this is seen via the link robbiedobbie inserted).
    #20