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Thread: Air cooled 2-cycle motorcycle racing cylinder

  1. #21
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    looks good, nice 3d puzzle your making there. Looks like a four piece mold with two loose pieces, one for the very bottom of where the transfer port joins the cylinder for the piston skirt, and one for the other end of the port. Its always preferable to have cores like this open from each end but in this instance I think that would result in some thin and fragile core box pieces. I would make a box with steeply tapered sides to hold all the individual parts. Done right you wouldn't need to use any screws or dowels to hold the parts together. turn the box over and rap it and all the parts come out then you can pull each part off the core.

    Are those registration button molds you have sitting near by for the extra plastic?

    - - - Updated - - -

    I spoke too soon, It didn't look like you had the draft for a three piece mold. Your getting good with the bondo.

  2. #22
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    thanks! yep those are registration button molds that i use for the excess plastic. I am accumulating a lot of the buttons, they are designed to for the buttons in sand.
    I like the idea of the tapered core-box with drop out look parts.

    below are photos of my finished port core boxes...







  3. #23
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    More progress, beyond core boxes an onto the pattern...



    One last core box for the cylinder core, and shellac coating...


    The actual core boxes were used to make urethane castings of the core structures that will be used as parts of the pattern, note two or the ports are split at what will be the parting line and were cast as two pieces.


    These are all the parts that will make the core structure, however two port-cores here were produced as two pieces to use in the pattern as they will bl split at the parting line.





    And here is a full model of the core structure with core-prints, as a split pattern. The rest of the pattern will be built on top of these models.

  4. #24
    Senior Member nudge's Avatar
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    Very cool! I will have to keep a good eye on this thread...... I may just require it later.
    If the spelins rong blam the wife!

    How to build a Nudge burner (oil)

  5. #25
    Awesome work, That sander is sweet! is it a Wilton?

  6. #26
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    Very impressive core work. I just read your Website postings on your bike deveopment. Wow. Impressive work with a welder, with the grinder, with the lathe. Great skills.

    Regards.
    Mark

  7. #27
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    A very informative thread and great work. Well deserving of a sticky
    A calm sea does not make a skilled sailor....

  8. #28
    Impressive work.
    I found that trying to find what I need and then make it work with what I have, is more trouble than designing what I want and doing it.
    me

    "Quick decisions are unsafe decisions."
    Sophocles

  9. #29
    6.jpgHello Sir....

    I'm Sven from Germany. I also built a racing cylinder, but with less success like you.
    Currently i have some problems with the oilsand. I cant cast the outer shape, the cooling fins are sooo....grrrr...

    best regards
    Sven

    5.jpg3.jpg4.jpg2.jpg1.jpg
    Last edited by Stud54; 01-18-2016 at 02:10 PM.

  10. #30
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    nice looking patterns and cores !

    I will probably be going to some kind of 3D printing in the future.
    I have tried some low budget 3D printing to make finned cylinder halves just like yours but they were way to rough to pull out of the sand. yours look much smoother then the ones I had made. I have had smaller patterns of less complicated things poly jet printed but the cost is too high for something the size of a cylinder.

    looks like a small displacement reed valve you are making, I like the three port exhaust!
    The racing class I am building this cylinder for restricts me to 1968 3-port transfer layout with a single exhaust port.

    I have been successful making a wooden pattern for a large (for a motorcycle) air cooled head, you can see the sand molds on page two of this thread with a link to a post about that project (below)...

    I switched to using either Chem Bond or Phenol Urethane bound sand, pay attention to the sands hardness and pull the pattern when the sand is still a bit green and not full hard (read up on this in my cylinder head thread, link below). Using test patterns of finned structures I stuck several in the molds and ruined them before learning what it takes to mold a deep finned structure. You must make sure all your fins have real draft. With only 1-1.5 degrees of draft across several inches of height on that many fins it is easy to screw up the draft and get it stuck. also make sure the pattern is dead smooth. With hand made patterns I sand, sand, sand, sand, and sand again, using high build primer to help smooth between sanding, and a smooth lacquer to finish. With as much low-draft surface area as cooling fins have, you would be surprised at how few imperfections it takes to get the pattern stuck or ruin the sand mold. Also use a good release agent on the pattern designed for the type of sand binder that you are using.

    I will be posting more photos of this project soon!

    molding a deep finned cylinder head:
    http://www.alloyavenue.com/vb/showth...ns-to-castings

    chemically bound sand hardness and strip times
    http://www.alloyavenue.com/vb/showth...and-green-sand

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