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  1. #1
    Join Date
    Nov 2007
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    Default Blueprinting A Go Kart Engine

    I think there are a couple of blokes on this forum with go karts. I just bought myself a used Arrow AX9 rolling chassis. I've decided to put a new Yamaha KT100S engine on it, rather than a used blueprinted engine of unknown history. As I won't be racing the kart (I just want to re-live my childhood) I don't need the extra 1 to 2HP that blueprinting gives. However, if I can do some blueprinting myself, it might make a fun project.

    Have any kart owners on the forum blueprinted their own motors? If so, how much can be done in the home workshop? I have a Hercus 260 with milling attachment, so no doubt there will be limits to what I can do.

  2. #2
    Join Date
    Dec 2007
    Location
    Sydney
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    395

    Default Blueprinting

    Quote Originally Posted by jack620 View Post
    I think there are a couple of blokes on this forum with go karts. I just bought myself a used Arrow AX9 rolling chassis. I've decided to put a new Yamaha KT100S engine on it, rather than a used blueprinted engine of unknown history. As I won't be racing the kart (I just want to re-live my childhood) I don't need the extra 1 to 2HP that blueprinting gives. However, if I can do some blueprinting myself, it might make a fun project.

    Have any kart owners on the forum blueprinted their own motors? If so, how much can be done in the home workshop? I have a Hercus 260 with milling attachment, so no doubt there will be limits to what I can do.
    I used to run one of these at Phil Wards mid week mayhem at Oran Park.
    30 plus guys most over 50 trying to kill each other on the track.
    It wasn't strictly to the rules so some of the heavier guys had very hot karts.
    They made me carry about 20 kg to even things up.
    I ended up casting stuff like sprocket guards and engine mounts in gunmetal at TAFE
    I had an old motor but when I bought a new one I got Bede to blueprint it as I went in a few open meetings.
    If you do mod your motor you may have trouble selling it later.
    I guess you would be matching the ports and smoothing them for max flow also checking port height etc.
    In open meetings all this is not on,the motor is meant to be as produced.
    I was offered a better one for quite a few more dollars when I bought mine.
    Apparently they open them up for a look and then reseal the carton
    I did buy a yank book at one of the auto bookshops re mods I'll see if its still around.
    H
    Jimcracks for the rich and/or wealthy. (aka GKB '88)

  3. #3
    Join Date
    Aug 2008
    Location
    Adelaide
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    68
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    1,373

    Default

    If it's a brand new KT100S then I'd suggest running it stock initially to let everything settle down before you start playing with it. If you do decide to blue-print the engine later you need to decide whether you are ever going to race it under the AKA rules or if you want to sell it to someone who will be as they are quite strict on what you can do to the engine whilst remaining legal.

    Blue-printing the KT is a matter of making sure that the cylinder is square to the crank axis, cleaning up any casting flaws (a touchy area with the scrutineers), adjusting the port heights and cc-ing the cylinder head and fine-tuning the squish band. The Walbro carby is a candidate for fine tuning as well.

    Some of the work requires specialised fixtures (ie to hold the crankcases in a lathe to machine the face where the cylinder sits) and you need to be able to split the crank halves and put them back aligned properly. The bloke I build Superkarts with does KT100S blueprinting with an extremely old, small, Hercus lathe but (a) he has expensive fixtures to make the job possible and (b) he has 40 years experience doing the work - the latter being the most important part.

    Personally, if it's just a "hack" kart I wouldn't bother, the increase in power is minimal and result in tenths of a second improvement in lap times when driven by experienced racers. If you don't know what you are doing you can quite easily turn your KT100S into a dog of an engine.

    You are more likely to get measurable lap time improvements by playing around with the carby tuning, exhaust flex length and then fine tuning the chassis settings, seat position, wheel alignment and tyre pressures.

  4. #4
    Join Date
    Nov 2007
    Location
    melbourne australia
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    Default

    Quote Originally Posted by Gavin Newman View Post
    ... the increase in power is minimal and result in tenths of a second improvement in lap times when driven by experienced racers.
    That's good to know thanks Gavin. I won't touch it in that case.

  5. #5
    Join Date
    Aug 2008
    Location
    Adelaide
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    Default

    Quote Originally Posted by jack620 View Post
    That's good to know thanks Gavin. I won't touch it in that case.
    Good idea.

    You'll be busy enough playing around with all the other variables:

    On the chassis alone you can play with:
    • Ride height, front / rear
    • Castor
    • Camber
    • Toe-in / Toe-out
    • Ackermann or non-ackermann front end
    • Track front / rear
    • Axle softness
    • Front / Rear / Side bars in or out
    • Seat height and position
    • Side pods tight or loose
    • Rear crash-bar tight or loose
    • Tyre pressures
    • Long hubs, short hubs


    There's more time to be found there than in a blue-print for a newcomer and bear in mind that this all changes depending on the track conditions.
    When it comes down to it, the driving is the most important factor, especially in a low powered engine like the KT100S, even more so with the J motor.

    I've been racing sprint and superkarts for the best part of 20 years and I'm still learning the chassis setup changes so you have plenty ahead of you.

  6. #6
    Join Date
    Nov 2007
    Location
    melbourne australia
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    3,228

    Default

    Sounds like I'm going to be busy!
    Chris

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