no compression on my yz250
  • 2strokemadness
    Posts: 9

    is a leaky cylinder base gasket a cause to lose compression?

  • Maple Leaf MXMaple Leaf MX
    Posts: 12,849
    Could be
    Expect to die whenever but dream to live forever

    ..the good times on the old DR board will never be back! RIP!
  • markyrocks
    Posts: 1,353
    I highly doubt it
  • NZriderNZrider
    Posts: 5,154
    a stick piston ring would be the most common cause of compression loss on a 2 stroke IMO
    *********************
    Winning is 90% rider and only 5% bike, the rest is luck
  • masterlinkmasterlink
    Posts: 10,008
    Mapehole tech fail
    image
    herby ur useless. MAPLE 2010
    Suzukidude, shut up. CS 2010
    Yeah der, errone be using no seize CRWOODS 2013

    So forward thinking everything else seems SDRAWKCAB.
  • 2strokemadness
    Posts: 9
    well i just bought the bike, i like old school 2 strokes! the previous owner said he recently rebuilt top end, had ok compression when i bought it, took it out yesterday rode for half the day carefully, when we were getting ready to call it a day i noticed a pinging or rattle and loss of power at top end, look around the cylinder base gasket and noticed ooze on the right side and felt air spitting out, i shut it off and checked it over and tried to restart but little to no compression, not sure what happened
  • 2strokemadness
    Posts: 9
    found out the c shaped metal bracket that holds power valve in place is broke, still wondering if that would cause compression loss and make it not start? any ideas?
  • masterlinkmasterlink
    Posts: 10,008
    PV wont cause compression loss
    image
    herby ur useless. MAPLE 2010
    Suzukidude, shut up. CS 2010
    Yeah der, errone be using no seize CRWOODS 2013

    So forward thinking everything else seems SDRAWKCAB.
  • Maple Leaf MXMaple Leaf MX
    Posts: 12,849
    Stfu
    Expect to die whenever but dream to live forever

    ..the good times on the old DR board will never be back! RIP!
  • NZriderNZrider
    Posts: 5,154
    pull the clyinder apart and have a look and fit new base gasket
    *********************
    Winning is 90% rider and only 5% bike, the rest is luck
  • 2strokemadness
    Posts: 9
    i guess cylinder will come off today so i can see if maybe have a broke ring or something, not sure how much compression i'm supposed to have but i can put it in first gear and push it, should i be able to do that?
  • markyrocks
    Posts: 1,353
    Prolly not
  • NZriderNZrider
    Posts: 5,154
    hell no you shouldnt be able to do that very easily
    *********************
    Winning is 90% rider and only 5% bike, the rest is luck
  • BleedMarshallBleedMarshall
    Posts: 2,600

    Quick math is 14.7 x compression ratio of model year = psi of compression test. That gives you a good estimate, but not exactly what you need, hence why you need to get a base from both compression ratings. My '06 YZ125 has a compression of 8.6:1 - 10.7:1, which equals out to 126.42 psi - 157.29 psi.

    I think you have a bad top end all the way around. A new top end (piston, rings, wrist pin, etc.) and gaskets will run you around $125-$150 depending on where you get it. I would not be surprised to also find that your cylinder has a bad taper and/or out-of-round as well causing a ring to fit bad. What year is the YZ250?

    --------------------

    2006 YZ125
    2006 300 XC-W
    "I do dumb things."
    "God hates a coward."
    "I may not always know, but I'll find the answer."
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    image
  • 2strokemadness
    Posts: 9
    85 yz250
  • 2strokemadness
    Posts: 9
    took the cylinder apart and found that the piston just drops through the cylinder
  • 2strokemadness
    Posts: 9
    it supposedly had a rebuild and only 8 hrs. on new top end, from what i am seeing it's never seen a rebuild! base gasket was put on incorrectly causing a massive air leak, c clip  that holds powervalve in place was broke also, other than that everything looks intact, i am sure cylinder need boring and a bigger piston and rings,
  • markyrocks
    Posts: 1,353
    Ur prolly right
  • ThrottleJunkie
    Posts: 1

    whats up guys new to the site I have a couple questions this bike that I'm looking at to buy is a 94 yz250 but the guy wants $250 for it and it needs a transmission plastic and a top end what should I do dont know anything about yamaha's need help please????

  • BleedMarshallBleedMarshall
    Posts: 2,600
    Yeah. A piston with that much play usually means money must be spent and parts sent to a machine shop.
    --------------------

    2006 YZ125
    2006 300 XC-W
    "I do dumb things."
    "God hates a coward."
    "I may not always know, but I'll find the answer."
    http://www.facebook.com/dirtbikesrock
    http://dirthammers.com/
    http://ryandhackney.wordpress.com/
    https://twitter.com/RyanDHackney
    image
  • markyrocks
    Posts: 1,353
    Throttle you'll prolly get more help if u start ur own thread
  • 2strokemadness
    Posts: 9
    anyone know where to get a gasket kit for that year bike? piston and rings coming from wiseco but cant find gasket set
  • markyrocks
    Posts: 1,353
    Id say ebay
  • 2strokemadness
    Posts: 9
    well got the bike a top end rebuild and a five over bore, runs perfect, just like a 250 should
  • markyrocks
    Posts: 1,353
    Awesome glad we could help.
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