Needle Bearing on Wrist pin Loose?

Discussion in '2-Stroke Engines' started by Russntustin, Dec 2, 2008.

  1. Russntustin

    Russntustin New Member

    I'm in the process of prepping a new engine.....I pulled the head and jug.
    (replacing all the studs, want to clean-out the holes in the case)
    Anyway....I see that the needle bearing on the wrist pin just FLOATS back and forth. (with the piston on there) This doesn't seem right. Although I don't see how it's supposed to be 'pinned' or anything. I mean it slides/floats 1/2 way off the piston but not ALL the way off.
    This normal? :helpsmilie:

  2. arceeguy

    arceeguy Active Member

    Yes, it is normal.

    I use a couple of "wavy washers" to help keep the roller bearings and cage centered on the rod. I don't know if it actually helps, but it makes me feel better!
  3. Skyliner70cc

    Skyliner70cc Active Member

    I blame the fact that the bearing can slide back and forth a reason I blew an engine last summer. I had to take a nature break and left my bike on a side kickstand for about 5 minutes while it was idling. I feel that this allowed the bearing to slide out partially which puts an unusual load on it. After my break, I took off and went full throttle down a hill. The bearing cage fell apart and destroyed my top end. I think the bearing was still off to the side when I put a higher load on the engine. This put destructive forces on the race/cage and whamo...instinct engine death.
  4. Russntustin

    Russntustin New Member

    Arceeguy.....Do the wavy washers you put on move also or do they 'squish' on and stay in place?

    Skyliner....Jeeps! So what did you do to fix this??

    Thanks so much for the help!
  5. Mountainman

    Mountainman Active Member

    yes - usually

    a little back and forth doesn't mean much

    it's ANY up and down we wish not to be found

    as we repair that THING
  6. arceeguy

    arceeguy Active Member

    The washers float on the wrist pin like the bearing cage. The cage does still have the ability to shift around, but not nearly as much. Just measure your piston pin diameter (10 or 12mm) and go to your local hardware store.
  7. Russntustin

    Russntustin New Member

    I mean this bearing cage comes half-way out of the con-rod!
  8. Mountainman

    Mountainman Active Member

    cylinder walls

    the cylinder walls should hold that piston THING

    exactly where it is suppose to be

    as we all have fun and ride that THING
  9. Mountainman

    Mountainman Active Member

    side slop or up and down slop

    that's true -- but

    won't it be held in perfect place when in the cylinder ?

    you can use spacers if you wish
    just don't see any reason for them

    maybe I am missing the picture ?

    it's up and down slop that TRULY matters

    love that THING
  10. BSA

    BSA Guest

    I think the problem is that on some kits they don't drill oil holes for the bearings.

  11. Flapdoodle

    Flapdoodle Member

    I was not real pleased to find my roller cage sliding back and forth either. Next time it is apart I will put 2 short lengths of brass tubing on either side.
    Last edited: Dec 3, 2008
  12. Russntustin

    Russntustin New Member

    Well, the piston and con rod will be held in place in the cylinder but that bearing cage still has the ability to shift either way on the wrist pin. My con rod has two oiling holes. This just doesn't seem right but i don't know these things. I will look into the wavy washers. Or the tubing spacers maybe. I'm anxious to get it back together but......:wacko2:

    Sorry for the bad picture....but you can see what I mean.

    Attached Files:

  13. Skyliner70cc

    Skyliner70cc Active Member

    I had to install a new top end and put new bearing in it. I don't idle my engines anymore with the bike on its side kickstand.
  14. Flapdoodle

    Flapdoodle Member

    After some though and the possibility of dropping the short brass tubes I though of earlier into the crankcase, I think this might be better. It would be made from piano wire (spring steel wire) say .020-.032" diameter. It could simply be pressed into place using needle nose pliers.

  15. arceeguy

    arceeguy Active Member

    I'd be afraid that the piano wire would let loose from the heat or reciprocating motion and get caught in a port.

    My only concern with the wavy washers was that the extra weight would throw the engine off balance, but it turns out it doesn't vibrate any more. Chances are, these engines aren't "precision balanced" to begin with anyway. :D

    There is probably no need to do this at all, because even if the bearing is all the way to one side, the rollers are still contacting the entire rod surface. The picture shows something that cannot happen in the engine, and that is having the rod not centered in the piston. I threw the washers on just to make myself feel better.
  16. Russntustin

    Russntustin New Member

    This is what I came up with....(thanks for the idea Flapdoodle!)
    Thanks to all for the help!
    This size brass tubing fits perfectly over the wrist pin. Got it at Ace hardware.

    Attached Files:

  17. Skyliner70cc

    Skyliner70cc Active Member

    You should cut the rest to size and sell the "spacers" to us for 5 bucks shipped :)
  18. heathyoung

    heathyoung Member

    Nice - chopped up on a lathe I assume?

    The clearances on these engines are abyssmal - sloppy engineering at its best. I wonder if a longer (wider?) bearing would be a solution as well?
  19. Mountainman

    Mountainman Active Member

    what was that THING falling off ?

    I like your idea -- but I wouldn't want to try that on mine

    we don't wish for our THING to fall off at high rpm

    she asked "what was that"
    noTHING dear !!!

    ride that THING
  20. arceeguy

    arceeguy Active Member

    It's not "sloppy engineering" - the engineering is what it is. Sloppy fit and finish? Yes. But remember that for an internal combustion engine to even run, there must be a fairly high amount of precision in the manufacturing. No doubt these engines could be a lot better if more attention were paid to the little details.