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2T problem - Vibration at high revs

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by blackjacket, Oct 28, 2008.

  1. Hi guys,

    recently I've been feeling that my bike's engine has been vibrating more than usual at 8k rpm and above. As in its very noticable around my knees and in the frame under the seat. It also feels like there is a bit less eagerness to jump into the powerband. It's quite subtle though, so I _could_ be imagining it...

    Anyone come across anything like that before?

    BTW my powervalve motor/controller has blown so the valve is in the permanently open position (no torque down low). This hasn't been a problem for the last 16,000 k's though. Plug is about 2500 k's old.

    At the moment I'm planning to pull the fairings off and tighten all the mounts, head/cylinder bolts I can see.

    :? :?: :?:


    Edit: forgot to mention, it's a Cagiva Mito, 125cc single
  2. How many kilometres in total has the bike done?

    I think at around 25 000km they are duefor a crank rebuild.

    You should notice the onset of these vibrations happening lower down in the revs the more you ride, and eventually you'll seize a piston as it slaps around the bore too much.
  3. Bike's done about 23,000 k's (speedo cable was busted for a while). Can I confirm that by pulling the cylinder off and feeling excessive play in the conrod/crank? It had a topend rebuild about 2-3,000k's ago and at the time, the crank felt nice and tight. I believe on this bike, the bottom end is usually done at 30,000 k's.

    Edit, the vibes are now all over the rev range. Managed to limp home, but the bike is now off the road. *sigh* Looks like I'm going to be elbow deep in crankcase guts sometime soon.
  4. Vibes are normally due to stuffed bearings. Hopefully small end otherwise crank rebuild time. But while you're there (and before spending any money) make sure all the engine mounts, exhaust and other bolts are tight!
  5. Rebuild the crank before it blows.
  6. hmmm like what one of the other guys said, check all your mounts and bolts for tightness, but I suspect that the big end has gone. It would be worth checking the free play (measuring rather than by feel).

    From other Mito riders the feedback I have got is to order the parts from the UK yourself (save time & money). When the rebuild is being done, check that your oil pump is set up correctly, and make sure that you keep using the same 2T oil after the rebuild.....stick to a good synthetic :)