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Thread: What do you think could the reason be??

  1. #1

    What do you think could the reason be??

    I have a 1975 B24R Sierra . Several weeks a ao, I had
    to abort a flight because the engine started to run
    really rough and the oil temps when up almost to the
    red. Turns out that the top plug in nr 3 ( aft
    passenger side) had a broken insulator which obviously
    made the engine run rough. That is the background ( or
    maybe that's the beginnning ) here is the story.
    I went flying yesterday and after about 20 minutes ,
    at about 3,500 ft, the engine "hick-upped" lost about
    25 revs for a second or so and then ran fine for a few
    minutes. Than, the engine started to gradually run
    rough again, not too bad at first. I happen to be
    flying with a very seasoned flight isntructor who also
    own a sizable aircraft maintenance shop so we were
    able to keep all the gauges in sight and we were able
    to relate to each other what we saw, heard and felt. I
    noticed that suddenly that the gauge showing rich /
    lean status, which was pegged at 100 degrees rich of
    peak, swung up to pretty well to the red line which is
    where the temperature shows effective totally leaned
    out. I than increased mixture control and enriched the
    mixture to bring the needle back down to 100 degrees
    rich of peak. The engine kept running rough, we
    increased trottle ( maximum revs) and reduced manifold
    pressure to reduce load on the engine and returned to
    base. Oil temp stayed a little higher but we were
    descending at higher airspeed so that would
    potentially not mean anything. Back on the ground the
    engine ran smooth at idle.
    We also checked magneto's in the air ( I have an
    Horizon P 1000) and they worked perfectly , mag drop
    about 20 revs on both left and right magneto.

    I also noticed before the flight ( on the ground
    immediately after starting the engine) that there was
    a slightly "harder" metallic knocking sound for a few
    minutes at the max.

    So , input please. What do you suggest it might be?
    Valve?? cylinder? I believe that the fuel injection
    system is working fine but I am not sure because I do
    not have an engine analyzer installed. My mechanic
    will start looking at the a/c tomorrow and any input
    would be appreciated.

    Thanks

    HarryR



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  2. #2

    What do you think could the reason be??

    From an engineering perspective and not an aircraft mechanic, and knowing
    some probable problems with a/c engines, I would suspect a cracked cylinder
    head that causes a valve to stick. Perhaps exhause or intake of #3 which
    traditionally is the hottest. We had a cracked cylinder head there once
    and never knew it. In talking with several A&Ps, seems it's a common problem
    for excessively leaned out engines. Once the crack develops near the valve
    guide, the guide and valve will lose alignment as the crack opens up and
    increased friction between the valve and guide causes slow return and
    finally no return.

    BTW, same problems were common in Volkswagen engines which I used to rebuild
    in my early days (one per week for 2 years). Only real difference is that
    the heads and cylinders are 2 pieces on the VW and one on our a/c engines.

    Dr Bill
    N9230S
    76 SUndowner

    -----Original Message-----
    From: musketeermail@yahoogroups.com
    [mailto:musketeermail@yahoogroups.com]On Behalf Of Harry Roussard
    Sent: Sunday, May 22, 2005 9:22 PM
    To: musketeermail@yahoogroups.com
    Subject: [musketeermail] What do you think could the reason be??


