Big bore for Terra Moto TDX-125F '13?

Discussion in 'Ask the Tech Masters???' started by Nghtshr, Feb 20, 2017.

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  1. Feb 20, 2017 #1

    Nghtshr

    Nghtshr

    Nghtshr

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    We like to find a big bore for this engine, buy which engine is it? The mark/code near the front sprocket is 156FMI on the bike model Terra Moto TDX-125F '13 by Thumpstar. Looking for +/-150cc cylinder on Internet, help is welcome, searching for 156FMI on Ebay gives [​IMG][​IMG][​IMG]very different looking big bore cylinders.

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  2. Feb 22, 2017 #2

    motodevo

    motodevo

    motodevo

    Miniriders OG Master Spanner Spinner

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    The problem with putting a big bore kit on that engine is the clutch won't cope. The clutch on pretty much all chinese engines up to 125cc is on the end of the crank, called a primary clutch(ie clutch spins as fast as the engine,one revolution of the crankshaft = 1 revolution of the clutch). For anything bigger/more powerful the clutch is gear driven off the crank at a reduced ratio, a secondry clutch (ie the clutch only spins at maybe 1/4 of the speed of the crank). The reason for this is there is only so much power you can put through a primary clutch before it goes boom (and possibly fly through the cover and take your foot out at the same time).
    TB used to do a 146cc bore kit for 125cc motors but by the time you buy the kit and work out how to stop it killing clutches you could have bought another motor that will easily outlast your built up motor. Your cheapest option is to buy a s/h pitty with a bigger motor, swap out motors between the two and recoup at least half selling new bike with the 125 in it. Dont be fooled different looking clutch case or by the terra moto on the clutch adjustment cover, that engine is just a run of the mill 125 from over 10 years ago, i have the same style 125 motor in an old pit pro i bought for $100 a few years back.
    If you are looking for a bore kit measure the head/barrel stud spacing, those motors run the smaller spacing (like a Honda) where most of the newer 125s run wider spacing
    If you're keen to get a bit more out of that engine, a flat slide carb will make if feel a lil faster, and i am pretty sure you can fit a z40 cam if you take the bearings off the z40 and use the ones on the cam currently in your motor
     
    Last edited: Feb 22, 2017
  3. Mar 11, 2018 #3

    125terramoto

    125terramoto

    125terramoto

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    you cant find anything to fit these bikes anymore but good luck bud
     

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