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  1. #1
    Senior Member Turtle Chaser's Avatar
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    Have some questions for you gear heads. I will be fixing the base gasket leak on my '07 this winter. I could just do a re-ring but how about boring it out as big as it will go with maybe one bore left for safety ? How thick is that cylinder liner and how many oversize pistons are available? Can I gain 5 or 10 cc with boring the stock liner? Also if I re-bore shouldn't I also do a valve job? That would be OK with me as I could do a minor port and polish job while the head was down. I don't have a lot of money but like working on motors. I also don't want to pump it up too much and loose any reliability but I'm thinking a few more cc's and a little better flow can't hurt. I also want to keep it simple, so what do you guys think? Your advice will be greatly appreciated.
    GOD BLESS & RIDE SAFE, TC____________ BC rides: Honda SL100, Honda TL125, Penton125 ISDT, KTM400 ISDT

    now riding '06 TW w/ Jimbo Window, Acerbis bushbusters, ProTaper bars w/risers, Pro Grip 737's, Osram Rally headlamp w/modulator, turn signal beeper, Kenda k270 4.00 x 18,
    triple horns w/relay, big pegs, folding shifter, tuned carb w/drilled slide, 15/50 w/D.I.D. O-ring, RedLine 20w/50, Sterns w/extra padding, extra LED brake light, xt225 brake arm, rear Cycle Racks w/hacked milk crate. Hidden Content

  2. #2
    Senior Member christddel's Avatar
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    Quote Originally Posted by Turtle Chaser View Post
    Have some questions for you gear heads. I will be fixing the base gasket leak on my '07 this winter. I could just do a re-ring but how about boring it out as big as it will go with maybe one bore left for safety ? How thick is that cylinder liner and how many oversize pistons are available? Can I gain 5 or 10 cc with boring the stock liner? Also if I re-bore shouldn't I also do a valve job? That would be OK with me as I could do a minor port and polish job while the head was down. I don't have a lot of money but like working on motors. I also don't want to pump it up too much but I'm thinking a few more cc's and a little better flow can't hurt. I also want to keep it simple, so what do you guys think? Your advice will be greatly appreciated.


    Hello,

    If this can be useful..!

    I have these measures ...




  3. #3
    Senior Member Turtle Chaser's Avatar
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    Thank you kindly christddel, it is very useful. I am trying to find a 70mm Wiseco piston kit but even their website says they aren't currently available? I thought they were common as corn dogs, hmmm. Maybe I'm doing the search improperly?
    GOD BLESS & RIDE SAFE, TC____________ BC rides: Honda SL100, Honda TL125, Penton125 ISDT, KTM400 ISDT

    now riding '06 TW w/ Jimbo Window, Acerbis bushbusters, ProTaper bars w/risers, Pro Grip 737's, Osram Rally headlamp w/modulator, turn signal beeper, Kenda k270 4.00 x 18,
    triple horns w/relay, big pegs, folding shifter, tuned carb w/drilled slide, 15/50 w/D.I.D. O-ring, RedLine 20w/50, Sterns w/extra padding, extra LED brake light, xt225 brake arm, rear Cycle Racks w/hacked milk crate. Hidden Content

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  5. #4
    Senior Member lizrdbrth's Avatar
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    IIRC Wiseco lists the pistons as YFM200 items.



    I can explain it to you, but I can't understand it for you.

    Powdercoated '87 frame, extended swingarm, YZ fork legs, ATV tire, 14/55, XT350 tank, spliced quick-release seat, disc brake conversion, beeg headlight, beeger rack, Lizrdcooler, Lizrdventz and bunch of other stuff all covered in invisible ink.

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  6. #5
    Senior Member Turtle Chaser's Avatar
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    Ok I think I'm getting this sorted out a bit. I found Wiesco pistons for the YFM/YTM 200 &225. The biggest 200cc piston is 68mm and the 225cc piston is available in 70mm. I did my my searching and read that 70.5 would be max safe overbore although I would think 70mm would be safer. I also found posters saying we can use the 225 piston w/no problem and several more saying no way Jose'. So I' still confused on that issue. I don't want to go over Wiseco's advertised 10.25 to 1 compression ratio and I''m thinking I might with a 70mm bore and 225 piston? Can we use a stock Yamaha 70mm 225 piston of some sort to get compression of around 10 to 1ish? Then which head gasket to use? I also read Ben Parry posts concerned with proper head gasket sealing. This is starting to seem not so simple after all. But I'm hoping to get some expert advice from you all soon.



    thank you kindly, mac
    GOD BLESS & RIDE SAFE, TC____________ BC rides: Honda SL100, Honda TL125, Penton125 ISDT, KTM400 ISDT

    now riding '06 TW w/ Jimbo Window, Acerbis bushbusters, ProTaper bars w/risers, Pro Grip 737's, Osram Rally headlamp w/modulator, turn signal beeper, Kenda k270 4.00 x 18,
    triple horns w/relay, big pegs, folding shifter, tuned carb w/drilled slide, 15/50 w/D.I.D. O-ring, RedLine 20w/50, Sterns w/extra padding, extra LED brake light, xt225 brake arm, rear Cycle Racks w/hacked milk crate. Hidden Content

  7. #6
    Senior Member lizrdbrth's Avatar
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    Bear in mind compression ratio will increase a bit due to the overbore itself.



