• Rotax 277 shakes badly below 4000 rpm

    From Corvid@21:1/5 to Remi Dargis on Tue Jun 30 09:54:13 2020
    XPost: rec.aviation.ultralight

    On 06/30/2020 03:39 AM, Remi Dargis wrote:
    On Tuesday, June 30, 2020 at 12:01:55 AM UTC-4, Corvid wrote:
    On 06/29/2020 03:09 PM, wrote:
    Hi everyone, i am new to ultralights (i was only flying skyhawks
    and warriors until now). i now own Fisher ultralight with Rotax
    277. i never flew it, i never saw it flying and i do not know
    previous owner who actually flew it. when i got the airplane it
    had carb removed but everything else looks in good shape. i put
    carb back and was able to successfully start the engine. engine
    runs nice and smooth at 4000 rpm or above, but when it drops
    below 4000 it starts shaking badly. it runs stable but shakes to
    the point that some screws from the panel shook out. i have read
    that single cylinder 2 strokes shake a lot, but to me it looks
    too excessive. i took a prop off and it runs much smoother
    without it. i am thinking prop may be out of balance? the problem
    is that i do not have any experience or knowledge to tell how
    much vibration is too much on those engines. does anyone know
    how to determine if this vibration is normal?

    There's a link for tech support at https://fisherflying.com/

    The prop could be balanced perfectly, and have the flex or mass to
    interact unfavorably with the engine, engine mount,
    speed-reduction drive. Or anything else.

    my problem is that i don't know how much vibration is consider
    "normal". i am reading online that others are complaining about 277
    shaking, some say this is normal and just a nature of this motor. i
    don't want to start replacing things if this is normal. is there any criteria, anything to determine if this is normal? that shaking
    sounds like "compression vibration" - makes one bang on every stroke.
    or if you turn ignition off at higher rpm, when it starts to wind
    down below 4000 starts banging and does that till the last stroke
    when it stops.

    4000 sure sounds high for banging and shaking. I know what I'd replace
    if that's normal.

    crossposted to rec.aviation.homebuilt , a once-bustling group which
    still has lurkers waiting for questions like this.

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  • From Clare Snyder@21:1/5 to Corvid on Tue Jun 30 15:17:53 2020
    On Tue, 30 Jun 2020 09:54:13 -0700, Corvid <bl@ckbirds.org> wrote:

    On 06/30/2020 03:39 AM, Remi Dargis wrote:
    On Tuesday, June 30, 2020 at 12:01:55 AM UTC-4, Corvid wrote:
    On 06/29/2020 03:09 PM, wrote:
    Hi everyone, i am new to ultralights (i was only flying skyhawks
    and warriors until now). i now own Fisher ultralight with Rotax
    277. i never flew it, i never saw it flying and i do not know
    previous owner who actually flew it. when i got the airplane it
    had carb removed but everything else looks in good shape. i put
    carb back and was able to successfully start the engine. engine
    runs nice and smooth at 4000 rpm or above, but when it drops
    below 4000 it starts shaking badly. it runs stable but shakes to
    the point that some screws from the panel shook out. i have read
    that single cylinder 2 strokes shake a lot, but to me it looks
    too excessive. i took a prop off and it runs much smoother
    without it. i am thinking prop may be out of balance? the problem
    is that i do not have any experience or knowledge to tell how
    much vibration is too much on those engines. does anyone know
    how to determine if this vibration is normal?

    There's a link for tech support at https://fisherflying.com/

    The prop could be balanced perfectly, and have the flex or mass to
    interact unfavorably with the engine, engine mount,
    speed-reduction drive. Or anything else.

    my problem is that i don't know how much vibration is consider
    "normal". i am reading online that others are complaining about 277
    shaking, some say this is normal and just a nature of this motor. i
    don't want to start replacing things if this is normal. is there any
    criteria, anything to determine if this is normal? that shaking
    sounds like "compression vibration" - makes one bang on every stroke.
    or if you turn ignition off at higher rpm, when it starts to wind
    down below 4000 starts banging and does that till the last stroke
    when it stops.

    4000 sure sounds high for banging and shaking. I know what I'd replace
    if that's normal.

    crossposted to rec.aviation.homebuilt , a once-bustling group which
    still has lurkers waiting for questions like this.
    Cokld it be "4 cycling" from running too rich? Could also be prop
    balance but "generally" that does not get better with speed. Being a
    relatively large single it will NOT run "smooth" - but as you say, how
    rough is TOO rough?

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  • From Remi Dargis@21:1/5 to All on Tue Jun 30 17:24:15 2020
    At 4000 it is not bad, it starts banging when it goes below that. At 2000 it feels like every compresion stroke makes a painful bang. I dont even want to run it on idle, afraid somwthing will brake. I wish i could look at another airplane with similar
    motor to compare but there is none around. I was hoping someone has one and can share experience.

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