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Thread: 1981 gs750 (gs750e) Retro Racer project

  1. #21
    Join Date
    Aug 2012
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    Columbus, Ohio
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    3,595

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    Best to double check individual tire manufacturers reccomendations per tire model for fitment.

    I run a 140 & 150 on DID & Sun 3.50 rims. 140 has every bit as much contact patch and weighs less, as installed on a 3.50. 150/70 fits good, 140 fits best.

    '77 GS750
    920cc, 4-1, GS1100E swinger, 18"rims, Fox Factory Shox, twinpot dual disc, VM29's, Yoshi cams
    '99 Kawasaki KDX220 rugged terrain ripper
    '74 Rickman VR250MX
    PROJECTS:
    '77 Suzuki PE250 Pure Enduro trail beast, ported, Wiseco, TüBliss, Fox Factory Shox/RaceTech
    '76 Rickman CR GS1000-1120cc roadracer, Yoshi cams&4-1, RF900R fork, Works ProRacers
    '79 GS425 489cc, GR650 cams, GS650 fork, twinpot discs, DID rims, GS1100E swinger, Fox Factory Shox
    '77 GS550 650-740cc susp/brake mods

  2. #22
    Join Date
    Oct 2015
    Location
    Aust-Agder Norway
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    304

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    Quote Originally Posted by Chuck78 View Post
    Best to double check individual tire manufacturers reccomendations per tire model for fitment.

    I run a 140 & 150 on DID & Sun 3.50 rims. 140 has every bit as much contact patch and weighs less, as installed on a 3.50. 150/70 fits good, 140 fits best.
    Will do

  3. #23
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    Aug 2012
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    Columbus, Ohio
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    You also need to take into consideration the ride height changes due to tire size changes. Overall, about 1" total combined steepening of rake over stock oem sizes is good for cornering. Going with a 110/80-18 or 100/90-18 over the stock 3.25(?)x19 will help quicken steering by dropping the front slightly. Then a 150/70-18 or 140/80-18 will raise the rear up a bit as well. Assuming you are using GS triple clamps still. I prefer a 140/70-18 and 110/80-18 and taller rear shocks than stock to get a good quick feel to the steering.

    If swapping modern forks, try to stick with 41mm RSU tubes so you can run GS1100GK triples or Honda PC800 triples with the steering stops modified to work with a GS frame.

    CBR600F4 forks are great in VMAX 1200 43mm (93 or 94+ models 43mm tubes) triples but may require slight milling the backsides of the calipers for more spoke to caliper clearance.

    GS1000 dual disc fork legs are the easiest swap on most big gs's, Sonic Springs and Racetech Gold Valves or Ricor Intiminators and you're home free with the tire diameter and shock length changes. Much better steering, 37mm stiffer fork legs as well. I have pushed my 35mm 650 forks on a 750 to the limits as well. I noticed some flex at high speeds and aggressive cornering, but the bike handled wonderfully with fork spring and valving g upgrades, Tarozzi fork brace, piggyback shocks sprung and valved for the bike. Of course going to RF900R (shorter version of Bandit forks) cartridge forks may have me seeing what I didn't know I was missing out on, but the 35's modified did the job pretty well.

    '77 GS750
    920cc, 4-1, GS1100E swinger, 18"rims, Fox Factory Shox, twinpot dual disc, VM29's, Yoshi cams
    '99 Kawasaki KDX220 rugged terrain ripper
    '74 Rickman VR250MX
    PROJECTS:
    '77 Suzuki PE250 Pure Enduro trail beast, ported, Wiseco, TüBliss, Fox Factory Shox/RaceTech
    '76 Rickman CR GS1000-1120cc roadracer, Yoshi cams&4-1, RF900R fork, Works ProRacers
    '79 GS425 489cc, GR650 cams, GS650 fork, twinpot discs, DID rims, GS1100E swinger, Fox Factory Shox
    '77 GS550 650-740cc susp/brake mods

  4. #24
    Join Date
    Aug 2012
    Location
    Columbus, Ohio
    Posts
    3,595

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    Sorry, failed to clear that up. Taller diameter rear tire and/or taller rear shocks combined with shorter front tire (18" swap) to give you a combined 5/8" to 1" change in ride pitch, adding together the extra height in the rear with the difference in lower height up front, for 1" total change, will give you GREAT quick nimble agile handling on these very stable GS's

    '77 GS750
    920cc, 4-1, GS1100E swinger, 18"rims, Fox Factory Shox, twinpot dual disc, VM29's, Yoshi cams
    '99 Kawasaki KDX220 rugged terrain ripper
    '74 Rickman VR250MX
    PROJECTS:
    '77 Suzuki PE250 Pure Enduro trail beast, ported, Wiseco, TüBliss, Fox Factory Shox/RaceTech
    '76 Rickman CR GS1000-1120cc roadracer, Yoshi cams&4-1, RF900R fork, Works ProRacers
    '79 GS425 489cc, GR650 cams, GS650 fork, twinpot discs, DID rims, GS1100E swinger, Fox Factory Shox
    '77 GS550 650-740cc susp/brake mods

  5. #25
    Join Date
    Oct 2015
    Location
    Aust-Agder Norway
    Posts
    304

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    Thanks for all the info

    Today I made a prototype for the top clamp:







    I have couple of questions though.. It was quite hard to get the measurements right. Does anyone know the spacing between the big (35mm) holes and how much offset the small hole is from the two others? I also noticed that the center hole is drilled at an angle, anyone know what angle this is? The long hole is for fitting a Motogadget Motoscope Mini:



    Here's also a video of the milling process:



  6. #26
    Join Date
    Oct 2015
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    Aust-Agder Norway
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    Today I had som extra time and sat down to make at 1:1 scale blueprint of the seat.


    First I checked the proportions and measurements in Gimp:





    When I had all the coordinates I drew the seat up in three planes:





    Tomorrow I'll try to make the framework somehow. The plan was to cut it out in MDF-wood and glue/screw the pieces together, but I see people also weld together a wireframe first, then weld the sheet metal to the frame. I'll spend some time with Google and see what I come up with.

  7. #27
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    Oct 2015
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    Aust-Agder Norway
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    I've started on the buck for the metalshaping of the seat, but I needed to visualize it on the computer before finishing it.






  8. #28
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    Oct 2015
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    Aust-Agder Norway
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    A couple of images from the building process. This shows how I'm making the buck.





    Last edited by LarsKroghStea; 01-29-2018 at 10:53 AM.

  9. #29
    Join Date
    Oct 2006
    Location
    So Cal
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    HOLY CRAP!!! You have too much free time!!! LOL!!!
    Ray.
    85GS1150E 83GS1100ESD 83GS1100SD 83GS1100ED 82GS1000SZ 96GSXR1500Dragbike 96GSXR1400Dragbike 90GSXR1166Dragbike 04SDG110PITBIKE + 8 Quads! "Life is tough! It's even tougher if you're stupid!" John Wayne

  10. #30
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    Oct 2015
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    Aust-Agder Norway
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    Quote Originally Posted by rapidray View Post
    HOLY CRAP!!! You have too much free time!!! LOL!!!
    Ray.
    Haha Not really, just needed something to do on the computer while the wife was watching Sons of Anarchy The bikebuilding is as important as the riding and I like learning new stuff and new ways to do things

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