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912UL Engine vibration on throttle back

in 912 / 914 Technical Questions 12 years ago

  • Re: 912UL Engine vibration on throttle back

    by » 11 years ago

    Even though you say that throttle cables cables seem smooth, it sound as though one of your cables may be dragging slightly. This should become evident if you can connect a Carbmate or similar, and then reproduce the fault.

    I have found that lubricating the cables can make a big difference. Cable lubers can generally be obtained from motorcycle shops and work very well.

    Kev
    Thank you said by: Rodrigo Saldarriaga
      
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  • Re: 912UL Engine vibration on throttle back

    by » 11 years ago

    I have been following this thread closely as I have a vibration issue in the 3000-4500 range during throttle back.

    I have a 912ULS(1100TT)/less that 2 hours on overhauled gearbox/slipper

    Engine installed on a JA Higlander turning an Ivo ultralight Patriot IFA prop(have not dynamically balanced it yet)

    Carbs overhauled and synced

    Engine runs great except for the throttle back vibration, it isn't violent but very annoying. I have heard that the 912ULS has a harmonics issue in this range and that is how it is.

    One thing in this thread that got my attention is the topic of motor mounts. I have the Barry Mounts green dot=hard mounts (supplied by the manufacturer) with less than 2 hours on them. I am wondering if the mounts may be too hard for my engine/prop combo.

    Any input or ideas would be appreciated.

    Thank you,
    Brent Hoskins
    Caldwell, ID
      
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  • Re: 912UL Engine vibration on throttle back

    by » 11 years ago

    You can perform a tap test to see if the mount/rubbers are doing their job to remove the inherent vibration. Rotax has a Service letter on this topic: SL-912-010. The best way is to find a company with a DSS MicroVib II as it can be configured to preform this test.
      
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  • Re: 912UL Engine vibration on throttle back

    by » 9 years ago

    Hi Roger.
    I've been noticing an increasing vibration through the airframe of my 2003 Merlin EZ. My engine is the 912 ul 80 hp. Carb sync is done at idle and at 4000 rpm and is good all the way up to 5000rpm and beyond. I have a new IVO 2 blade 72". 850 hrs on the engine and it is during take-off power (5600rpm) and even at cruice at 5000-5400 rpm. the prop makes sort of a steady "woa" sound during take-off but is strong and willing to perform. I have heard that the slipper clutch could be at fault but do I have a slipper clutch in my engine? My ser. nr is 4404444 and was bought in 2003. Any ideas?
    Andy
      
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  • Re: 912UL Engine vibration on throttle back

    by » 9 years ago

    Hi Andy,
    you'r correct, that engine did not come with an overload clutch. unless it was installed after purchase?
    It sounds like you have a prop tracking issue; make sure each blade is the same pitch and check the tracking of the tips.
    Also having the prop dynamically balanced can make a big difference. I have found some IVO props need a huge amount of weight to get them within 0.05IPS (one blade heavy)
      
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