    I have a 1975 B24R Sierra . Several weeks a ao, I had
    to abort a flight because the engine started to run
    really rough and the oil temps when up almost to the
    red. Turns out that the top plug in nr 3 ( aft
    passenger side) had a broken insulator which obviously
    made the engine run rough. That is the background ( or
    maybe that's the beginnning ) here is the story.
    I went flying yesterday and after about 20 minutes ,
    at about 3,500 ft, the engine "hick-upped" lost about
    25 revs for a second or so and then ran fine for a few
    minutes. Than, the engine started to gradually run
    rough again, not too bad at first. I happen to be
    flying with a very seasoned flight isntructor who also
    own a sizable aircraft maintenance shop so we were
    able to keep all the gauges in sight and we were able
    to relate to each other what we saw, heard and felt. I
    noticed that suddenly that the gauge showing rich /
    lean status, which was pegged at 100 degrees rich of
    peak, swung up to pretty well to the red line which is
    where the temperature shows effective totally leaned
    out. I than increased mixture control and enriched the
    mixture to bring the needle back down to 100 degrees
    rich of peak. The engine kept running rough, we
    increased trottle ( maximum revs) and reduced manifold
    pressure to reduce load on the engine and returned to
    base. Oil temp stayed a little higher but we were
    descending at higher airspeed so that would
    potentially not mean anything. Back on the ground the
    engine ran smooth at idle.
    We also checked magneto's in the air ( I have an
    Horizon P 1000) and they worked perfectly , mag drop
    about 20 revs on both left and right magneto.

    I also noticed before the flight ( on the ground
    immediately after starting the engine) that there was
    a slightly "harder" metallic knocking sound for a few
    minutes at the max.

    So , input please. What do you suggest it might be?
    Valve?? cylinder? I believe that the fuel injection
    system is working fine but I am not sure because I do
    not have an engine analyzer installed. My mechanic
    will start looking at the a/c tomorrow and any input
    would be appreciated.

    Thanks

    HarryR



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  3. #3

    What do you think could the reason be??

    Hi Harry,
    Some easy fixes if you're fortunate would be a leak in the intake manifold
    or a clogged injector.
    John

    -----Original Message-----
    From: musketeermail@yahoogroups.com [mailto:musketeermail@yahoogroups.com]
    On Behalf Of Harry Roussard
    Sent: Sunday, May 22, 2005 7:22 PM
    To: musketeermail@yahoogroups.com
    Subject: [musketeermail] What do you think could the reason be??


    I have a 1975 B24R Sierra . Several weeks a ao, I had
    to abort a flight because the engine started to run
    really rough and the oil temps when up almost to the
    red. Turns out that the top plug in nr 3 ( aft
    passenger side) had a broken insulator which obviously
    made the engine run rough. That is the background ( or
    maybe that's the beginnning ) here is the story.
    I went flying yesterday and after about 20 minutes ,
    at about 3,500 ft, the engine "hick-upped" lost about
    25 revs for a second or so and then ran fine for a few
    minutes. Than, the engine started to gradually run
    rough again, not too bad at first. I happen to be
    flying with a very seasoned flight isntructor who also
    own a sizable aircraft maintenance shop so we were
    able to keep all the gauges in sight and we were able
    to relate to each other what we saw, heard and felt. I
    noticed that suddenly that the gauge showing rich /
    lean status, which was pegged at 100 degrees rich of
    peak, swung up to pretty well to the red line which is
    where the temperature shows effective totally leaned
    out. I than increased mixture control and enriched the
    mixture to bring the needle back down to 100 degrees
    rich of peak. The engine kept running rough, we
    increased trottle ( maximum revs) and reduced manifold
    pressure to reduce load on the engine and returned to
    base. Oil temp stayed a little higher but we were
    descending at higher airspeed so that would
    potentially not mean anything. Back on the ground the
    engine ran smooth at idle.
    We also checked magneto's in the air ( I have an
    Horizon P 1000) and they worked perfectly , mag drop
    about 20 revs on both left and right magneto.

    I also noticed before the flight ( on the ground
    immediately after starting the engine) that there was
    a slightly "harder" metallic knocking sound for a few
    minutes at the max.

    So , input please. What do you suggest it might be?
    Valve?? cylinder? I believe that the fuel injection
    system is working fine but I am not sure because I do
    not have an engine analyzer installed. My mechanic
    will start looking at the a/c tomorrow and any input
    would be appreciated.

    Thanks

    HarryR



    Yahoo! Mail
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    [Non-text portions of this message have been removed]



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    --------------------------------------------------------------------~->

    Join BAC today and be a part of the ONLY Type Club for the Musketeer series!

    www.beechaeroclub.org


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