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1977 GT500 - to do list

This is a discussion on 1977 GT500 - to do list within the General forums, part of the Caferacer.net Forums category; Yep, I was going to say fit some air valves / caps in the forks. Like 8 to 12 PSI, maybe. I get sick of ...

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  1. #31
    Banned Witworth's Avatar
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    Yep, I was going to say fit some air valves / caps in the forks. Like 8 to 12 PSI, maybe. I get sick of suggesting air caps, because you have to hear all the same dumb criticisms from guys who have never used them. I've never, ever, had a problem using them.

    The dead guy I knew who raced T's used Krober ignition units running on the end of the crank. Krober ignitions are like arc welders, but in a good way, not just burning holes in pistons.

    Danger, is my business."

  2. #32
    Senior Member Ravivos's Avatar
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    Tom, Are you kidding? your information is golden! everything you write here, present here with pictures, or give your opinion, is based on actual racing experience, and i truly appreciate you sharing this information.

    Tom, WW, can you further elaborate on the air caps for the forks? how does it changes the feel/damping/steering?
    Tom, any recommendation for good springs on the front?

    If i understand correctly, a single rotor can be a bit lacking in braking force, do you recommend going with twin thin (light) rotors?

    haven't to the engine yet, trying to get the proper parts for proper handling first... then will start thinking about engine modification.

    thanks a lot man!

  3. #33
    Senior Member TrialsRider's Avatar
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    Follow the advances made by modern technology:
    Staying with a single disk and increasing the area and number of active pucks in your brake callipers, will be far more performance oriented then doubling up on mediocre brakes.

    <- This

    Blows away this ->

    With very little increase in weight.
    And you will immediately feel the difference at the lever, with stronger and far more controlled braking.


    Discs can be drilled or slotted to lighten them, but making discs thin in profile is rarely a viable option.


    There are 2 ways to brace RSU forks, either with a brace attached above the wheel (old tech), or a larger diameter/stronger front axle.
    Both work, but the bigger stronger axle works better and results in a huge wheel bearing spec upgrade.

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  5. #34
    Banned Witworth's Avatar
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    Quote Originally Posted by TrialsRider View Post
    Follow the advances made by modern technology:
    Staying with a single disk and increasing the area and number of active pucks in your brake callipers, will be far more performance oriented then doubling up on mediocre brakes.

    <- This

    Blows away this ->

    With very little increase in weight.
    And you will immediately feel the difference at the lever, with stronger and far more controlled braking.


    Discs can be drilled or slotted to lighten them, but making discs thin in profile is rarely a viable option.


    There are 2 ways to brace RSU forks, either with a brace attached above the wheel (old tech), or a larger diameter/stronger front axle.
    Both work, but the bigger stronger axle works better and results in a huge wheel bearing spec upgrade.
    As usual TrainerWheels is off the pace.

    You can't fit much bigger fatter axles to old forks and hubs: they just won't fit, period. Not enough meat.

    The Honda race team has thinned stock discs and won Daytona once, and I guess Mr.H knows his stuff.

    Telefix and Tarrozi style fork braces work just fine on older bikes. They make old forks feel much more rigid.

    A twin piston brake caliper will work just fine on a GT. Modern multi piston calis are fitted so longer pads can be used on narrower diameter braking surfaces on the discs. It's not all about increasing brakepad loading when braking, by having more pistons.

    A single disc works fine on a race track, so rule out twins on a street bike.

    Danger, is my business."

  6. #35
    Senior Member Farmer_John's Avatar
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    Touching on the air fork thing.

    The area of your forks that don't contain oil, springs or damper rods contain air. oil, a liquid, does not compress (much). Air on the other hand does. Even without adding extra to the forks, the air at atmosphere compresses as the fork goes through it's motion and acts as springs and as it compresses increases it's spring rate exponentially.

    By adding a few PSI through a cap mounted valve, you're increasing the initial spring rate of the air in the cavity. It's an easy way to increase the spring rate.

    Alternately, you can increase the level of oil in the forks (again in small increments, the oil has to have some air to compress or you'll lose travel to the point of hydrolock) to increase the progressive action of the air in the forks.
    Ravivos likes this.

  7. #36
    Senior Member Diamondj's Avatar
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    GS1100 disc is a bolt on and is lighter. The hub should be drilled and tapped on both sides and was used on pretty much all the GT Suzukis - 250 up to the 750. Calipers - the EX500 is popular for race bikes as it's legal. Look at GSXR 4 pot calipers but keep in mind you will need to make an adapter plate for the caliper and you may need to play with the rotor and caliper spacing. Some of the 4 pot calipers will hit the spokes when centered on the rotor. Braided line, good pads for the disc, and I am also a big fan of Brembo master cylinders.

    GT750 forks will work in the stock GT500 triple clamps as will GT550 forks. The GT750 forks are roughly 1-2 inches longer than the GT500. GT550 forks are the same length to 1 inch longer. You will want to internally shorten the fork if you want the fork tops flush with the triple clamp. Be careful about raising the front of the bike as the handling will gets really bad at speed if you raise the front without raising the back. The 550 & 750 forks will accept a cartridge emulator and progressive makes replacement springs for them. The damper rods in the GT500 forks are a different design and cannot be easily modified.

    Central Wheel Components in the UK can supply alloy rims and stainless spokes. Switching to an 18" rim up front will make the bike handle better. 2.15 front and 2.50 rear. You can use a 2.50 on the front as well. Tom gave you good advice on the tire sizes. No more than a 100 width up front and a 110 in back. Otherwise you will slow the steering and the bike becomes much less responsive.

    All Balls makes a tapered bearing kit that fits the Suzuki GT's - kit number 22-1005. You may need to grind a lip on the stem for the upper bearing - it will depend on the stem in your GT.

    BTW - My race bike uses a single disc and it is sufficient. I have known a couple of people that raced T500s with dual discs and a few of them switched back to single disc after some near stoppies under hard braking. For a street only bike, dual discs may be the way to go as panic stops are more likely. It will depend on your comfort level I suppose.
    Last edited by Diamondj; 07-28-2015 at 09:14 AM.

  8. #37
    Banned Witworth's Avatar
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    If you run more than about 18PSI of air in forks ( measured: static, extended, with the wheel off the ground ), you will probably blow the seals out when you hit a bump.

    Danger is, my business."

  9. #38
    Senior Member TrialsRider's Avatar
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    Everything works fine until it becomes obsolete dude.

  10. #39
    Senior Member TrialsRider's Avatar
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    Quote Originally Posted by Farmer_John View Post
    ... the oil has to have some air to compress or you'll lose travel to the point of hydrolock....

    and then POP goes your fork seals

  11. #40
    Banned Witworth's Avatar
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    Quote Originally Posted by TrialsRider View Post
    Everything works fine until it becomes obsolete dude.
    Obsolete still seems to work just fine:

    Molnar Manx.

    Name:  Norton-Molnar-Manx-Replica-2013-FF23-11-1024x768.jpg
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Size:  173.7 KB

    The chances of you ever catching one of these with anyone I know racing it:

    0.

    Ooog - gaah! Ooog - gaah!

    Danger is, my business."
    Last edited by Witworth; 07-28-2015 at 09:34 AM.

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