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1" Bore x 1" Stroke Vertical i.c. Engine

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  • This morning I remade the fan from 316 stainless. For some reason I found this fan to be difficult to make. It steps outside the bounds of normal machining, and seems to have about a thousand sharp edges that are difficult to get to with anything bigger than an ignition points file. It definitely looks better than the previous fan which I had made from a badly pitted piece of 0.050" metal I had laying around. It tucks in under the exhaust system, which should be enough to keep my fingers out of it.---And before you rush to tell me---I know that the paint isn't going to stay on the o.d. of the flywheel with that o-ring running on it. The plan is to sand all the paint off the outside diameter of the flywheel before I use it.
    Brian Rupnow
    Design engineer
    Barrie, Ontario, Canada

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    • Brian, you always seem to come up with the most elegant solutions, I love the way the fan is mounted and proportioned.

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      • And if you wondered where the electrics are, there they are, tucked in behind the flywheel. When the flywheel is installed, they are hidden in behind it.

        Brian Rupnow
        Design engineer
        Barrie, Ontario, Canada

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        • Nickel--The fan tucks in there nice, doesn't it.---Almost a zero clearance situation, but exactly where it needs to be to cool the top of the cylinder.----Brian
          Brian Rupnow
          Design engineer
          Barrie, Ontario, Canada

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          • The gaskets are all made and installed (except for the one between the crank-case halves). The ignition timing has been set. In this picture I am setting the exhaust valve opening with a printed degree wheel and a pointer attached to the crankshaft. This valve is easy to set. I just loosen off the set screws holding the small gear to the crankshaft, rotate the flywheel until the piston is at the very top of it's stroke (as determined by a a hex wrench down the sparkplug hole resting on top of the piston), this corresponds with the zero degree mark on the degree wheel. Then turn the flywheel until the pointer is pointing at 25 degrees before bottom dead center and lock the crankshaft in position. Then I turn the large gear on the camshaft in the appropriate direction, until the cam just contacts the lifter and starts to move the rocker arm. Then I tighten the set screws in the small gear on the crankshaft in that position. Setting the intake cam position is going to be considerably more difficult, as I have no access to the cam to lock it to the cam shaft. I will have to calculate the degrees of offset between the intake and exhaust valve and remove the camshaft from the engine to set that. For the sake of the picture I have turned the flywheel and crankshaft to a position that shows the pointer.
            Brian Rupnow
            Design engineer
            Barrie, Ontario, Canada

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            • I'm doing some pondering here, and it has to do with the rotational position of the intake cam. Both of my cams are exactly the same shape, and both of my valves are exactly the same shape. Top dead center and bottom dead center of the piston are exactly 180 degrees apart. My exhaust valve is set to begin opening 25 degrees before bottom dead center and to close at about 35 degrees after top dead center.--If I position my cams to be exactly 180 degrees apart, then it stands to reason that my intake valve will begin to open about 25 degrees before top dead center and close at approximately 25 degrees after bottom dead center. I'm not certain how this valve timing will effect the performance of the engine, but it certainly makes it a lot easier for me if I can just position the cams to be 180 degrees to each other.--Does anyone have thoughts on this?---Brian
              Brian Rupnow
              Design engineer
              Barrie, Ontario, Canada

              Comment


              • Here is one lecture on the subject : https://www.youtube.com/watch?v=hfKTh7GkVME

                The presenter's accent is a challenge (for me), but his chart shows the difference between low speed and high speed engines.

                I suppose there could be some alteration of valve timing depending on scale, too, with smaller engines needing different timing than larger engines. It would be nice to hear from some modelers with experience with this.
                Attached Files
                Last edited by aostling; 03-21-2021, 02:39 AM.
                Allan Ostling

                Phoenix, Arizona

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                • Okay, working with the cams I have made, (which have 120 degrees of angular contact ) that means that it affects 240 degrees of crankshaft action. so, I begin to open the intake 15 degrees before top dead center and it closes 45 degrees after bottom dead center. the exhaust begins to open 30 degrees before bottom dead center and closes 30 degrees after top dead center. The angular difference between the cam lobes is approximately 100 degrees when fixed in place on the cam shaft. The following bit of arcane knowledge is something I researched and read about a few years ago when I built my opposed twin i.c. engine.

                  Now let me see if I can get my head around this. The piston is moving from top dead center to bottom dead center on the power stroke, with both valves closed. 30 degrees before bottom dead center, the exhaust cam which is leading begins to open the exhaust valve. Since there is a 1:2 relationship between crankshaft revolution and camshaft revolution, that translates to 15 degrees of camshaft rotation.

                  As the piston reaches bottom dead center and begins to travel up on the exhaust stroke, the exhaust valve stays open during the full upwards travel of the piston which represents 180 degrees of crankshaft rotation, or 90 degrees of camshaft rotation. Then as the piston reaches top dead center on the exhaust stroke, the exhaust valve stays open for 30 degrees of crankshaft rotation (15 degrees of camshaft rotation) during the intake stroke before it fully closes. This adds up to a total of 240 degrees of crankshaft rotation, or 120 degrees of camshaft rotation.

                  So—Let’s back up a little bit to where the piston is coming up to top dead center on the exhaust stroke with the exhaust valve wide open. 15 degrees of crankshaft rotation (7.5 degrees of camshaft rotation) before the piston reaches top dead center, the intake valve begins to open. It stays open thru the full intake stroke of the piston (180 degrees of crankshaft rotation, 90 degrees of camshaft rotation, and then as the piston reaches bottom dead center on the intake stroke and begins to move upward on the compression stroke, the intake valve stays open for an additional 45 degrees of crankshaft rotation, (22.5 degrees of camshaft rotation.)

