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Re: Straight Question ....

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  • sstationcpl
    A few comments- I think that it chills use of these when the instruction manual specificly states not for aircraft use we saw that on a kohler we bought for
    Message 1 of 76 , May 2, 2005
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      A few comments-
      I think that it chills use of these when the instruction manual
      specificly states "not for aircraft use" we saw that on a kohler we
      bought for a hovercraft. - but I can see the lawsuits now if that
      wasn't in them , better to have an outside corporate shop do that
      fun stuff. but would you pay more for it?
      As for cranks, too much combined belt tension and overhung load
      will break them on a reduction drive. Vibration is a second issue,
      on a geared drive backlash could wipe it out.
      The oiling and connecting rods are the "fun" parts, but the newer
      ones will often go 1600 to 3000 hours on golf course greens mowers, -
      full throttle.
      There are a few nice little 12-16 hp subaru golf cart engines out
      there that could be fun , esp with a blower..
      I think the weight is worth getting out of 2 stroke hell.
      A lighter alloy flywheel to hold the magnets would be an answer,
      the smaller brigs engines have used the mower blade for a flywheel
      for decades - those engines have to have the heavier horizontal
      flywheel swapped on to run without the blade at less than 3000.
      usually the parts for a v-twin are the same as a the single x2
      simpler to manufacture, and size is a huge issue.
      As for how light, How far are you willing to go? the biggest
      weight is the crank, but even that could be polished down an bit.
      A well massaged engine with a few goodies - carbs, rods, cam
      grind, spark advance, some port work, good exhause pipe. - could
      probably keep right up with the 2 strokes pound for pound. A 2
      stroke crank is not cheap or light.
      Gotta remember that these are built to sell dirt cheap to sears
      to put on grannys lawn mower or uncle Ralphs cement mixer.








      --- In Small4-strokeEngines@yahoogroups.com, JERRY <jerbook@m...>
      wrote:

      > >Don't agree that lack of support from manufacturers is holding
      back
      > >the development of these engines. ................
      ...............
      > >* Are there any horizontally opposed engines or are they all Vee
      > >Twins ?..............
      > >> >
      > >* Are there any known crankshaft or other catastrophic failures
      of
      > >these engines with propellers fitted ?
      > >
      > >* Typically how much can these engines be lighened by stripping
      them ?
      > >
      > >
      > >Steve
      > >
      >
      > Briggs has a 31 hp readily available, and it looks interesting. The
      > following link might still list them, along with many others.
      >
      > www.smallenginewarehouse.com
      >
      > My 25 hp Kohler weighs about 82 pounds stripped of the starter,
      blower,
      > shrouds, muffler, etc. It weighs about 65 pounds without the
      flywheel, but
      > needs some alternate ignition system that way. The Rotax 277 with
      gear box
      > weighs about 70 pounds.
      >
      > As far as crank problems go, at least on the Kohler 25, don't ever
      put the
      > propeller on the pto end of the crank and leave the flywheel on
      the other.
      > The crank WILL break after a few hours from torsional vibration.
      Mounting
      > the prop, with an adapter, to the flywheel does work and has gone
      for
      > hundreds of hours on air boats.
      >
      > There is one case where a crank broke while using a belted
      reduction drive
      > from the pto end. But no one knows for sure why it broke.
      >
      > As far as the v-twin configuration is concerned, I think it is more
      > compact, lighter and easier to cool that way. Both rods run on the
      same
      > crank throw, but with the v configuration they both don't move the
      same
      > direction as they would with an opposed configuration running on
      the same
      > throw, so less vibration. An opposed engine running on 2 throws,
      180
      > degrees apart, would need to be a larger, heavier engine.
      >
      > Regards,
      > Jerry Booker
    • 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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