Grooving on Yz 125 Piston
  • mymxdream
    Posts: 6
    Hey everyone,

    I have a problem with my piston.

    I rode about one season (April-September) on a fresh top end rebuild.  I didn't ride a whole lot this past season, but I did have enough riding time to have it affect the piston and cylinder.

    When I took the cylinder off the piston I inspected each to see if they were still good, or if they need replacing.  The re-plated cylinder that had one riding season out of it was in good shape; so I don't need to replace this.  My problem comes in with the piston.

    Here's pictures of the piston:

    image

    image
    As you can see there is grooving, this grooving takes place on the whole circumference of the piston.  

    My questions are:
    1. Should I replace the piston with a piston kit and just leave the cylinder?
    2. Should I wait till the cylinder goes and just do a whole new top end?
    3. Should I just leave it and not touch, as this is normal wear on the piston?

    Any replies would be great,
    Thanks.

  • CRWOODS
    Posts: 450
    It's not normal, is there marking on the cylinder too?
  • NZriderNZrider
    Posts: 5,086
    is your airfilter properly oiled and not leaking around the edges? that looks like dirt and grit has been getting through.
    *********************
    Winning is 90% rider and only 5% bike, the rest is luck
  • mymxdream
    Posts: 6
    @CRWOODS
    There is very small scratching that are hard to see, but I mean micro; if you feel the cylinder it feels smooth.

    I always oil my air filter (spray and put white lithium grease to seal it) and after every riding session the air filter gets a cleaning.  Getting dirt and grit through is what I initially thought, but I took a look at the reeds and carb; both spotless. (I clean the carb after every 2 riding sessions)  It might be possible that one of the boots have a small tear in them; I'll inspect this.

    Would you guys recommend replacing the piston?
  • sean
    Posts: 3,671
    I would,
  • NZriderNZrider
    Posts: 5,086
    well I still think it looks alot like grit has got in. very unusual for a piston to be damaged evenly al the way round like that from any kind of seizure
    *********************
    Winning is 90% rider and only 5% bike, the rest is luck
  • Maple Leaf MXMaple Leaf MX
    Posts: 12,823
    Do u ride in the sand??
    Expect to die whenever but dream to live forever

    ..the good times on the old DR board will never be back! RIP!
  • mymxdream
    Posts: 6
    @Maple Leaf Mx

    Yes, I do frequently ride in the sand.

    Thanks to all that replied, I decided to put a new piston in the bike.  This way I'm more safe than sorry.
  • Maple Leaf MXMaple Leaf MX
    Posts: 12,823
    Since u ride in the sand i think bjorns theory of filter not catching everythings true. What filter and oil do u use?
    Expect to die whenever but dream to live forever

    ..the good times on the old DR board will never be back! RIP!
  • Fiona21
    Posts: 2
    Let these girls to show you how proper fun is made of.
    London girls
  • CRWOODS
    Posts: 450
    Whoa this is not the place for proper fun.
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