BMW frame strengthening

Discussion in 'Airheads' started by Paul_Rochdale, Sep 20, 2012.

  1. chasbmw

    chasbmw Long timer

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    Back then I went RTW on standard airhead road bikes, two up with camping gear (pre GS days). Quite a lot of the roads out side of Europe and north America were pretty rough, but a set of standard Craven panniers worked fine with only a little bit of remedial welding required in Ecquador. Australia included a lot of dirt roads, some rough.

    Spend your money on the toughest suspension you can find and does not mean Ohlins. Plus decent panniers. Modern tents are very lightweight and I still enjoy sleeping under canvas, even if I eat out.
    #21
  2. pommie john

    pommie john Long timer

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    That looks a very nice and sensible mod. Very neat.


    Paul, you know you're quite close to Jim Cray who is a bit of a BMW guru. he's in Faversham.

    Next time you're in the Little Gem, have a pint for me :1drink
    #22
  3. robtg

    robtg Been here awhile

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    You have got to be kidding. :huh
    #23
  4. Jim Day

    Jim Day full manic mechanic

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    I KID YOU NOT!!! ha ha ha

    There's a bunch of German guys doing these frame mods, I'll see if I can scrounge up some pics, but it's been a while since I looked at them. The drag for me is I do not speak German so it's always hard to find them online.

    .......time passes :D

    So I couldn't find the website I wanted but I did find some pics on a old hard drive of mine, but none with the longer cross brace.

    These first few are from one guy who I believe is German, He does incredible frame mods and custom builds. He used to have a website, but I couldn't find it any more.

    Here's some pics of one of his:[​IMG]

    [​IMG]
    You can see the plate they put in front of the swingarm to minimize stress and prevent cracking.


    Here's some other bikes with that same modification. It's pretty standard I've seen it all over the place.
    [​IMG]

    [​IMG]

    PersonallyI find that mod kind of ugly but that's the way they do it and it does make sense. So that's the one mod I'll look around some more and see if I can find some pics of the frame cross braces.
    #24
  5. gsd4me

    gsd4me 90% bluff

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    [​IMG]


    [​IMG]
    #25
  6. Jim Day

    Jim Day full manic mechanic

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    Nice Bike!!! I've seen that cross brace as well. It makes a lot of sense especially on a road bike where most of the pressure on the frame comes from the drivetrain. Personally if I was going to go with that brace I'd install the little swingarm plate I pictured above but instead of making it pointed I'd make the top wider, square, with a hole for mounting that brace. That way you get the benefits of the plate and a strong mounting point for the cross brace. I've also seen a top cross brace that supports the upper sub-frame mounting area. It would not be necessary on a road bike but I suppose that one does make some sense for off road use since that mounting point is being worked by the more intense demands on the rear suspension.
    #26
  7. Crisis management

    Crisis management Latte riders FTW!

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    You mind telling me a bit more about this bike, turbo & injectors??
    #27
  8. Paul_Rochdale

    Paul_Rochdale Been here awhile

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    I would like to but it's been closed for two years with no sign of anyone wanting to buy the place. I know Jim Cray pretty well as eighteen years ago he rebuilt the engine of my R100/7. He is also going to check over my R100GS-PD engine too. I finally decided on making fillets along the lines of HPN and Dogbytes mods. This will strengthen the frame as I wanted but won't go the diagonal brace route as it's not necessary for the sort of riding I've planned. I shall re-use the existing Hagon monoshock - they will rebuild them for about £90 - as it still looks as if there's life left in it. Thanks for all of the tips and, as was said, I shall be doing it my way. I shall be speaking to a local custom bike builders about welding/bronze welding the fillets I've made.
    #28
  9. gsd4me

    gsd4me 90% bluff

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    Owned and built by South East Queensland BMW repairer Ray Peake. He`s had it for over 25 years and has over 290,000Km on it, very reliable.

    It doesn't get used much these days as he also has a much improved what was originally an R80 GS/PD and more recently an R65 mono w/- 1070cc kit and FI .

    I think he pretty much built the FI injection himself, along with everything else on the bike; 18 inch front wheel, wider rear wheel, rear disc, etc, etc. The longer you look , the more modifications you see.

