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You need NZrider or MJP or the like to chip in on this.
Welcome to DR.
Sorry to come in late.
To begin, and using KTM bases pricing, a 2008 144SX piston assembly, rings and all but gaskets, will run you around $160 US on average. The connecting rod (conrod) repair kit will run you around $250 and the complete crank assembly is just over $400, all US prices. You might get lucky and it only needs bearings, which run about $40 each, but unless you have a press and truing stand, you will need a shop to do the repair for you. To be honest, unless you have a case splitter and possibly a crank puller, you are going to have to have a shop do the work anyway. In no way should you try and split cases without a splitter. I have seen people try and do it with other means and end up having to buy new cases, and those are not cheap by any means.
To get to the conrod, you will need to get the top end off, and to get to that you need to remove the tank, radiators (at times), and possibly a few other aspects outside of the radiator shrouds and such. Loosen the head bolts in a star pattern and do not take the nuts off all at once. Release the pressure slowly so you do not warp the head. The same goes with the cylinder (jug) as well. Though it will not warp as easily, if at all, you still need to release the pressure on each nut slowly so you do not damage any threads or the like. Do a good visual check of the cylinder and I suggest you also do a bore and taper check as well to see how it is and if it is in factory spec. or not.
Next, like NZ stated, check for play at the connecting rod. Vertical movement means you need to split the cases, but you need to measure the lateral movement and check it against factory specs to see if the cases need split then to get the conrod assembly repaired or replaced. Chances are that if you can move the kicker then you have not had any damage to the cylinder and such, but that means nothing for the crank. Slow movement by working the kicker with your hand is in no way the same as having that engine working at 4000 RPM and having issues of a bad crank.
Get the service manual and follow what it says and you will be fine. Good luck and keep us posted.
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