FS: Big Bore Kit
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Thread: FS: Big Bore Kit

  1. #1
    Senior Member YBW's Avatar
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    FS: Big Bore Kit

    So I put together this setup for my bike, but now I am considering going a slightly different route. If I can sell these components than great, if not I will just use them on my build. The kit includes the following:

    Yamaha YFB250 Cylinder, bored and honed
    Yamaha 74mm forged piston, 9:5:1, skirt milled to clear crank/balancer
    Yamaha piston rings for above piston
    Tusk gasket kit for cylinder

    All parts are new (except for the cylinder of course). This will up your displacement to 239.6cc if you are running a stock TW motor, and 249.4cc if you are running a 58mm stroke (like in a TTR motor, etc.). If you are running a TTR or XT motor, than it is a bolt on upgrade. Those running a stock TW motor will have to open up the case mouths to accept the larger cylinder sleeve. If you want a new Yamaha wrist pin and clips I can provide those as well at an extra cost. Price is $325 plus shipping.

    Thanks

  2. #2
    Senior Member lbxr's Avatar
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    This is very tempting....Any interest in taking a new 71mm Wiseco 10.25 to 1 piston kit as a partial trade? I have 2 extra piston kits....

  3. #3
    Senior Member YBW's Avatar
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    Sorry lbxr, I'm not in need of one of those at the moment. I would take it in trade to help you out but I already have too many parts I don't have time to sell!

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  5. #4
    Senior Member BkCntryCrwlr's Avatar
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  6. #5
    Senior Member YBW's Avatar
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    Quick FYI: The new Yamaha wrist pin and clips I will include for $15, and shipping to the continental US is right around $20 depending on where you are.

  7. #6
    Senior Member lbxr's Avatar
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    Quote Originally Posted by YBW View Post
    Sorry lbxr, I'm not in need of one of those at the moment. I would take it in trade to help you out but I already have too many parts I don't have time to sell!
    Ok thanks...Curious, which way are you going if you are not using the kit you have for sale?

  8. #7
    Senior Member YBW's Avatar
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    Well, I am rebuilding my crank as part of the build anyway, and it got me thinking about boring the small end of the connecting rod to be able to fit the larger wrist pin (+1mm) newer XT250 and Raptor engines use. Then I could use a piston as large as 76mm (which would be a tight fit if its even possible) and as high as a 13:1 compression ratio. Obviously there is a bit to figure out, but the way I see it is selling the kit I have opens my options back up and if I keep it than I can go the tried-and-true route (nothing to figure out).
    Last edited by YBW; 10-17-2016 at 01:33 PM.

  9. #8
    Senior Member harvey's Avatar
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    Hi YBW

    Would a XT250 cylinder be the same as a YFB ? as i am looking to open out my TTR230 motor before fitting it to my T Dub.

    Regards Barry
    Boys and there toys.
    HondaZ50ak2 , Honda CT70 , Honda ST50 , Suzuki TC120 , Suzuki LTF400 , Nissan Navara D40 , XT225 , 2006 + 1993 & 1989 TW200s. Hidden Content

  10. #9
    Senior Member YBW's Avatar
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    Unfortunately not, as the XT250 bolt holes don't line up and the YFB/YFMs are actually only 229cc from the factory.
    harvey likes this.

  11. #10
    Senior Member YBW's Avatar
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    Item sold, thanks BkCntryCrwlr!

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