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Thread: Mechanic-in-Training

  1. #1

    Mechanic-in-Training

    This is a bit long, but if you are interested in maintenance issues, you
    may enjoy reading it.

    I had a lot of airplane work scheduled for Friday and Saturday. On Friday,
    I replaced the mixture control with an ASC Products vernier control. It
    went in easily, and I recommend using one of the "Unibits" for drilling out
    the panel hole to 3/4 inch. It made a clean hole and was easy to use. I
    routed the cable the same way as the old one and got everything adjusted.
    Hooray, it no longer takes two hands to shut down the engine. Since I was
    alone in the shop, I stopped there even though I had some more tasks.

    On Saturday the shop owner's primary assistant, Mike, was in to do a oil
    change for someone else and to work with me to swap out two cylinders and
    install the Horizon P-1000 digital tachometer. While Mike tended to the oil
    change I started removing the baffles, wiring, hoses, tubing, and anything
    else that was in the way of removing the cylinders. After removing the
    rocker arms I removed all but one nut on the number 2 and number 3
    cylinders. With the oil change finished and Mike and I working together I
    carefully slid cylinder 2 off while Mike kept the piston from slamming down
    against the case. The piston pin slid right out. We checked the cam and rod
    bearing play and did a visual on what we could see. It all looked good, and
    the cam lobes were free of any indications of trouble. I had purchased two
    ECI Freedom Cerminil cylinders. They cost only a little more than
    rebuilding the old ones and they come with pistons and rings installed.
    These should get me another 200 hours when I will do a full overhaul or
    engine replacement. We prepared the new cylinder by installing the gasket
    and pulling the piston out just far enough to install its pin. With me
    holding the cylinder in position, Mike slid the piston pin in and then we
    snugged the cylinder to the case. After installing the nuts finger tight,
    we installed the rocker arms, pushrod tubes, and the pushrods.

    Now it was time to do number 3. The cylinder came out easily, but the
    piston pin had seized in the piston and we had to pound the pin out using a
    hammer and a metal rod. The piston was discolored more than the other one,
    and it was clear that the pin had seized a while ago. This meant that all
    rotational movement was between the rod and the piston pin. I took the
    piston over and laid it over an open vice on some padding and pounded the
    pin the rest of the way out. It was really stuck. The pin had score marks
    on both sides. We examined the rod and found that the end was darkened,
    presumably by heat. This cylinder was the one that had low compression. I
    believe that combustion chamber temperatures increase when there is a lot
    of pressure loss during the power stroke, and the additional heat probably
    led to overheating the piston, which transferred to the rod. I checked the
    rings and cylinder walls and did not find excessive wear or scored walls,
    and the rings looked good all the way around so I am not sure why the
    compression was low. The shop owner rebuilds engines in his shop and has a
    lot of experience with engines, and we will wait until Monday for his
    assessment of the rod. If it needs replacing, he knows who to call to get
    one. One of the pushrods showed signs of scraping the inside of its tube,
    so I also may need a pushrod tube.

    Next came the Horizon P-1000 digital tachometer. This was relatively easy.
    I installed the circuit breaker and connected the power wiring while Mike
    connected the wires to the P-leads on the ignition switch. Up to now I
    hadn't taken a real hard look at the circuit breaker area behind the panel.
    What a mess. I will embark on a process to replace all of the weird
    breakers with the new types so they are all the same. An initial tachometer
    check showed that everything was working, and the installation instructions
    say to run both the mechanical and electronic units at the same time to
    verify operation before actually replacing the unit. So far so good. It
    looks like I will have a used tach available. I recall seeing that someone
    was interested in replacing one, so let me know if that was you.

    While checking under the hood, I also found that the bolt that holds the
    carb heat cable to the valve lever was severely worn, and would have failed
    soon. This control gets exercised at least twice on every flight, so it was
    wearing fast. This means a trip to the aircraft parts store on Monday for
    some AN bolts that I will take home to drill the hole for the cable. I buy
    several bolts, and usually get two or three good ones. Drilling into
    threads is not easy, but is doable using a drill press and sharp bits. I
    would bet that there is a fixture for doing the drilling, but I can
    probably buy a lot of bolts for the price of the fixture. The cable
    attachment is partially hidden when the SCAT tubing is attached, but I
    think that it is a good thing to check when the cowling is off. This was OK
    last August. Something slipped out of place since then.

