Well, I finally get to see the results of running lean

Discussion in 'Old's Cool' started by willierides, Jan 8, 2011.

  1. willierides

    willierides Been here awhile

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    Finally tore into my 1979 TS250 last night after blowing it up last summer.

    Guess it's passed time to check my dry-side crank seals and verify everything else (timing, air leaks, etc.) are in spec. I knew she was starting to act a little odd, but didn't think it was that bad. Guess it was.

    [​IMG]
    #1
  2. Wolfgang55

    Wolfgang55 Long timer

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    Looks like no oil in the fuel
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  3. supershaft

    supershaft because I can

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    Timing can do that too.
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  4. Tosh Togo

    Tosh Togo Long timer

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    See how the top edge of the piston above that new hole has had material blasted away?...it's detonation that did the damage. It may have been exacerbated by the jetting being off, but the lean condition only set the stage for what followed.

    It squeaked, big-time. :cry
    #4
  5. willierides

    willierides Been here awhile

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    I'm not an expert on catastrophic failures like this. I usually am more proactive, but just kind of rode this old girl too hard, too long without paying her any mind.

    I think straight gas would actually look different and be on the intake side? This is on the exhaust side and appears to me to be a classic case of a very lean condition. Maybe the magneto side seal is gone (my suspicion), jetting could be off (don't think so) or, as said above, my timing may be off (could also contribute to detonation?). When I had it apart at one time I simply marked the ignition "plate" location and re-installed it to where it was originally. That may have been wrong before I took it apart, maybe I didn't get it exactly where it was. Dunno. But I just ordered a SWEET new timing light....digital with a built in strobe tach, etc. Can't wait to play with it!
    #5
  6. Tosh Togo

    Tosh Togo Long timer

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    No need for any timing light, as ring-dings of that era were static-timed with a dial gauge. After gapping the points, there should be a number in the book that lists the points-opening as a distance before TDC, not in degrees. It's measured with the dial-gauge inserted through the sparkplug hole.
    #6
  7. willierides

    willierides Been here awhile

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    Nope. It has "PEI", Pointless Electronic Ignition. Onlyt way to set the timing is with a timing light at 6,000 rpm. The tachs on these bikes are notoriously inaccurate (especially this one, I think, lol). That's why I bought the light that I did, it has the built in tach so I can accurately set the timing at the right rpm.

    I suspect the crank seals have outlived their usefulness.
    #7
  8. concours

    concours WFO for 41 years

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    Wrong. That's a lean melt down without a doubt. No oil would be seizure all around, the crown would not be melted on the exhaust port edge like that.
    #8
  9. concours

    concours WFO for 41 years

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    Wrong. Improper timing on a two stroke will put a hole dead center of the piston, like it was sandblasted through.
    #9
  10. concours

    concours WFO for 41 years

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    Crank seal is a likely candidate, don't forget to check the crab flange/boot for leaks. Base gasket (rare) can do this as well.
    #10
  11. stainlesscycle

    stainlesscycle Long timer

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    timing too far advanced can (and will erode) the front of the piston just like that. it is definitely not an oil issue. could be a lean issue also.
    #11
  12. El Hombre

    El Hombre Banned

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    Could be something as simple as a small piece of shit in the main jet. Not a complete blockage, just a partial obstruction. That'll cause it to run lean.

    It sure was detonating, what with the hole in the piston.
    #12