s90 sporty front end from dirt parts
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s90 sporty front end from dirt parts

This is a discussion on s90 sporty front end from dirt parts within the Technical forums, part of the Caferacer.net Forums category; I have a sloooowly progressing s90 project that I would like to make into a fun 5 mile commuter. I definitely want to upgrade the ...

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  1. #1
    Senior Member kerosene's Avatar
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    s90 sporty front end from dirt parts

    I have a sloooowly progressing s90 project that I would like to make into a fun 5 mile commuter.

    I definitely want to upgrade the forks as the current are quite shot and generally crappy - doubt they were very good as new either. Some time ago I got decent pair of sl 100 forks (31mm vs. 27mm stock pogo sticks)

    so my current plane is to use those forks shortened with sl100 or sl125 triples, yz85/kx85/cr85 17" front wheel and disc brake.

    Dirt bike wheels are quite cheap and plenty available - generally the issue is that the hubs are very wide and need very wide fork spread - I haven't been able to find how far apart the forks are on 80cc bikes but would hope they are way narrower than on bigger ones.

    Another issue is that I would need bracket for the disc break welded on the fork down tube. I have access to good quality TIG machine and am practicing that stuff now. Is welding a bracket a dumb idea all together? Remember this is < 10 hp bike.

    If plan described above has some major holes please let me know.


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  2. #2
    Senior Member crazypj's Avatar
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    welded on stops has been done many times.
    You probably want to pay professional weldor though as distortion of slider is quite common. (weldor is person, welder is machine you weld with)
    Easier to get complete front end of later CB125, if you don't mind messing with cable disc or Suzuki GP100/125 as they came with hydraulic brake. I think Kawasaki or Yamaha may have something but don't remember trying to fit from those?
    S90 only has 7~8bhp, I spent a lot of time 'playing' with them.
    A CB175 piston fits and makes it (if I remember right) 112cc
    With some porting, larger carb and 'decent' exhaust it will hit 90mph (70~75mph in third) but crank doesn't last very long because of the rpm and clutch has to be slipped to 10~15mph because of high gearing./

    PJ
    I dabble in rocket science, when I\'m not picking my nose
    The other night I gave my girlfriend an orgasm, but, she spat it back at me

    'you can take my word for it or argue until you find out I'm right'

  3. #3
    Senior Member kerosene's Avatar
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    Cool thanks,
    I have actually a sl70 engine in it right now (lower 4th gear - not sure if other ratios are tighter too). And I have a ported head that I need to get new guides in waiting for future work. The little riding I did with the bike the terrible suspension was the biggest issue - I am relatively big guy - 6'4" 200lbs and live in Los Angeles where we have 3rd world country style pavement on 40mph streets. I would be still bouncing up and down 50 yards after the bump.

    I like the idea of the sl100 forks as they are not that much too long and feel like well damping "real" forks. And they are way easier to come by than cb125 forks.

    I don't mind the "custom" work of spacers an brackets. I take a machine shop class (more like do your own projects style - ongoing) so I have access to good lathes and milling machines etc. There are couple of really experienced weldors amongst the regulars and I think one of them will have the skillset to do a good job on the stop.

    Also I don't need 90mph - just decent acceleration to 55 or so.
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  5. #4
    Senior Member crazypj's Avatar
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    It probably has the original fork oil?
    Rear dampers are (Hmm, don't have a word for total shite/dangerous/crap, etc)
    just about anything will b an improvement over stock.
    Main problem is finding something long enough without too much travel and still have clearance on chain side.
    You could probably pick up a Chinese knock off motor reasonably cheap and have a 145cc motor?

    PJ
    I dabble in rocket science, when I\'m not picking my nose
    The other night I gave my girlfriend an orgasm, but, she spat it back at me

    'you can take my word for it or argue until you find out I'm right'

  6. #5
    Senior Member raven's Avatar
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    yeah im pretty sure you can get a cheap 4 speed 145cc. I got a 110 under my workbench right now waiting for a suitable frame...S90s are unobtainium here. have you considered one of the xr70/xr50 clone hubs setup for a disc brake laced to a 17" rim?

    This makes me wonder if a 17" rim would fit under a set of the cheap extended pitbike forks on something like an S90. my gut feeling is no, the tire will be too close to the neck and bottom triple clamp.
    Bike:
    Buell X1
    Honda S90 (box of parts)
    Honda CB750C (runs)
    The Others (mostly rolling wounded)

    My collar may be a little frayed, and maybe I need a shoeshine. But nobody\'s got a mortgage on my soul. I own it. Free and clear. -Phil Lovecraft

  7. #6
    Senior Member Swagger's Avatar
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    from an email I get from the kat who built it:
    The front and rear
    rims are from dirt bikes. The front forks, rear shock, front and rear
    brakes, and motor are all pitbike stuff off ebay. The motor is a GPX
    from pitsterpro.com.


    I've got a couple S90s and a lifan 150cc, I think there's a yz80 dead out back for hubs and brakes, the pitbike parts are easy to get. The forks I've been looking at locally are 40mm USD, externally adjustable comp/rebound damping etc etc and come complete with really clean milled aluminum triples that will take the S90 stem easily. They're $200.
    Great spirits have always found violent opposition from mediocrities. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices, but honestly and courageously uses his intelligence and fulfills the duty to express the results of his thought in clear form.
    ~Albert Einstein

  8. #7
    Senior Member raven's Avatar
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    I wonder if you could adapt a single downdraft from like a FZR400 (didnt those have downdrafts???) to that engine. That would look really cool. That bike is pretty much exactly what i want to do with my chinese engine1
    Bike:
    Buell X1
    Honda S90 (box of parts)
    Honda CB750C (runs)
    The Others (mostly rolling wounded)

    My collar may be a little frayed, and maybe I need a shoeshine. But nobody\'s got a mortgage on my soul. I own it. Free and clear. -Phil Lovecraft

  9. #8
    Senior Member Swagger's Avatar
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    I don't see why you couldn't, kinda been thinking about a downdraft carb for mine too....
    Great spirits have always found violent opposition from mediocrities. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices, but honestly and courageously uses his intelligence and fulfills the duty to express the results of his thought in clear form.
    ~Albert Einstein

  10. #9
    Senior Member raven's Avatar
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    I might go to the "local" (100 miles one way) bikeyard tomorrow and see if I can myself an s90 to play with
    Bike:
    Buell X1
    Honda S90 (box of parts)
    Honda CB750C (runs)
    The Others (mostly rolling wounded)

    My collar may be a little frayed, and maybe I need a shoeshine. But nobody\'s got a mortgage on my soul. I own it. Free and clear. -Phil Lovecraft

  11. #10
    Senior Member raven's Avatar
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    So wait....are those pitbike forks on that bike????
    Bike:
    Buell X1
    Honda S90 (box of parts)
    Honda CB750C (runs)
    The Others (mostly rolling wounded)

    My collar may be a little frayed, and maybe I need a shoeshine. But nobody\'s got a mortgage on my soul. I own it. Free and clear. -Phil Lovecraft

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