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Senft "Poppin" ENGINE

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  • #76
    Just a quick and dirty scrawl this morning to see what things would look like with a base and a burner.
    Brian Rupnow
    Design engineer
    Barrie, Ontario, Canada

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    • #77
      Brian, the major diameter for a 0-80 thread is 0.060". If the rod is a full 1/16", that's 2 1/2 thou more. I haven't cut threads that size, but I would think that's a whopping oversize for that small a thread, especially since it's common practice to die-cut threads on stock that's a bit under the basic major diameter. Wouldn't hurt, I think, to reduce that 1/16 to a thou or three under 0.060".

      I'm sure you know as well as I do, when spreading dies, they don't give any warning before snapping.

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      • #78
        Where do I get a piece of 0.020" diameter spring wire? I'm thinking guitar string---maybe?
        Brian Rupnow
        Design engineer
        Barrie, Ontario, Canada

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        • #79
          Brian,
          Try your local hobby shop. I have found some carry piano wire (spring steel) for hobby modelling.
          Glenn Bird

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          • #80
            Brian
            Too bad you aren't in the US. Amazon has a roll for less than $10 with one day shipping to me.
            "Music Wire" is usually full hard. Would that work?
            Bill
            I cut it off twice and it's still too short!

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            • #81
              have a few mandolin strings here, .014, .022, .024. Just what I happen to have.

              Guitar, mandolin, banjo, viola, violin, should be easy to find something pretty close to .020.

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              • #82
                I worked in my office across town today, and managed to score a piece of .002" shim stock for the valve and a piece of 0.026" spring wire that should get the job done.
                Brian Rupnow
                Design engineer
                Barrie, Ontario, Canada

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                • #83
                  There is definitely a degree of "Hinky" to the valve mechanism on this engine. I have hidden one flywheel here to show the "hinkiness" a little better. The angular relationship between the lever with the roller on it and the small 1/16" diameter rod holding the 0.002" thick valve is adjustable. When the roller is fully "on the cam", the 1/16" diameter rod should be positioned so that the .002' thick valve just covers the hole in the cylinder head and overlaps the edge by about 0.015".--It doesn't in this picture--That was just me placing the 1/16" rod in a perfectly horizontal position when the roller was up on the cam. As you can see, the valve doesn't come close to covering the hole. I can sort out what the angle SHOULD be tomorrow. Then after establishing the correct angle, I have to establish exactly WHEN this event should take place in the cycle of the piston moving in the cylinder. Dr. Senft states that ideally, "Choose a direction of rotation and initially position the cam/flywheel on the crankshaft so that the valve closes the port when the piston has completed about 85% of it's outward motion, that is about 45 degrees before outer dead center."-I've never had so much fun with my clothes on!!
                  Brian Rupnow
                  Design engineer
                  Barrie, Ontario, Canada

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                  • #84
                    I arose from my warm and comfy bed this morning and decided that this would be the day to build a proper engine base and start on a burner. Everything worked, everything fit, and now I'm off to a nearby coffee shop for some lunch. Goodwife has taken #2 son to #1 daughters house in Orangeville to repair a garage door, and I am left to amuse myself for the day. After lunch I will decide whether to finish the burner or set it aside and see if I can start the engine on a "borrowed burner" from another project.
                    Brian Rupnow
                    Design engineer
                    Barrie, Ontario, Canada

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                    • #85
                      With no nuts on the cross shaft, I had to resort to a little "engineuity" to make a hub that will hold the piece of spring wire to spring-load the cross-shaft to close the valve. I just finished this part, and it's true--the smaller the part is, the more difficult it is to make.--I would have never made it as a watchmaker!!!
                      Brian Rupnow
                      Design engineer
                      Barrie, Ontario, Canada

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                      • #86
                        Enough for today. I have the .002" thick valve installed and have set the angular relationship between the valve roller arm and the 1/16" diameter rod that controls the valve. I have "timed" the engine correctly (I think). Senft says to choose a direction of rotation and set the timing so that the valve closes at about 45 degrees before the piston is at "outer dead center".--That confuses me. I have always worked in terms of "bottom dead center" and "top dead center". if anybody would like to clear that up for me, please do. The engine quacks like a duck if I spin the flywheel quickly by hand, so I think that is a good sign. It means that the vacuum in the cylinder as the piston moves towards bottom dead center is pulling the .002" thick valve totally closed.
                        Brian Rupnow
                        Design engineer
                        Barrie, Ontario, Canada

                        Comment


                        • #87
                          Originally posted by brian Rupnow View Post
                          ...... The engine quacks like a duck if I spin the flywheel quickly by hand, so I think that is a good sign. It means that the vacuum in the cylinder as the piston moves towards bottom dead center is pulling the .002" thick valve totally closed.
                          Isn't it supposed to suck in the flame? Sounds like the Prof may have told you to have it close too early???
                          CNC machines only go through the motions

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                          • #88
                            This morning I made a top for the alcohol burner but haven't soldered it on yet. I ordered a set of six 1/8" diameter wicks from Amazon, and I don't want to make the spout that holds the wick until I have the wicks in hand. I've also been looking at what happens with the engine timed the way I have it. When the cylinder is sticking out to the left, I want the flywheels to rotate clockwise. (This keeps from having to run my hand thru the flame after I've flicked the flywheel.) So--piston is at top dead center and valve is wide open. I start rotating the flywheel clockwise. Thru the first 45 degrees of rotation the valve stays open, sucking in flame. During the second 45 degrees of rotation the valve begins to close but hasn't fully closed yet. Thru the third 45 degrees of rotation the valve closes completely. During the last 45 degrees of rotation the valve remains closed and the piston reaches bottom dead center. In the next 45 degrees of rotation as the piston begins to be sucked back up towards top dead center, the valve stays closed for about the first 22.5 degrees, then begins to spring open and by the time it reaches 45 degrees the valve is fully open. The valve then remains open right on thru the top dead center piston position and doesn't close again until the whole cycle repeats itself.
                            Brian Rupnow
                            Design engineer
                            Barrie, Ontario, Canada

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                            • #89
                              OK.

                              I was thinking that if it is 0.002" thick, it will probably be sucked onto the port earlier than expected, I have shim material like that, and it is pretty floppy. hard to be sure when anything happens if trying to control what thin shim material does.

                              Apparently the Prof got it to work.
                              CNC machines only go through the motions

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                              • #90
                                I couldn't wait any longer. I had to see if this thing was going to work or not. I have the base cobbled together with a spacer between the base and the engine in order to get it high enough to use the burner from one of my other engines. I kept trying different timing settings until I worked all around the clock and came back to my original setting. I had to tweak the .002" valve a couple of times to ensure that it actually closed the hole in the cylinder head completely, and away it ran. I am feeling Oh so Good about this.
                                https://www.youtube.com/watch?v=Rhrb...ature=youtu.be
                                Brian Rupnow
                                Design engineer
                                Barrie, Ontario, Canada

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