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Re: Straight Question ....

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  • George Bearden
    ... What you said is true, though I have never heard of an opposed engine running on the same crank throw. Have you? ... Yes, like BMW and VW. It has always
    Message 1 of 76 , Jun 2, 2008
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      > they both don't move the same direction as they would with
      > an opposed configuration running on the same throw,

      What you said is true, though I have never heard of an opposed engine
      running on the same crank throw. Have you?

      > An opposed engine running on 2 throws, 180 degrees apart,
      > would need to be a larger, heavier engine

      Yes, like BMW and VW. It has always been my understanding that the best
      balanced engine is the opposed engine, with counter-weights. As you
      most all know, the VW doesn't use counterweights. The opposite motion
      of the rods and pistons cancel out much of the vibration from the other
      piston.

      In the VW, without counter weights, the distance between the center of
      the crank throws means that there is a 'rocking-couple' vector trying
      to bend the crank in a horizontal plane. This is anchored at the center
      main. Both sides of the crank are trying to move horizonatally back and
      forth, the center main prevents this. Thus at high rpm in VW's, one
      will see the center main get pounded apart. The advent of the counter
      weighted cranks took away this weakness plus it canceled even more of
      the vibrations.

      This rocking-couple is there in 90 degree engines, but in much less
      magnitude. At one time Harly used a "knife and fork" rod arrangement
      but I know nothing about current Harley). This kept both rods, pistons
      and cylinders on the same plane. Sorta like big radial engines (which
      have a coupla different rod arrangements)

      I once held a Sachs rotary engine in my hands as it ran. SO smooth!

      OT!
      I am building a Suzuki 1600 for my Samurai and I am hogging out the
      ports and also balancing all the small parts as well as I can with a
      bram scale. After this I will have a balance shop finish the balancing.

      GeoB
    • Andy Asberry
      Do you know the location on the crank that broke? Andy ... mounting ... cool ... the ... turn ... on ... pass ... probably ... the ... you
      Message 76 of 76 , Dec 14, 2008
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        Do you know the location on the crank that broke?

        Andy

        --- In Small4-strokeEngines@yahoogroups.com, "harveyking2002"
        <harveyking@...> wrote:
        >
        > GPAS tried the prop on the PTO side of the 25 hp Kohler V-twin and
        > had problems with crank breakage. They solved the problem by
        mounting
        > the wood prop on the flywheel end. This was a pusher install.
        >
        > Dick
        >
        >
        >
        > --- In Small4-strokeEngines@yahoogroups.com, "Dan Moser"
        > <danmoser@> wrote:
        > >
        > > OK, thanks for that answer, Jerry.
        > >
        > > The tractor prop on the flywheel side is a preferable arrangement
        > > because it allows better cooling air flow... it comes in on the
        cool
        > > flywheel side where the air intakes are, and leaves on the hot PTO
        > > side where the exhaust ports are located. Driving the prop with
        the
        > > PTO end is definitely doable, though it does create more of a
        > > challenge to route the airflow properly. Leeon Davis did it that
        > way
        > > with the 16hp V-twin engine on his little DA-11... I wish I knew
        > more
        > > details about what he did and how well it worked.
        > >
        > > I'll definitely go with a fixed pitch wood prop, not adjustable
        > > composite. The goal is to remove most of the flywheel mass, then
        > > match the removed rotational inertia with the prop, hub, and
        > > additional ring weights as needed. This way, the engine should
        turn
        > > over correctly and be a bit lighter.
        > >
        > > Thanks again!
        > >
        > >
        > > --- In Small4-strokeEngines@yahoogroups.com, JERRY <j.soar.aero@>
        > > wrote:
        > > >
        > > >
        > > > My CH25 is a Command Pro. it came with a needle thrust bearing
        on
        > the
        > > > pto end of the crank. I figured that with the pusher
        > configuration
        > > > and mounting the prop on the flywheel, the thrust load would
        pass
        > > > thru the crank to the thrust bearing. I don't know what the
        > factory
        > > > ratings for it would be though.
        > > >
        > > > For your configuration, unless you can find one with a needle
        > thrust
        > > > bearing on the flywheel end, you would either need to add a
        > needle
        > > > thrust bearing yourself, or depend on just the flat surface to
        > deal
        > > > with it. Since Kohler can provide one that way, although
        probably
        > > > hard to find, it suggests that doing the machining either on
        the
        > > > crank, or the back of the case would be quite feasible.
        > > >
        > > > Otherwise you would have to mount the prop on the pto end and
        > > > directly use the needle thrust bearing on that end, and then
        > decide
        > > > what to do about leaving the flywheel on. With the small prop
        you
        > > > would be using, maybe you could get by with it. I think you
        > should
        > > > plan on a wood prop though, I doubt if you could get anyone to
        > sell
        > > > you an adjustable composite prop for it.
        > > >
        > > > Jerry
        > >
        > > > >To consider this for a tractor prop installation, I would need
        > to know
        > > > >if the engine bearings could handle an outward thrust load,
        > preferably
        > > > >on the flywheel side.
        > >
        >
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