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Thread: Air cooled 2-cycle motorcycle racing cylinder

  1. #1
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    Air cooled 2-cycle motorcycle racing cylinder

    Making a pattern for a new cylinder for my race bike.
    story about the bike here:

    http://www.highwaymanbikes.com/the-h...ge-road-racer/
    http://www.highwaymanbikes.com/desig...acing-chassis/

    The current cylinders break off on the bottom, not to mention take way to many hours to make, from rare Kawasaki F3 cylinders..
    The F3 cylinder comes with the wrong iron liner, port windows in the wrong place, and the way too weak flange that breaks.
    I literally bore out the stock cast-in iron liner, weld up the aluminum to relocate to port windows, make a custom iron liner, re-machine/grind all the ports back in, and fabricate a base plate to fix the wrong deck height.

    I have ideas on how to reinforce the modified F3 cylinders, but making one is so labor intensive, I might as well be spending the time to make a casting pattern for a superior cylinder, with bosses for through-clamping studs that wont break, the correct deck height that wont require a base plate spacer, streamlined transfer port passages (only possible by casting, not machinable) , and no iron-liner but rather a "Nikasil" plated cast aluminum bore.

    And SO IT BEGINS....

    The old cylinder showing where they break off...


    Making Vinyl castings of the old ports for reference of teh shape...


    My favorit thing: CNC cut "Paper Tooling" and an aluminum fixture to aid in forming the new transfer port patterns...


    How I use the paper tooling...



    Roughing out the port shape in clay, just like grade school art class, only the big boy version :-)


    Showing what the new streamline ports will look like compared to the old "turbulent-bend" ports...


    smoothing op on the inner wall...


    Finished transfer port models...



    And molding of the ports in silicone. The silicone mold will be used to generate urethane hard copies that will be used for core-box patterns, and reference shapes in the cylinder-pattern...



    More to come!

  2. #2
    Senior Member 4cylndrfury's Avatar
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    wow!Subscribed!!!!

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    WHOOOOOOAAAAAAAAA! I love it!

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    looks great!

    How are you calculating shrink? It's a tricky shape for shrinkage. If it were a plate with a hole in it, the shrinkage would be across the diameter. And if it were a paper thin simple cylinder the shrinkage would be along the circumference. A thick walled cylinder has a bit of radial shrinkage i.e. the thickness of the wall plus shrinkage along the circumference. With your casting the edges will cool first and with the larger width on the corners I think you may get an out of round casting, not by much and it will likely be different at the top and the bottom because of the transfer ports.

    Just give yourself enough stock to true things up and you may want to add some stock to the transfer ports to allow for uneven shrinkage and for port matching to the case.

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    Senior Member Wolfcreek-Steve's Avatar
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    Threads like this are the reason I signed on here, I'm staying tuned in.
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    I plan to compensate for shrinkage by popping a Viagra before I pour the metal…

    HaHa, well for real, when I did my cylinder head pattern I inflated every cross section by 2% in size (maybe over kill? I haven’t measured the result yet.)
    For this pattern, I am only as far as the transfer passages in the photos, to make them though there has been significant thought into the as-cast cylinder bore diameter and upper and lower deck height. I am trying to avoid as much port work on the cast-cylinders as possible, so the port windows will be cast ~0.7 mm undersized in the vertical dimension, to allow some “finish match” porting on the final cylinder, the excess stock has been directed to the easiest-to-port face of the passage. The actual transfer flow passages will be used as-cast, and are non-compensated in the clay model shown in the photos, if they shrink/warp up to 1-2% it really won’t be a big deal at all, however some compensation will occur by coating the port patterns with a decent layer of high build primer prior to using them to make the core boxes. The Cylinder-bore diameter will be cast 4mm undersized to allow an ample amount of stock to be bored off, and the upper and lower decks will be given +2mm of extra stock as-cast. So no much calculated shrinkage compensation at all so far, but more of a cast over/undersized where appropriate and rely and machining for the critical features. Machining the decks is used to adjust overall port timings, and ports can be matched to each other.

    I do agree though I would expect a complicated mixed-mode shrinkage in this type of casting, rather than it happening perfectly along a given axis, there is not much symmetry or constant cross sectional thickness in these things at all!

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    2% is a bit over what you should be getting. I have always just used my shrink rules but if I did the math right 5/32"/ foot would be 1.3%.

    I wouldn't be to worried about too much build with the primer on the transfer port cores because it will allow you to use core wash on them to get a better cast surface. I use an alcohol based wash and "sand" the dried wash with my fingers to create a smooth surface. with a bit of practice you can almost eliminate the sand cast texture.

    I think you will be just fine with your plan.

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    To make the core boxes for the transfer ports, and the cylinder / exhaust port cores, I was planning on taking a couple solid wood squares, pinning them together for a parting line, then hogging out a cavity a little larger then the port patterns. Suspending the pattern in one half of the cavity (one wood square), filling with urethane, dressing the parting line, adding wax release, assembling the box and pouting the other half with urethane. With the idea being to have about ”-1/2” thick urethane as the mold, with the wood backing. I have seen this done by filling the cavity with bondo and pressing the core pattern into that instead of urethane, but bondo has more shrinkage. I may need three parting lines for the transfer port core boxes.

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    Senior Member nudge's Avatar
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    sounds like a bit of fun.... Thanks for posting!
    If the spelins rong blam the wife!

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  10. #10
    I'm watching this one too...

    IANaTST (I am not a two-stroke tuner), but won't the increase in volume of the transfer ports reduce the crankcase compression? Also, the turbulence may be deliberate to improve scavenging the waste gases and cylinder filling, two-strokes are complicated like that, four-strokes I can get my head around valve timing / overlap / port shapes, but two-strokes? Black art

    Early two-strokes had deflector pistons to direct the transferred mixture towards the cylinder head to help with scavenging, modern flat-top pistons I assume need the transfer ports' flow characteristics to do the same job, how they do it? Pass!

    Dave H. (the other one)

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