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Thread: Vibrating belt

  1. #1
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    Default Vibrating belt

    I've (finally) managed to resurrect the 447 (went out and bought some brand new petrol, and started it on a very weak oil:petrol mix - is this bad?). however the belt vibrates sideways a LOT.



    Different rpms show the difference resonating frequencies



    But I'm sure this isn't good for it. Is the solution to simply tighten it up - shim it a bit more? or do I need an idler pulley?



    Ta

    Toby
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  2. #2
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    Default Re: Vibrating belt

    The oil mix ratio should be 50:1. I would not deviate from this.



    Belt vibration is always there but in different degrees. I get the feeling your engine is not running very well which will lead to extra belt slapping. You should do two things, check and adjust belt tension and investigate your engines rough running.




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    Default Re: Vibrating belt

    if its an old system it may be the pulleys are worn this will mean they do not engage corectly and this will give you problems

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    Default Re: Vibrating belt

    Are you running old nylon pulleys? If so, they are prone to swelling over time - apparently they absorb moisture - this will lead to a mis-match between your belt and the pulley causing the belt to jump and cause excessive vibration. Check for this by wrapping the belt around the pulley and checking to see that the belt stays in mesh all the way round. If it starts to ride up onto the teeth, the pulley either needs re-cutting to size or replacing with a decent aluminium one. I had this problem many years ago - it cost me a lot of busted blades before I found out the reason.



    Kevin

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    Default Re: Vibrating belt

    It's a brand new system from Ken...



    I do agree with Iceman - the engine did seem to be rougher than I remember - any ideas?????



    I'll try tightening it a little bit this weekend see if that works.

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    Default Re: Vibrating belt

    Hi Toby,



    how old is the engine? is it points or electronic ignition?




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    Default Re: Vibrating belt

    I would say pretty old to very old. I have no idea - I got it from a bloke off his microlight. It looks and feels old (eg wires look worn).



    It's points with bosch coils. the bolts tapped into the crankcase holding the coils have mostly stripped the thread from inside the holes!



    I re-did the ignition connections though so they are ok (i hope!)

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    Default Re: Vibrating belt

    Its hard to say what the problem might be without seeing the engine but you could check the usual and do a little bit of maintenance to improve matters.



    Things to check are:



    fuel system - clean

    air filter - clean and oiled

    plugs/caps/HT leads - good condition

    compression - good and balanced

    timing - within tolerance

    points - clean

    max rpm - 6500-6800 (with carb slide fully open)




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