    He's done a few good specials over the years, as well as bringing sad, (mostly airhead GS`s) back to life with the upgrades they need to be more reliable.

    http://www.advrider.com/forums/showthread.php?t=768885&highlight=r100gs+build+australia
    #29
  10. gsd4me

    gsd4me 90% bluff

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    All very good advice. Back "in the day" it was well known in Oz that the /5, /6, and /7 subframes were weak and a Craven rack helped beef things up.

    Hyperpro is the rear suspension I would choose over anything, these days.
    #30
  11. ms-oz

    ms-oz Mike

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    I own a R80 G/S HPN 1986 and ride by far not hard enough to make use of all the benefits the frame bracing is doing.
    During a holiday last year I went to see the HPN workshop and had a good look around what they have built in the past and what they still build, and have had long discussions and picking their brains about the frame reinforcement.
    They have a full collection of Paris Dakar bikes from 1981 to the oil heads.
    The strengthening they do to the GS is to make the bike better putting up with the impact
    coming from working the suspension (jumping and corrugated roads).
    HPN did actually develop and engineer the frame for the BMW Krauser MKM 1000.and later sold it to Krauser who then started manufacturing a small series. The diagonal bracing from steering head to the swing arm pivot point is designed to minimise the twisting of the frame (high speed direction changing) with putting that in you are improving your frame towards the Krauser style of bike. The collection at HPN includes also at least one of these 'MKM' that is still road registered and gets raced.
    With strengthening in the HPN GS way, putting the half moon around the pivot point, and several bracings around the steering head reinforcing the shock mount and foot peg mounts you develop your frame towards a desert racer or around the world mule. If you look at the variety of the sub frames some of them are designed for a light weight rally bike while others are made to mount luggage carrier to it.
    http://www.SWT-SPORTS.de is offering a kit of strengthening plates that a guy here in Perth has used to build a HPN relica.The white bike on:http://www.advrider.com/forums/showthread.php?t=787760 the bike with the red frame is a replica of a replica, he copied the SWT parts and my bike design.
    #31
  12. chasbmw

    chasbmw Long timer

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    I would really like to build a Krauser framed bike, fit a tweaked engine, give it an 90/S riding position........isn't their some wear in holland that builds Krauser frames?
    #32
  13. Alfons

    Alfons Been here awhile

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    #33
  14. ms-oz

    ms-oz Mike

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    I like these frames
    [​IMG]
    [​IMG]
    [​IMG]
    #34
  15. Rucksta

    Rucksta SS Blowhard

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    Why?

    Long wheelbase with a short swing arm - thing will be twitchy at the point it breaks traction.
    Little if any increase in rigidity to adress "rubber cow" syndrome and a larger unsupported triangle mounting the rear shocks is going to further amplify rubber cow effects.
    Looks to me to be an exrecise in styling rather than engineering a rigid frame with improved handling.

    Does it have a race history that says I've missed the point entirtely?
    #35
  16. Prutser

    Prutser Long timer

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    In the Netherlands guys with those frames win a lot of classic races. So they must be doing something right.

    [​IMG]
    #36
  17. Rucksta

    Rucksta SS Blowhard

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    Thanks for that.
    A beemer looks good at the front of the pack.

    # 44 looks like an H2 Kawasaki yet it appears to have drum brakes.
    Is it a waterbus or are drum brake conversions required for vintage racing in the Netherlands?

    As an owner and rider of multiple triples I know that to make any BMW handle as well as the Kawasaki or Suzuki triples you have to first let the air out of the tyres.
    #37
  18. pommie john

    pommie john Long timer

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    In Europe a yellow number plate means 500cc, a 750 would have white plates. The blue plate on #34 in the backgound means it's a 350.

    Maybe #44 is a 400 Kwacker? Did they have drum brakes?
    #38
  19. DoktorT

    DoktorT BigBrowedNeandereer

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    That sounds very much like an RS/RT, or really any R100 airhead set up for touring as you like it. Purpose designed for long range road touring on good roads. If you are on 3rd world roads, the GS might be better.
    #39
  20. DoktorT

    DoktorT BigBrowedNeandereer

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    Must say that is a very elegant triagulation design. Kudus to whomever made that.
    #40