2004 T100 Bonneville A Whine

Discussion in 'Bonneville' started by PlanterJohn, Nov 22, 2025.

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  1. PlanterJohn

    PlanterJohn New Member
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    Nov 5, 2025
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    Fenland
    #1 PlanterJohn, Nov 22, 2025
    My Bonnie has done 25k miles but now it is whining, but not a scream, eminating from under the fuel tank. The noise starts at around 50mph/80kph in 5th gear. It continues even if I slow and change down, then stops after a slow manoeuvre but starts again as I speed up. Any suggestions or do I just run it till it fails and then repair?
     
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  2. joe mc donald

    joe mc donald Joe
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    #2 joe mc donald, Nov 24, 2025
    @PlanterJohn Welcome to the family. The bike may just be cam chain adjusting and needs to settle check the adjuster is not sticking. Do tap the upload a file button and show us all the bike.
     
  3. Robbi18

    Robbi18 Member

    Jun 15, 2025
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    #3 Robbi18, Nov 25, 2025
    That whine is likely your cam chain tensioner. It's a common issue on those Bonnies. The automatic tensioner wears out and doesn't keep the chain tight.

    Don't just run it. If it jumps time, you're looking at bent valves and a massive repair bill. Get it checked out sooner rather than later. A manual tensioner is a popular fix.
     
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  4. PlanterJohn

    PlanterJohn New Member
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    #4 PlanterJohn, Nov 25, 2025
    Thanks for your helpful comments Joe and Robbi. I will put your suggestions to the test over the winter with further investigations and rectification - the ultimate aim for this bike is to affix a sidecar in preparation for the time when I no longer feel safe on two wheels! In the meantime I have a 97 Triumph Adventure and a Zero SR/S to play around on.
     
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  5. joe mc donald

    joe mc donald Joe
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    #5 joe mc donald, Nov 26, 2025
    @PlanterJohn Would like to see the bikes. If you tap the upload a file button bottom right corner you can put a smile on our faces.
     
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  6. MightyBoosh

    MightyBoosh Senior Member

    Mar 29, 2023
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    #6 MightyBoosh, Nov 26, 2025
    Not sure a loose camchain would whine....my fuel pump inside the tank makes an odd noise from time to time, but l don't think a 2004 has one, they're carburated :)
     
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  7. PlanterJohn

    PlanterJohn New Member
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    #7 PlanterJohn, Dec 6, 2025
    Well, after checking the chain tensioner and another ride with the whine coming again so decided to drive on. The noise subsided but I managed to get a better location near the front of the tank. So disengaged the top of the spedometer cable and gave it a squirt of WD lithium. No noise now. Phew. Thanks for the advice.
     
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  8. joe mc donald

    joe mc donald Joe
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    #8 joe mc donald, Dec 7, 2025
    @PlanterJohn Fantastic mate and so happy you got the the source of it. Now your tip is hear for others who might suffer similar. Enjoy your Bonnie and that side car if you fit it.
     
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