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Vibration Only at 5,000 RPM Up and Down

Discussion in 'XJ Technical Chat' started by Cant Register, Jun 25, 2017.

  1. Cant Register

    Cant Register Member

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    I have a vibration only at 5,000 rpm.

    Ridding around, bike runs really good. As I go up in rpm's, it's smooth, until I get to 5,000 rpm. I have a shaking vibration in the motor, with different sound. If I go past, it smooths back out.
    Higher rpm, when I come back down, it's smooth until I get to 5,000 rpm it comes back, then down lower it smooths out. This is very narrow, almost only at 5,000.

    So, I have a vibration with a different sound only at 5,000 rpm, both up and down. Why only at 5,000?

    Thank you,
    Chris.
     
    Last edited: Jun 25, 2017
  2. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    That's normal (if I'm reading you description right). The engine hits the natural frequency at which the frame wants to vibrate.

    There are two things to look at in order to make sure that it's just sympathetic vibration.

    1. Have you done a running synch of the carbs?

    2. Have you made sure that all of the engine mounting hardware is tightened to spec (and that the mounts are in good condition if you have a Maxim)?
     
  3. CanuckXJ

    CanuckXJ New Member

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    I agree with Kmoe, that is just the natural resonance of the motor. Mine does it around 5000-5500 rpm which equates to roughly 105-110 kph on the highway.
     
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  4. Cant Register

    Cant Register Member

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    Thank you for the response. The description is not what I would describe as normal. This just started resonantly. and is bad enough that it makes you think if you left it at 5,000, the motor would blow up. All kinds of clanking and rattling.

    I have not done a running sync of the carbs.

    Haven't looked at the engine mounting hardware to see if it's tightened to spec, but will do that.

    Thank you,
    Chris.
     
  5. CanuckXJ

    CanuckXJ New Member

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    the vbration/drone is normal......clanking and rattling isn't. Time to give the bike a good go through as it sounds like something has worked loose and makes noise once you hit that rpm. I'd be looking at mounts and the whole exaust system, but really it could be anything........license plate, fender, lock chain if you still have it etc.
     
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  6. Stumplifter

    Stumplifter Well-Known Member

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    Agree with the above. My XJ 650 Maxim does a "purr" type vibration right at 5k also.
    Definetly not what I would call a "shaking vibration".

    Check obvious fasteners then if it is still there maybe set her up on the center stand and have a friend bring it up to 5k and check around. A stethoscope or a long screwdriver held to the ear can be a helpful tool. However sounds like your vibration should reveal a recognizable shaking of one or more components.
     
  7. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Thanks for the clarification. Do what those guys above me said. Something is loose or broken.
     
    Last edited: Jun 25, 2017
  8. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    Touch a toe to the chrome heat shield on the sides of the exhaust.....they are often a culprit as the weld breaks and the shield loosens.
     
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  9. jayrodoh

    jayrodoh YimYam Premium Member

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    Check your motor mounts. Mine did the same thing right after I had to pull one of the mount bolts out, I tightened it up and the vibration went away. I suspect the noises you are hearing are loose things rattling when the vibration hits the right frequency. I think that's the term. The heat shield like hogfiddles mentions will definitely rattle when loose.
     
    Last edited: Jun 26, 2017
  10. Cant Register

    Cant Register Member

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    OK, I'll check the suggestions. The rattling is in the motor.
     
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  11. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    .... and a heat shield rattle will sound like the engine is about blow up----
     
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  12. Cant Register

    Cant Register Member

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    Didn't have time to check yet, but did find out another thing. I took it out this morning. When I first started, it didn't do it at ll. As I rode around after about 15 minutes, as the motor heated up, it got progressively worse.
    Cold, and cooler engine, doesn't do it at all. After it gets hotter, it does it more and more, until it's really hot, then it's at what I described in my OP.

    A few times, it sounded like it was coming from the clutch.

    One question. Can a clutch do this?

    Thank you,
    Chris.
     
  13. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    Check your oil then--- smell gassy?
     
  14. jsngrimm

    jsngrimm Member

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    Make absolutely sure it isn't coming from the heat shield, mine did exactly the same thing, horrific noise and vibration right about 5K RPM, and it also kind of sounded like it was coming from the clutch cover. I felt really dumb when I figured out it was the right side heat shield that had broken a weld the whole time
     
  15. XJOE550

    XJOE550 Active Member

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    What model bike do you have Chris? I had a rattle at 4000 rpm. Does it do it when standing still? In other words, when the bike is neutral and you raise the rpm to 5000? I found my problem was a loose shield under the carburetors. That is why I asked what model you have.
     

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