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  1. #1

    Any easy way to replace MSX 140 Mag Piston

    As noted in a separate post I purchased two 2003 140 MSX's from a charity. One supposedly good and the other parts (per a mechanic that checked them for the charity). I determined that the mechanic, if any, may not have been Polaris as indicated since the good ski had incorrect plugs, no fuel pressure, rope around shaft, and probably needs TPS. But to the bad ski. Mag cylinder was "chipped) on exhaust port side. View of other posts indicate this was probably fuel starvation issue. I confirmed no fuel pressure (and do not believe it was injector). Cylinder wall feels and looks perfect. I have installed inline fuel regulator, checked pressure & then drained old gas. I have new piston and gasket kit. Questions are:
    1. Is their an easy way to removal or it is taking all exhaust out? I was hoping I could just undo from mag cylinder but that does not appear possible. If not OK. I cannot find suggestions anywhere.
    2. Should I try to hone cylinder slightly? I was not sure since it is nik-a-sil. I have basic hone. Again, it fells perfect.

    I will do other checks - screens, thermostat etc. Have manual with torque's.

    Experience - I have swapped engine XL 1200; replaced piston in SL 750 (and added pump/ rebuilt carbs; It was also purchased bad.); Can do most things on auto....Can read all of your posts with advice. Thanks.


  2. #2
    urugol's Avatar
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    You can't really do it easily without removing the exhaust. The main problem is getting to the cylinder base nuts on the exhaust side is very difficult, and for the extra bit of effort you will have a much better workspace to work with, and less blood will be shed trust me on that one. You can deglaze the nicasil cylinder with a 240 grit flexhone so long as there isn't any scoring you can catch a finger nail on. If everything checks out make sure you measure the ring end gap it should be within factory spec.

  3. #3
    Quote Originally Posted by urugol View Post
    You can't really do it easily without removing the exhaust. The main problem is getting to the cylinder base nuts on the exhaust side is very difficult, and for the extra bit of effort you will have a much better workspace to work with, and less blood will be shed trust me on that one. You can deglaze the nicasil cylinder with a 240 grit flexhone so long as there isn't any scoring you can catch a finger nail on. If everything checks out make sure you measure the ring end gap it should be within factory spec.
    Thanks. I hopefully will get to it during the week. Appears to be no scoring. I was amazed. I will let you know how it goes...

  4. #4
    The breakdown was not bad. The cylinder is almost perfect above the ports. There is one gouge below the intake ports. I presume this makes the cylinder bad even though below compression area? Or does it matter? Piston out and ready to go back together except for cylinder concern.

  5. #5
    Back together and runs fine. Ran for a couple of hours. A little too chilly today.

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