1. Thanks for visiting The Forums at DirtRider.Net. Please join us and gain access to advanced search functions and other features that will make the most of your time here.[ Do it! ]

no start, no compression

Discussion in 'Dirt Bike Mods & Maintenance' started by whaley, Jul 7, 2005.

  1. whaley

    whaley Rookie
    Member

    Joined:
    Jul 7, 2005
    Messages:
    12
    Likes Received:
    0
    i was riding my bike about 2 days ago and i shut it off to put it away and the next time i went to start it, it wouldnt start. it has new fuel and reeds. does this mean i need a new top end. or give me any suggestions on waht to do


     
  2. Colorado

    Colorado Rookie
    Member

    Joined:
    Apr 2, 2005
    Messages:
    228
    Likes Received:
    0
    If it has no compression it isn't going to start. You better tell us more.

    Is your kick starter swinging down with no resistance?

    Did you pull your fuel line and assure gas is flowing to the carb?

    Did you pull your spark plug, check that it isn't carboned, then ground it to the cylinder with the spark plug lead connected and kick the bike over to be sure you have spark? Don't hold the plug or while while you do that, BTW.

    Is your petcock on?

    Is your kill switch stuck?

    There are a lot of things to check before you pull the top end.
     
  3. whaley

    whaley Rookie
    Member

    Joined:
    Jul 7, 2005
    Messages:
    12
    Likes Received:
    0
    it has spark

    the kick starter will go down by hand

    the kill switch isnt stuck, i dont how it would stick

    i havent pulled the fuel line but when i lean it over the gas runs out

    now can you tell me some suggestions and what it would cost and what i should get for parts
     
  4. twoofeach

    twoofeach Rookie
    Member

    Joined:
    Dec 15, 2004
    Messages:
    108
    Likes Received:
    0
    How did it run before it lost all signs of life? Usually, it doesn't decide it has no compression all of a sudden. When was the last time you replaced the top end? Have you tried a new plug? Have you thouroughly cleaned out the carb? Have you tried a compression test or leak down test? Have you removed the head and/or cylinder to inspect the pistons, rings or cylinder? I would just hate for you to replace the top end if it's still good and find out your problem is somewhere else.
     
  5. Colorado

    Colorado Rookie
    Member

    Joined:
    Apr 2, 2005
    Messages:
    228
    Likes Received:
    0
    Like twoofeach said, running one day and not having compression a couple later isn't what one would expect, and ring wear doesn't happen suddenly while the bike is sitting still. I'd isolate the problem before i started buying parts.

    What do you ride? I ride old air-cooled bikes, and would do a compression check first, then question my head gasket seal --- check head torque --- make sure I screwed the plug back in tight --- things like that. The ports would limit the areas compression could escape. If those things were okay I'd pull the cylinder and check ring clearance --- but losing all compression at once doesn't sound like rings unless they broke, and I don't see them breaking parked in the garage.

    It seems the newer water cooled bikes also have power valves related to the exhaust, but I'm not sure just what they do or if one could stick open and release all compression. Autos with water cooling sometimes have head gaskets go and lose preasure either out to the atmosphere or sometimes between the cylinders and the water sleeve (when they overheat and you can usually smell antifreeze in the exhaust) but I know next to nothing about water cooled 2-strokes.

    Sorry I can't help more.
     
  6. whaley

    whaley Rookie
    Member

    Joined:
    Jul 7, 2005
    Messages:
    12
    Likes Received:
    0
    i took the cylinder head off and the piston and it has a bunch of little dings and chips in the head and the top of the piston so i assume i have to replace the head and piston both gaskets and the piston ring, correct? what would make that happen. i was riding it and it died all the sudden and wouldnt start anymore and hasnt started since so i pulled the head and piston. what should i do?
     
  7. whaley

    whaley Rookie
    Member

    Joined:
    Jul 7, 2005
    Messages:
    12
    Likes Received:
    0
    i also was wondering how that would happen becuase the rod bearing is fine and there is no grooves in the cylinder so the cylinder is still good. all of the damage is isolated to the head and top of the piston. and there is no grooves on the things that go aroudn the crank and it still turns by hand good. so i am wondering what would have caused the piston to go bad. is there somethign wrong with the lower end?
     
  8. KXtrailrider

    KXtrailrider Rookie
    Member

    Joined:
    Sep 12, 2004
    Messages:
    96
    Likes Received:
    0
    I had that happen to me twice. First time it was the rod bearing cage coming apart, bearing still felt good but the cage was breaking up sending pieces through the transfer ports. Second time the electrode broke off the sparkplug and beat the piston and head. Also a freind of mine had a screw come out of his reedcage and it did the same thing. Keep looking until you find the trouble or it will do it again. Good luck. Ed
     
  9. I was riding my 2003 yz 125 the other day and it just died out of nowhere. We noticed it was getting no compression, I can push the kick start down with my hand. I tried to start it numerous times an it wouldn't. We changed the plug, cleaned the carb thoroughly, and made sure it was getting gas and it is. What should I do now? The top end on the bike was just rebuilt.
     
  10. rmc_olderthandirt

    rmc_olderthandirt Subscriber

    Joined:
    Apr 18, 2006
    Messages:
    1,534
    Likes Received:
    8
    Unregistered guest:

    You should have started a new discussion instead of commenting on one from 8 years ago....

    The key here is your "no compression" comment. If you have no compression, the bike will not run. You can try all you want but compression is required for an internal combustion engine to operate.

    The statement that you can push your kick start down by hand is not a good measure. I can start my bike pushing the kick start with my hand. I have to push it HARD, but I can do it.

    If you have noticed that the kick is much easier than it used to be then it is a good indication that you have lost compression. If you are not sure, get a compression tester and use it to see what your compression is.

    I suspect that the top end has siezed. Doesn't matter that it had just been rebuilt, although a failure so early indicates that something else was wrong. It is possible that the top end was put together incorrectly last time (an example would be NOT getting the rings set properly on the pins). The ring gap could have been too tight. It could have been the wrong size piston. Did you rebuild it, or have it done?

    If the top end had been rebuilt properly then it is possible that your jetting is too lean and the piston is overheating.

    Or you could have run the cooling system out of water and overheated the engine.

    When you said it "died out of nowhere" it doesn't help much. Was it on a long sustained full throttle run? Fighting your way up a hill? Putting around at low speeds?

    The bottom line is that no/low compression equals top end rebuild. You might learn more when it is torn down.

    To keep it from happening again you should check your jetting and perhaps your riding style (i.e.: don't hold it WOT for miles down a sand wash.)

    Rod
     

Share This Page