    I can explain it to you, but I can't understand it for you.

    Powdercoated '87 frame, extended swingarm, YZ fork legs, ATV tire, 14/55, XT350 tank, spliced quick-release seat, disc brake conversion, beeg headlight, beeger rack, Lizrdcooler, Lizrdventz and bunch of other stuff all covered in invisible ink.

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  8. #7
    Senior Member Turtle Chaser's Avatar
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    Quote Originally Posted by lizrdbrth View Post
    Bear in mind compression ratio will increase a bit due to the overbore itself.


    Thanks lizrdbrth. That is exactly what I was thinking. I don't want to loose any reliability. I'm trying to find out if the YTM/YTF 225 factory piston is a drop in? They look a bit dished. I think that would help keep the compression ratio more reasonable than the Wiseco.
    GOD BLESS & RIDE SAFE, TC____________ BC rides: Honda SL100, Honda TL125, Penton125 ISDT, KTM400 ISDT

    now riding '06 TW w/ Jimbo Window, Acerbis bushbusters, ProTaper bars w/risers, Pro Grip 737's, Osram Rally headlamp w/modulator, turn signal beeper, Kenda k270 4.00 x 18,
    triple horns w/relay, big pegs, folding shifter, tuned carb w/drilled slide, 15/50 w/D.I.D. O-ring, RedLine 20w/50, Sterns w/extra padding, extra LED brake light, xt225 brake arm, rear Cycle Racks w/hacked milk crate. Hidden Content

  9. #8
    Senior Member lizrdbrth's Avatar
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    They are dished. Advertized c/r is 8.25. They offer them in 10.25 as well.



    Standard bore for all the 225's and 230's is 70mm.If you want to keep compression in the nines, what you want is a standard bore 70mm TTR225/ttr230/XT225/YFM225 et al piston. More or less flat-topped, no dome.



    214cc's with the TW stroke. Too thin on the walls for my taste. I'd want the 225 cylinder, but you'd have to expand the case mouth, and if you stsrted with a used cylinder you'd probably have to freshen it up to at least 70.5.



    I can explain it to you, but I can't understand it for you.

    Powdercoated '87 frame, extended swingarm, YZ fork legs, ATV tire, 14/55, XT350 tank, spliced quick-release seat, disc brake conversion, beeg headlight, beeger rack, Lizrdcooler, Lizrdventz and bunch of other stuff all covered in invisible ink.

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  10. #9
    Senior Member uktw125's Avatar
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    My personal thoughts on this are, unless you are going to use a long stroke crank from a 225 engine with your over bore then it will not be worth the expense or trouble. It's the increased stroke that gives the extra performance more than anything.



    Sorry if I sound like a killjoy but I don't think you will be happy with end result.



    It's your choice though.

  11. #10
    Senior Member Turtle Chaser's Avatar
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    Quote Originally Posted by uktw125 View Post
    My personal thoughts on this are, unless you are going to use a long stroke crank from a 225 engine with your over bore then it will not be worth the expense or trouble. It's the increased stroke that gives the extra performance more than anything.



    Sorry if I sound like a killjoy but I don't think you will be happy with end result.



    It's your choice though.




    No need to apologize for killing my joy, I appreciate all of your advice! Since I must tear down the the top end to replace the base gasket it wont be much more trouble to bore my cylinder and start fresh rather than just re-ring it. The question is how big and what piston? It will be a more expensive route, how much depends on which piston and where I get it from. My major motivation is the old adage 'there is no replacement for displacement'. Willing to spend a bit of money but not willing to pull the engine and split the cases I see this as my opportunity. I do not disagree with your long stroke preference, but in my case I will be retaining the stock exhaust, carb, airbox, ect. So would not a short stroke big bore engine retain the factory power band characteristics and piston speed? I am concerned that a 70mm bore would be to thin for the tw200 liner although I have seen it suggested by some to be fine. Hope for some more input on that one and which head gasket to use with a 70mm piston, tw200 or xt225 ?



    thanks for all the help so far, keep it coming

    regards, mac
    GOD BLESS & RIDE SAFE, TC____________ BC rides: Honda SL100, Honda TL125, Penton125 ISDT, KTM400 ISDT

    now riding '06 TW w/ Jimbo Window, Acerbis bushbusters, ProTaper bars w/risers, Pro Grip 737's, Osram Rally headlamp w/modulator, turn signal beeper, Kenda k270 4.00 x 18,
    triple horns w/relay, big pegs, folding shifter, tuned carb w/drilled slide, 15/50 w/D.I.D. O-ring, RedLine 20w/50, Sterns w/extra padding, extra LED brake light, xt225 brake arm, rear Cycle Racks w/hacked milk crate. Hidden Content

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