                  This adds up to a total of 240 degrees of crankshaft rotation, (120 degrees of camshaft revolution).

                  So---we see that the exhaust cam and the intake cam must in this case have the same profile, since they must both be “active” an equal number of degrees of rotation. We also see that there is a total of 45 degrees of overlap at top dead center where both intake and exhaust valves are open at the same time.---this is typical of a “mid-range power/speed” engine. Hi speed/ hi-performance engines can have a greater overlap, while slower running engines must have a smaller overlap.

                  Now, there is a marvelous calculation used to position the intake and exhaust cams rotationally in respect to one and other. I have read this calculation enough times to make my head explode, and will repeat it here:

                  “Take the total of the valve open periods, divide by 2, subtract the total valve overlap and divide the result by 2”

                  So—the total of the valve open periods is 480 degrees of crankshaft rotation, divided by 2= 240 degrees.

                  240 degrees -45 degrees of overlap=195 degrees. Then 195 divided by 2=97.5 degrees of rotational separation between the intake and exhaust cam lobes.

                  This information was gleaned from a number of sources, but primarily from information found in “Model Four Cycle Gasoline Engines” by C.L. Mason and in “Miniature Internal Combustion Engines” by Malcolm stride.

                  I laid this out in 3d cad, independently, and came up with a lobe separation of 97.43 degrees, which confirms the long winded mathematical approach.
                  Brian Rupnow
                  Design engineer
                  Barrie, Ontario, Canada

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                  • I get lost in this cam timing business, and the only thing holding me back from running the engine is setting the cams. I will set it up to run with the last numbers I gave and see what happens. In the best possible case, the engine will run and we'll all be happy. In the worst possible case, the engine won't run, and I'll have to pull it apart to change the cam timing.
                    Brian Rupnow
                    Design engineer
                    Barrie, Ontario, Canada

                    Comment


                    • This is another shot of setting the exhaust cam in the correct position, using a degree wheel and a dial indicator. I kept setting it over and over again "by eye", and each time it ended up in a different rotational position. Finally I resorted to a dial indicator so I could actually see the needle start to move when turning the cam gear by hand. I wanted to get the exhaust cam positioned correctly before pulling things apart to set the intake cam. What I have now seems to be repeatable, so I think it's time to pull the engine apart and set the intake cam, using the exhaust cam as reference.
                      Brian Rupnow
                      Design engineer
                      Barrie, Ontario, Canada

                      Comment


                      • Somehow, I'm not getting any joy from the cams that I made. I can set them to open at the exact time that they are supposed to, but they are staying open too long. The only thing that will account for that is that instead of having 240 degrees of interaction with the crankshaft (120 degrees of camshaft), I am getting much more than that. I have spent most of today measuring and adjusting and I have to stop now and think about what I am going to do.
                        Brian Rupnow
                        Design engineer
                        Barrie, Ontario, Canada

                        Comment


                        • Yowee!!!--Something very, very strange is going on. I just couldn't believe that my cams were far enough out to cause the issues I've been having with valve timing. I have spent three days going over everything I have done while building this engine, and nothing jumps out at me. Then, this morning, I loosened of the set screws in both timing gears, put a mark on a single tooth of each gear, and turned the small gear by hand. Since I'm running an exact 2:1 ratio, the marks on the two gears should line up, then be out of line by exactly 180 degrees, then line up again on the second rotation.---but that's not happening. On every second rotation, the alignment marks are out by one tooth, and gaining on each revolution. How can this be??? So, next thing was to count the number of teeth on each gear. The small gear has 25 teeth just like it's supposed to have. The large gear has 48 teeth, not 50 like it's supposed to have!!! How can this be--The center to center distance on the crankshaft and camshaft are correct for a 25 tooth and a 50 tooth gear. And the two gears mesh okay!!! I've never had this happen before. Next move will be to check my drawings and engineering information and remake the big gear.--What a strange, strange thing.
                          Brian Rupnow
                          Design engineer
                          Barrie, Ontario, Canada

                          Comment


                          • HELP!!!---I'm losing it this afternoon. I have a 90:1 ratio rotary table. I'm using a 20 hole divider plate. My chart says that for a 50 tooth gear I need one full turn of the handle (which gives 4 degrees) and 16/20 of a complete turn. When I made this 48 tooth gear (which was supposed to be 50 tooth) I turned the crank on the rotary table one full turn and 16 open holes. Obviously, that was wrong. Doing some layout work with my cad system, it seems that The 16/20 should have been 15 holes plus one more space to where the crank pin engages with a hole in the divider plate. If I'm right, then that may account for the wrong number of teeth on my gear. Somebody sort me out please---I've looked at this until I'm going cross-eyed.---Brian
                            Brian Rupnow
                            Design engineer
                            Barrie, Ontario, Canada

                            Comment


                            • Originally posted by brian Rupnow View Post
                              HELP!!!---I'm losing it this afternoon. Somebody sort me out please---I've looked at this until I'm going cross-eyed.---Brian
                              Probably time for a nap and a day off. I have done similar things, recently.

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                              • Heck I had to go take a nap just reading about all this! LOL I'll bet you get it sorted out.
                                olf20 / Bob

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