Piston ring Q...

Discussion in '2 smokers' started by D.T., Jan 11, 2014.

  1. D.T.

    D.T. PITA but useful

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    I pulled the cylinder off my snowmobile today. Noticed some blow by and was going to replace the rings. But I got the whole piston.

    Anyway, the ring gaps were at 7 o'clock and 5 o'clock intake side reference. This does not seem right. I was thinking they should be at 3 o'clock and 9 o'clock or parallel to the crank shaft.

    It's a parts unlimited 2 ring cheapo piston. What position should they be at?

    :ear
    #1
  2. anotherguy

    anotherguy unsympathetic

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    Are the ring ends located by pins?
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  3. stainlesscycle

    stainlesscycle Long timer

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    3 and 9 sounds funny - that would put them in line with the piston pin? 5 and 7 puts the gaps between the intake and transfer ports that sounds right. i can't think of a piston with gaps at 3 and 9 - but i don't do snowmobiles... 3 and 9 would place them right in the transfers?- 2 strokes almost always between the transfer and intake. sometimes smack dab in the middle of the intake...
    #3
  4. D.T.

    D.T. PITA but useful

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    :dunno

    I can get a picture if I get the damn piston pin out. F#$ker won't come out! I heated the piston and no dice. I need to get some threaded rod...

    :fpalm

    Alright, never mind. I got the pin out with some threaded rod. The piston has 2 locating pins at 7 and 5 o'clock. Now I understand.

    Here is a pic of the piston anyway (exhaust side). I need to get a hone for the cylinder now.

    [​IMG]
    #4
  5. stainlesscycle

    stainlesscycle Long timer

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    that's a lot of blowby. can't tell how worn the rings are, but if i saw that piston come out of a bike, i would measure the bore and find that it's probably outta spec and needs the next bore. a hone could make it worse...a hone will take maybe another .0005" off the bore. if it's ovalled or loose already you're fighting a losing battle.
    #5
  6. D.T.

    D.T. PITA but useful

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    I checked the ring end gap and it's around .024" so it's on the high side of .008" to .030". This is already an .020" oversize piston. Maybe I will just use some 240 grit and lightly hone myself to remove as little as possible. I ran the piston up and down in the cylinder with out rings. It's not really tight or loose.

    I just don't want to throw a bunch of money at this thing.
    #6
  7. stainlesscycle

    stainlesscycle Long timer

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    i don't know bore size, so i don't know what the specs are, but that's a pretty big gap for any piston under 70mm... think about this way, if perfect is .008" and you're at .024" that's 3 times the best gap, and only 25% away from worst gap... what's the gap of the rings that were in there and leaking badly?



    i wouldn't try honing with sandpaper....... but if you're deadset on doing it that way, move the sandpaper around the bore, and not up and down. any vertical marks/lines will just leak by your new rings. either way if your bore is not round, it'll blowby very shortly..
    #7
  8. D.T.

    D.T. PITA but useful

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    Piston is 72.5mm and the new rings gap is around .020" or less.

    I'm skipping the hone, I used some 500 grit paper and used a circular motion for the cylinder. $30 and a week wait time?

    Tip #1 Mapp gas and a torch really works well on the top of the piston if you are having trouble installing and removing the piston pin. Expands everything just enough to make it slide in easier.
    #8
  9. concours

    concours WFO for 44 years

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    Is it a Nikasil bore? Or cast iron liner? Nikasil just install new rings, NO hone and enjoy. Did you do a compression test before tear down? Is that a Forged WiseGuy piston? or OEM cast? What sled?
    #9
  10. stainlesscycle

    stainlesscycle Long timer

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    it's not nikasil - he's .020" over so it's gotta be iron.
    #10
  11. concours

    concours WFO for 44 years

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    Well, maybe, I guess. Not to be argumentative, but my RZ350 is 2mm OS, and Nikasil. But, you're PROBABLY right.. :1drink
    #11
  12. anotherguy

    anotherguy unsympathetic

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    If you're RZ is Nicasil it's not OEM. The RZ came with cast in iron sleeves.
    #12
  13. concours

    concours WFO for 44 years

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    You are correct. :D I had it done. I just used that as an example of why I asked a bunch of Q's to the OP.

    Ever mess with these???
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    #13
  14. D.T.

    D.T. PITA but useful

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    :huh

    Yikes. Is that out of a newer Ski Doo?

    I fired up the sled yesterday, ran just fine. So far so good. Non plated cylinder in my old 1987 Yamaha Phazer 492cc.
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  15. concours

    concours WFO for 44 years

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    '05 PowerTek 800 143hp. Failed intake boot, known pattern failure. Cylinder was junk, no core allowed.
    The Fizures run forever, make sure no mouse nests in the cooling shrouds. Windshield don't last long on those though...:clap
    #15
  16. anotherguy

    anotherguy unsympathetic

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    Nah I'm not a sled guy. Wheels only. But I have considered building a stupid fast motorcycle a la Tul-Aris.

    [​IMG]
    #16
  17. joexr

    joexr Banned

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    There are Tularis vids on Youtube.:deal
    #17