NORRA 1000 R75/6 Race Bike

Discussion in 'Airheads' started by Linex08, May 7, 2018.

  1. Linex08

    Linex08 n00b

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    9
    Hello Adventure riders,

    My name is Matt, Here is a little info on me:
    I'm a 28 y/o MBA candidate at the University of North Texas in Denton, Texas.
    I recently entered my 1976 BMW R75/6 in the 2019 NORRA 1000 vintage class.
    I've been published in the June 2016 issue of Motorcycle Classics for my '77 Ducati 900SS, featured on a few Instagram post for my old BMW R90 and R80. I've ridden long distance on/offroad trips in America and Peru. I fairly competent in my mechanical ability regarding airheads, but have never done anything like this before.

    Currently the R75 is torn down, engine has a new rear main seal, bead blasted, freshened rings and is awaiting new valve seats. Its running the stock bore and stroke for simplicity sake. The frame was intended to be a street scrambler, but I decided to get crazy and enter this race.

    My main questions are, and I've seen them mentioned on this site via random searches, what is the best way to extend the swing arm to allow me to run 17" rear shocks and stock rear wheel. I'm basing my thoughts off the old HPN bikes. Utilizing a used KTM 690/950/990 front end with 21" wheel.

    Best places to gusset the frame and neck tube?
    Best way to keep silt and dust out of the engine and breathing tubes?

    Should I just keep it fairly stock and run it as far as it goes? (bottom pic)

    I've just started this build and am quite poor, currently moving, and jumping over to Europe for a month (why I'm so poor, irony) so it will be a slow build.

    But if anyone has tips or advice from failed or successful modifications, please let me know.

    Attached Files:

    #1
  2. infinityedge

    infinityedge Been here awhile

    Joined:
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    WP 4860 conversion thread:

    http://advrider.com/index.php?threads/an-unholy-union-iii-wp-4860-usd-forks-on-an-airhead.735725/

    Though if you haven't bought the WPs yeat, you might want to think about DRZ (or late 90s RM) forks

    http://advrider.com/index.php?threads/an-unholy-union-v-drz-forks-on-an-airhead.989832/

    The only way to get more rear travel is with a swingarm extension (17"? typo?)

    http://advrider.com/index.php?threads/an-unholy-union-swing-arm-modifications.1258116/

    Frame bracing: can't find the link to the HPN style plate diagrams, but there is always Jim Day to make you drool:

    http://advrider.com/index.php?threads/brace-yourself-part-2-r65-frame.1226342/

    Dust will suck. Best to stick with the stock paper filter and have an extra ready if needed.
    #2
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  3. One Less Harley

    One Less Harley OH.THAT'S GONNA HURT

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  4. Jim K in PA

    Jim K in PA Long timer

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    Welcome to the asylum, Linex, and a hell of a first post! :thumb
    #4
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  5. bajaburro

    bajaburro Ancient Adventurer

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    It's really not a race so ride at your own pace and have fun.
    #5
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  6. KLEINE

    KLEINE oo

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    #6
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  7. ME 109

    ME 109 Long timer Supporter

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    I think only flying airheads need bracing for landings. Lot of work for nothing otherwise.
    #7
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  8. Airhead Wrangler

    Airhead Wrangler Long timer

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    I'd disagree. The handling and suspension improvements of a braced frame are well worth it even if you don't need the added strength.
    #8
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  9. KLEINE

    KLEINE oo

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    Same here I am verry happy with my bracing, I used SWT sports plates. I was lucky and had a old colleague who could Tig it on the frame.

    But yes if you do not have the means. Before I started to modify the bike I drove it stock for a season.