    Well, if you didn't like long-winded posts then I hope that you would have
    stopped reading this one and deleted it by now. I am learning a lot about
    the plane that may come in handy on a remote airstrip somewhere. I figured
    that a lot of people would be interested in my endeavors, so I am writing
    this to provide some insight into aircraft maintenance. I am enjoying the
    experience and saving a few dollars at the same time. Someday, I may even
    get to fly it again. I also have nine more hours of maintenance time in my
    A&P logbook.

    Blue skies.

    Carl Foster Sundowner 9761L Tucson AZ



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  2. #2

    Mechanic-in-Training

    --- In musketeermail@yahoogroups.com, Carl Foster <carlfoster@c...> wrote:

    <snip>

    > Now it was time to do number 3. The cylinder
    > came out easily, but the piston pin had seized
    > in the piston and we had to pound the pin out
    > using a hammer and a metal rod.

    Don't understand how this can be done, (without splitting the cases)
    without affecting the big end..Con Rod Bearing. Any more info?

    > The piston was discolored more than the other one, and it was clear
    >that the pin had seized a while ago.

    piston will show consequences of seized pin..

    > This meant that all rotational movement was between the rod and the
    >piston pin.

    yup & explains why the small end of the rod is discoloured, due to
    overheating.
    So, have some problems with this rod remaining in service, to say
    the least..Jon

    Blue skies.
    Carl Foster Sundowner 9761L Tucson AZ








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  3. #3

    Mechanic-in-Training

    At 09:42 PM 4/22/2005, jon simik wrote:


    >--- In musketeermail@yahoogroups.com, Carl Foster <carlfoster@c...> wrote:
    >
    > <snip>
    >
    > > Now it was time to do number 3. The cylinder
    > > came out easily, but the piston pin had seized
    > > in the piston and we had to pound the pin out
    > > using a hammer and a metal rod.
    >
    > Don't understand how this can be done, (without splitting the cases)
    >without affecting the big end..Con Rod Bearing. Any more info?
    >
    > > The piston was discolored more than the other one, and it was clear
    > >that the pin had seized a while ago.
    >
    > piston will show consequences of seized pin..
    >
    > > This meant that all rotational movement was between the rod and the
    > >piston pin.
    >
    > yup & explains why the small end of the rod is discoloured, due to
    >overheating.
    > So, have some problems with this rod remaining in service, to say
    >the least..Jon
    >
    > Blue skies.
    > Carl Foster Sundowner 9761L Tucson AZ
    >
    >
    >
    >
    >
    >
    >
    >
    >
    >Join BAC today and be a part of the ONLY Type Club for the Musketeer series!
    >
    >www.beechaeroclub.org
    >
    >
    >Yahoo! Groups Links
    >
    >
    >
    >



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  4. #4

    Mechanic-in-Training

    Oops, I hit the send button before I made the comments.

    Removing the seized piston pin was not a problem except for having to hit
    the pin so hard. With the cylinder off, rotate the crank until TDC. Then
    lift up the piston and you can get a nearly straight shot at the pin. The
    rod bearing was fine, so striking the pin straight on did not put any side
    loading on the rod. That particular cylinder had major ring leakage, which
    allowed a lot of exhaust gasses to get into the cylinder and especially the
    rod end. The discoloration was merely carbon buildup from the blow-by
    combustion gasses. After gently scraping the carbon off, the piston end was
    the same color as its base end. The bearing in the piston end was about
    right for an older engine so all is well. The seized pin has black marks
    around where the lubrication holes are, so my guess is that the blow-by
    gasses made it into the lubrication hole and gradually built up until the
    bearing stopped working.

    The run-in flight is tomorrow morning. The mechanic recommended taking all
    11000 feet of runway and watching the oil temperature and oil pressure
    gauges along with the tach to make sure everything is running steady before
    actually lifting off. Then the idea is to remain within gliding distance to
    the airport for two hours, while varying the engine RPM every 15 minutes.

    Carl Foster


    At 09:42 PM 4/22/2005, jon simik wrote:


    >--- In musketeermail@yahoogroups.com, Carl Foster <carlfoster@c...> wrote:
    >
    > > Now it was time to do number 3. The cylinder
    > > came out easily, but the piston pin had seized
    > > in the piston and we had to pound the pin out
    > > using a hammer and a metal rod.
    >
    > Don't understand how this can be done, (without splitting the cases)
    >without affecting the big end..Con Rod Bearing. Any more info?
    >
    > > The piston was discolored more than the other one, and it was clear
    > >that the pin had seized a while ago.
    >
    > piston will show consequences of seized pin..
    >
    > > This meant that all rotational movement was between the rod and the
    > >piston pin.
    >
    > yup & explains why the small end of the rod is discoloured, due to
    >overheating.
    > So, have some problems with this rod remaining in service, to say
    >the least..Jon
    >
    > Blue skies.
    > Carl Foster Sundowner 9761L Tucson AZ
    >
    >
    >
    >
    >
    >
    >
    >
    >
    >Join BAC today and be a part of the ONLY Type Club for the Musketeer series!
    >
    >www.beechaeroclub.org
    >
    >
    >Yahoo! Groups Links
    >
    >
    >
    >



