rings snagging ports on a happy-time?

Discussion in 'General Questions' started by gone_fishin, Sep 23, 2007.

  1. gone_fishin

    gone_fishin Guest

    just lately, it seems like i've seen a rash of inexplicable top-end damage, where the bottom-end, including the top-con-rod bushing, is still finer than fine.

    i put some vibration dampers on my new roller-bearing "70" and what's the first new thing i noticed? an occasional light but FIRM "plink" that could really only be one thing...i think the rings sometimes snag the edge of a port.

    i think i can fix this by ever-so-lightly filing a bevel on the ports.

    discussion? as long as you're nice about it, you can even call me stoopid.

  2. gauge

    gauge Guest

    well did the vibrattion dampers work
  3. gone_fishin

    gone_fishin Guest

  4. Alaskavan

    Alaskavan Guest

    I'd be real careful there Augie. Any messing around in there could lead to trouble. But I guess either you know what you're doing, or someone else will. Good documentation please.
  5. wavygravy

    wavygravy Guest

    you hit the nail on the head there augie ! just ever so slightly chamfer the port edges! i had to do this on all my chinese engined pocket bikes too! now if we could get the manufactures to do the same eh? just a little more attention to detail!
  6. gone_fishin

    gone_fishin Guest

    wavy'...thank you...i have another jug i can experiment with...unfortunately on the back burner for a few days, but i will see what i can accomplish :)

    van, if i take pics, how am i gonna make excuses when i screw it up? :p:lol:
  7. Alaskavan

    Alaskavan Guest

    Start a Dontz thread and noone will find it when they search?
  8. wavygravy

    wavygravy Guest

    good one alaskavan!! hahaha!lol lmao!
  9. Scottm

    Scottm Guest

    Well it's a relief to know I didn't screw my motor up and that there is no lower end damage. You think like me Augi that this was my problem? That's where all the scoring was in my cylinder, just below the ports.
    Now do I have to worry about it happening again with my new head and rings?

    Has Duane been contacted?
  10. gone_fishin

    gone_fishin Guest

    i can only answer that by trying a mod then listening, but i think yes.

    not sure if and how it'll help, but it's 20:1 pre-mix for me until i figure this out.

    (yes, there's a message on his machine, i left it for him even before posting)
  11. OldPete

    OldPete Guest

    I would most strongly suggest you search for Egor's post on cylinder porting. In it you will read where he states that the port edge should be champfered by using a smooth steel rod. Like the shank of a new drill bit. This folds the edge of the chrome plating into the port where the ring edge will not grab it. We are only talking a few .001" of an inch here, nothing major. A cast iron bore should be slightly beveled with a fine file however. Good hard chrome is not easy to file anyhoo.
    Be sure to check the ring indexing pins inside the piston's ring lands. If one of these went missing the ring will rotate, its end will cover the port and catch the edge.
    If upon tear-down you find no signs of the slightest scoring, like a slight polishing at the port edge, I would not suspect the rings catching the port.:cool:
  12. Scottm

    Scottm Guest

    I possibly posess the skill to preform this task, but admit I lack the confidence. I'd almost buy another cylinder before I started taking things apart.
    I'm gonna try and sound smart here. Augi , had the damage you've seen like mine been on newer bikes with newer guys like me? Now after every ride, i get my 14mm socket onto those headbolts. I usually get just a fraction of a turn but I don't ****** down on it like He-Man. all this to ask, can a "loose cylinder" provide enough movement/vibration to allow the snagging, or have you seen it in bikes where the rings have already seated after break in?
    Last edited by a moderator: Sep 24, 2007
  13. gone_fishin

    gone_fishin Guest

    only if too loose, imOpinion...'cruzin's "70" was well-broken in with attention to detail when the damage occurred.

    don't be trying to get more turns, try to maintain tightness. get a small torque wrench if you're not sure about tightness...someone please post the proper head-torque for 8mm studs??? it's here somewhere but i'm swamped this morning.

    i don't believe it's a newness thing, it's more the luck of the draw...

    my original "70" had extensive bushing damage but was otherwise just fine, it could/should have led to ring snagging too, but didn't. yours was fine in lower end but had ring/bore damage.

    i think gap position may have something to do with it, but not enough "scientific" data yet to confirm...more data means more broken engines, so i'd rather not have more, yaknow?

    the "65" i tested & blew up was showing a "slight polishing at the port edge" (thanks pete) on bottom of exhaust port:

    to further this research: when rebuilding, i place the ring gaps towards the rear (intake) side of bore...any more input that would help?
  14. Scottm

    Scottm Guest

    Last edited by a moderator: Sep 24, 2007