    It was already great fun! You can take it (almost) anywhere just as it is. People have done this with airheads before, probably trough more gnarlyer terrain than most of us travel.
    #9
  10. KLEINE

    KLEINE oo

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    [​IMG] Elspeth Beard on a BMW R 60/6 flat-twin
    #10
  11. Wirespokes

    Wirespokes Beemerholics Anonymous

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    If I were doing it, I'd copy the ISDT bikes from around 1970. I'd keep the wheelbase short as possible and if more rear travel/ride height was needed, perhaps tilt the front of the engine up a little like some race bikes. The longer and bigger the front forks the more stress on the frame, plus the longer wheelbase (due to lengthening the swingarm as well) makes it more difficult riding in the woods. The long wheelbase, tall bikes are best for fast desert racing. Keeping it light and short, a less beefy suspension is needed.
    #11
  12. cavebiker

    cavebiker Old School Adventurer

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    Sweeet! You will have the time of your life. I believe 1976 puts you in the Super Vintage class, and if you finish in that class you will have a good chance at the podium. All I suggest is posting this in the Racing forum, you will for sure get all the advice you can handle for racing your BMW in the Baja desert. -->Also maybe look at my NORRA 1000 Racing thread, there is a lot of great info for a inmate doing NORRA for the first time <--

    Whats the latest in the build? How are you training for the 1,300+ mile race? Bring it ON!:happay
    #12
  13. Linex08

    Linex08 n00b

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    Update: I’ve gone with a Drz400SM front fork with 21” front wheel off a Drz400S. I am lengthening the rear swing arm possibly 50mm or more. I’m having two swing arms and drive shafts made incase of failure on the course. I’m also teaching myself to tig weld and fabricate a custom air intake and exhaust to help fight against the sand and silt. I’m basing my design off of the Biltwell sportster that recently finished the race. I’ll post more photos when I can.
    #13
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  14. Linex08

    Linex08 n00b

    Joined:
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    Made a little progress with the bike.

    Front Forks: 2006 DRZ400SM Adjustable pre-load and dampening.
    Rear Sub-frame: Down and Out Cafe, made in England. I was originally going to do a fun little scrambler build before knowing about the Norra. Whether this sub-frame will remain is undetermined. The welds are very nice and seems to be strong.


    upload_2019-1-11_19-20-59.png


    R75/6 engine block has been broken down and soda blasted, new timing chain installed. I'm tempted to go with a larger displacement head/piston kit (Sievenrock or Motoren-Isreal)?
    upload_2019-1-11_19-26-18.png
    upload_2019-1-11_19-26-27.png

    As far as the front forks go, the suzuki trees were basically plug-and-play. Needing only a easy bearing swap, (BMW Bearing: 52/28/16, DRZ Bearing: 55/30/16, Bearing you want to order is 52/30/16).

    In this photo below, is the space for a small aluminum spacer I'm having a friend machine to go above the top bearing and top triple clamp. upload_2019-1-11_19-30-14.png

    Here are some other photos of the bike and sub-frame.
    #14
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  15. Linex08

    Linex08 n00b

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    Photos of the sub-frame. I do not know at this point if I will be using it. I would like to keep the "scramber" vibe but have a full-on race bike. Currently looking at paralever/monolever swaps. If anyone can point me to someone with a step-by-step process, that still has live links and photos, (preferably written in crayon too so I can easily follow along) I would really appreciate it. Thanks -Matt
    upload_2019-1-11_19-32-1.png
    upload_2019-1-11_19-32-11.png
    #15
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  16. Linex08

    Linex08 n00b

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    Thank you, I went with the DRZ400SM forks and front wheel!
    #16
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  17. Jim K in PA

    Jim K in PA Long timer

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    I dig the work table. Split 2x8s?

    If the block has 99mm spigot holes, save your $$ and get a set of good used R100 Nikasil barrels and pistons and some later heads. It will make plenty enough power for a Rally bike.
    #17
  18. Linex08

    Linex08 n00b

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    Thanks, my roommate and I built it. it took me two days of planning to get it all leveled out. On top of each board being glued together, t also has three 24" all-thread rods spread out through it to make sure nothing comes apart.

    As far as the engine goes, I also thought about keeping the factory R75 heads on there just for the sake of reducing stress/abuse on the drive-train. It's going to take a beating out there.
    To quote the offroad world, "it's better to be under-engined and over-axled than vice versa."
    #18
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  19. Jim K in PA

    Jim K in PA Long timer

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    Yep, the less stress the better.
    #19
    Linex08 likes this.
  20. Plaka

    Plaka Brevis illi vita est

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    I ran a R90 top end on a 75/5 block and it worked fine, although the /6 block is stronger. The rear wheel spokes and alternator rotor were weak spots with the stock /5 gearing. Single row timing chain and lightened flywheel will make the engine more tractable.
    #20
    Linex08 likes this.