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  5. #5

    Mechanic-in-Training

    --- In musketeermail@yahoogroups.com, Carl Foster <carlfoster@c...> wrote:

    <snip>

    > Removing the seized piston pin was not
    > a problem except for having to hit the
    > pin so hard. With the cylinder off,
    > rotate the crank until TDC. Then lift
    > up the piston and you can get a nearly
    > straight shot at the pin. The rod bearing
    > was fine, so striking the pin straight on
    > did not put any side
    > loading on the rod.

    I may be missing something here but seems to me that this would put
    a massive side load on the rod for which it is not designed, as well
    as the load being taken up, in the end, by the plain con rod bearing.
    I can't speak to aircraft engine disassembly procedure here, but would
    be interested to read any guidelines (Lyc would be great) that
    recommend this method in removing a piston pin.

    Jon





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  6. #6

    Mechanic-in-Training

    HI Jon,

    That is pretty much the accepted method of doing it. Usually, you support
    the rod just below the pin before driving it out.

    John



    -----Original Message-----
    From: musketeermail@yahoogroups.com [mailto:musketeermail@yahoogroups.com]
    On Behalf Of jon simik
    Sent: Saturday, April 23, 2005 2:58 PM
    To: musketeermail@yahoogroups.com
    Subject: [musketeermail] Re: Mechanic-in-Training




    --- In musketeermail@yahoogroups.com, Carl Foster <carlfoster@c...> wrote:

    <snip>

    > Removing the seized piston pin was not
    > a problem except for having to hit the
    > pin so hard. With the cylinder off,
    > rotate the crank until TDC. Then lift
    > up the piston and you can get a nearly
    > straight shot at the pin. The rod bearing
    > was fine, so striking the pin straight on
    > did not put any side
    > loading on the rod.

    I may be missing something here but seems to me that this would put
    a massive side load on the rod for which it is not designed, as well
    as the load being taken up, in the end, by the plain con rod bearing.
    I can't speak to aircraft engine disassembly procedure here, but would
    be interested to read any guidelines (Lyc would be great) that
    recommend this method in removing a piston pin.

    Jon





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

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  7. #7

    Mechanic-in-Training

    > > Removing the seized piston pin was not a problem except for having to
    > hit the
    > > pin so hard. With the cylinder off, rotate the crank until TDC.

    >I may be missing something here but seems to me that this would put
    >a massive side load on the rod for which it is not designed, as well
    >as the load being taken up, in the end, by the plain con rod bearing.
    >I can't speak to aircraft engine disassembly procedure here, but would
    >be interested to read any guidelines (Lyc would be great) that
    >recommend this method in removing a piston pin. Jon

    Mike Rellihan and I have discussed this off list. There is no suggestion
    in the Lycoming Direct Drive OH Manual for tapping a piston pin out with a
    hammer.

    Pressure applied to the pin while holding the piston is the only way to
    properly extract the pin. If it won't come out with "thumb pressure", then
    one can use a variety of methods to ease its removal. Starting with some
    lube on the inside, some strips of emery cloth wrapped around the pin and
    pulled back and forth to abrade the carbon ring that often forms between
    the piston and the rod on the circumference of the pin, and finally, some
    mechanical means of holding the piston and pressing the pin.

    Mike suggested the time honored method of putting a socket on the piston
    pin, a large socket on the opposite side of the piston, and then a VERY
    LARGE C-clamp to drive the pin out into the larger socket.

    My method involves having fabricating a tool many years ago which is
    patterned off of a tool commonly used on 2 stroke engines. A band of steel
    that will just fit around the piston, 2 holes bored in the band exactly
    opposite each other, one of them large enough for the pin to slide
    through. A large nut is welded to the outside of the band over the smaller
    hole. The band is slipped over the piston and aligned with the pin. An
    all thread bolt is run into the nut, such that it presses against the pin
    forcing it out the far side with no side load on the rod.

    Simple, elegant, and cheap for anyone to fabricate. Ought to be in the
    engine tools of every shop in the business.

    Bob Steward, A&P IA
    Birmingham, AL




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