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  1. #1
    Autosport's Avatar
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    Help - GP1200R to 1300 top end conversion

    Pulled the head off my ski today to discover excessive piston movement so pulled the barrels off and found I need to do pistons as well.

    I was looking into doing a 1300 conversion but looks like its come sooner rather then latter, so need some info so I can decide what needs to be done.

    Can the 1200 barrels be bored out to 84mm to fit 1300 pistons (I'm guess you need to sleeve the barrels to do this?)

    What is done with the power valves with the larger piston diameter?

    What needs to be done to the porting of the 1200 barrels to make it work?

    what is done with carby jetting?

    any links one where I can find this info would be greatly appreciated (I'm from Australia so US shops are not really an option.. doing most of the work myself).

    thanks in advance
    Damo
    [email protected]


  2. #2
    Dirty Sanchez's Avatar
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    conversion

    -Bore and re-plate to 1300 piston & check valve clearance -cut if needed
    - do a search on carb jetting for 1300
    - I'll send you some additional info via PM
    -sleeving not recommended due to heat transfer etc... nickle plating used

  3. #3
    philip_gpr's Avatar
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    you have a couple choices

    Option # 1

    Buy new 84 mm pistons

    get your 1200 cylinders bored to 84 mm

    get the cylinders ported to get the ports right

    cylinders then need to be plated with Nicasil

    have 1200 head machined for 84 mm pistons

    add new 84 mm power valves (the 1200 won't work, they can be used if you get them cut properly)

    in the US this is a $2,000 USD excercise (we are fortunate in that we have several good shops that can do porting available, that is the hardest piece to get done right) Getting the head machined properly is also tricky. Most shops won't get it right the 1st time.

    Option # 2

    sell your 1200 parts and buy a complete 1300 top end

    (I would think your 1200 top end is worth somewhere between $700 to $850 USD)

  4. #4
    Autosport's Avatar
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    Thanks guys,

    Philip, you have email.

    thanks

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