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Thread: Senft "Poppin" ENGINE

  1. #21
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    Willy--That slide that blocks off the port is on the end of a cam operated lever. It is only 0.002" thick, so theory is that the suction from the piston will pull it into place to fully block the port.
    Brian Rupnow

  2. #22
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    Jun 2011
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    Love the cylinder. Looks like a ray gun from the cover of astounding.

  3. #23
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    Today I made flywheels. I can't even imagine it, but that's a full 8 hours of my time. These flywheels are somewhat unique, because the hubs will be made as separate pieces. Maybe I'll make them tomorrow.
    Brian Rupnow

  4. #24
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    Nov 2008
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    Two words.

    Pretty!!
    Measure twice. Cut once. Weld. Repeat.
    ( Welding solves many problems.)

  5. #25
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    Not a great deal done today, as I had a few hours of "real" work. I did however manage a pair of flywheel hubs and their accompanying nuts. (I cheated on the nuts---took a pair from my tool-chest and thinned them down on the lathe.) I have never seen flywheels made this way before, but it seems to work okay.
    Brian Rupnow

  6. #26
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    Not a criticism, but an observation. Nothing shows up worse on a model engine than wobbling flywheels. When I make flywheels I generally leave a bit extra on the width and the diameter so that I can mount the finished flywheel on the correct size of arbor and give them a final "dressing" on the lathe to ensure that they are not wobbly as they revolve. Making flywheels with separate hubs that are not in any way "keyed" to the flywheel doubles the effort required to have the flywheels run true on the finished engine.
    Brian Rupnow

  7. #27
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    Jun 2007
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    Anderson SC
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    Quote Originally Posted by brian Rupnow View Post
    Not a criticism, but an observation. Nothing shows up worse on a model engine than wobbling flywheels. When I make flywheels I generally leave a bit extra on the width and the diameter so that I can mount the finished flywheel on the correct size of arbor and give them a final "dressing" on the lathe to ensure that they are not wobbly as they revolve. Making flywheels with separate hubs that are not in any way "keyed" to the flywheel doubles the effort required to have the flywheels run true on the finished engine.
    If the flywheels are dimensionally accurate they should run true. What you are correcting for is a off center bore or something similar. Truing them up as described make them "appear" to be runout free but they will no longer be dimensionally accurate and thus be out of balance. For example, say the flywheel is 1/2 inch thick and wobbles, you true it up, its no longer half inch thick all the way around, some sections are thinner and thus not balanced. Kind of the same principle as mounting something off center in a 4 jaw chuck, the turned diameter will run true but its still off center in the jaws and out of balance. Two piece assemblies with a hub will run true if machined well, they do it every day with pulleys and taper lock bushings for example.

    Of course a bent shaft out of alignment crank will cause the same effect.
    Last edited by Sparky_NY; 03-14-2018 at 11:52 PM.

  8. #28
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    It should be balanced if trued up.... at least if it "wobbles" sideways. To stop the wobble you will take material off until both sides run true, and the thing will still be in balance, just thinner.

    If the wheel "runs out" radially, then if it is made with a hollow center, as usually done.... then if you just true the OD it will be out of balance unless you also true up the ID of the hollowed out portions. If you do that, it will be lighter, but it will be in balance.

    Brian knows that stuff, he'll get it right.
    1601

    Keep eye on ball.
    Hashim Khan

  9. #29
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    Quote Originally Posted by J Tiers View Post
    It should be balanced if trued up.... at least if it "wobbles" sideways. To stop the wobble you will take material off until both sides run true, and the thing will still be in balance, just thinner.

    If the wheel "runs out" radially, then if it is made with a hollow center, as usually done.... then if you just true the OD it will be out of balance unless you also true up the ID of the hollowed out portions. If you do that, it will be lighter, but it will be in balance.

    Brian knows that stuff, he'll get it right.
    I was just going by the process as he described it. He made no mention of balance. or truing up the ID after doing the OD, thus why I made the post.

  10. #30
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    I can't swear to this, but my plan to address the flywheel issue is this. I will probably build the cam and cam washer and install them on one of the flywheels, then mix up a batch of J.B. Weld, coat the hubs with it, insert hubs into flywheels put cam and cam washer on one of the flywheels, then run the nuts down tight, and clean up any squeezed out mess. This should make each flywheel assembly a "composite unit". Then after 24 hours I will mount each assembly on a 3/16" arbor, tighten in place with the set-screws in the hubs, then true each flywheel individually. I am not concerned about balance here, just visual "flywheel wobble".
    Brian Rupnow

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