Strange low end vibration on a 2-stroke.

Discussion in '2-Stroke Engines' started by OneLittleVictory, Apr 13, 2014.

  1. OneLittleVictory

    OneLittleVictory New Member

    I'm wondering if anyone has had this problem and knows the cause. I'm getting a low end engine vibration (almost like a shudder) in the throttle range just above idle. Mid to high RPM's warrant smoother running, but when I let off the throttle it falls very rapidly back to idle (much faster than it used to, to the point where I sometimes think it stalled even though it hasn't), and through the range of the vibration for a split second. I noticed this about halfway through a 20-mile ride. Engine is well broken in.

  2. jaguar

    jaguar Well-Known Member

    Try using thinner rubber where the engine connects to the frame.
    Check the frame for cracks.
  3. butre

    butre Well-Known Member

    Ditch the rubber entirely imo, or at least use the hardest rubber you can find. the more solidly it's mounted the more vibrational force it needs to shake.
  4. 074KU

    074KU Member

    These engines are known for having pretty out of true flywheels.. If removing/replacing the rubber doesn't work, possibly a bearing issue caused by the flywheel slogging the cheap Chinese bearings?
  5. OneLittleVictory

    OneLittleVictory New Member

    I would tend to think its a bearing issue over anything else. The frame isn't cracked, its a brand new Gravity that I've only had on the road for about a month... And I don't think its a shock material problem because it didn't happen before. My kit didn't come with any rubber when I got it in 2012. I mounted it straight to the frame of a Giant non-suspension mountain bike and I didn't even have a problem back then. I opted to use heavy duty felt when swapping the engine to my new bike.
  6. 074KU

    074KU Member

    I suggest bearing issues because of this:
    (not me, that is Fred that makes the very awesome Fred Head)

    During my last engine tear down (a brand new never run engine) I found metric f**k tons of alloy swarf smashed in bearing pocket from initial assembly of the engine.
    Last edited: Apr 13, 2014
  7. Fabian

    Fabian Well-Known Member

    If the engine starts to vibrate a heck of a lot more than it used to, but the engine is still running well, make sure that all of the engine mounting nuts/bolts (bolts holding the engine to the frame) are done up tight.

    If the engine mounting nuts/bolts have come loose, then apply Loctite 222 and tighten everything up correctly.
  8. HeadSmess

    HeadSmess Well-Known Member

    why the felt? and reading this thread closely, where did the rubber even come into play?

    anyways. previously, a direct mount, there werent any issues.

    now, with felt "isolation"(i assume) its now acting differently.

    general consensus is that any soft material between engine clamps and frames is more detrimental than beneficial. experience only compounds this belief.
  9. OneLittleVictory

    OneLittleVictory New Member

    Thanks for all the input guys. It turned out to be a broken U-bolt... so much for "heavy duty" :rolleyes7: