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Building the Trevithick Engine

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  • Keyways have been added to the flywheel, bronze gear, and to the crankshaft. It helps, but still doesn't let the engine get "over the hump" at each end of the stroke and continue running. Once an engine like this runs, it quickly wears down any "tight spots" and the longer you run it, the smoother it gets. Of course, the magic is in getting it to a point where it will run under it's own power. There really aren't any more changes I can do mechanically to get it running. This leaves me with two options. Make a bigger, heavier temporary flywheel to get it running, or hook it up to an electric motor and let it run for a couple of hours to get rid of any remaining tight spots. The electric motor method is the cheapest, since I don't have to buy any material, but this is not an easy beast to hook an electric motor to. I am going to call my metal supplier and ask about the price of a 8 1/2" square plate x 1/2" thick to make a much heavier flywheel.
    Brian Rupnow
    Design engineer
    Barrie, Ontario, Canada

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    • I guess a single cylinder engine, especially if it is a bit stiff, can get stuck at the top or bottom of the stroke. All it has is the weight of the rotating flywheel and as you say, the precise timing of the valve change over to start it on the next stroke.
      Larry - west coast of Canada

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      • Actually, what's causing the problem is the 4 way valve setting on top of the cylinder. The engine will coast quite happily around the end of stroke positions. The 4 way valve is causing enough drag when it is engaged that it brings the movement to a stop. Hopefully, a heavier flywheel will get thru that bit of hard spot until the 4 way valve wears in a bit and doesn't put so much drag into the system. The way this beast works is that the slider begins to move the valve part way thru it's stroke, and just as the piston reaches the end of it's stroke, the valve is fully engaged. The flywheel gets the engine over the end of travel dead spot, and since the valve has been shifted, he piston heads in the other direction. Repeats the same way at the other end of stroke.
        Last edited by brian Rupnow; 10-15-2020, 03:14 PM.
        Brian Rupnow
        Design engineer
        Barrie, Ontario, Canada

        Comment


        • Can you remove or disconnect the 4-way valve and run it in by itself?

          Can you cobble together a rubber/friction connection to drive the flywheel by its OD with an electric motor? It’s only got to work for a couple of hours and has to be easier than machining another 10-lb flywheel.
          Last edited by DrMike; 10-15-2020, 03:52 PM.

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          • Now you know how I spent my afternoon. This started life as a piece of 1/2" x 8 1/4" x 10" hot-rolled flatbar. There is no center hole in it yet, just a good center-punch mark. It has double sided tape on the side facing the lathe jaws and is held in place by a live-center in my tailstock. I cut the 4 corners off with my bandsaw and then spent the afternoon nibbling away at it until it is perfectly round. This method always works well for me, but you can only take about 0.010" depth of cut or the tape slips. I'm not going to put a lot more time in this flywheel. Tomorrow it will get a centerhole and keyway and set screw, and have a #10-24 thread put in 1 1/2" off center for the shoulder bolt which connects the con rod. If the heavier flywheel does the job and makes the engine run, I'll worry about doing some cosmetic work on it later.
            Brian Rupnow
            Design engineer
            Barrie, Ontario, Canada

            Comment


            • Originally posted by brian Rupnow View Post
              . . . If the heavier flywheel does the job and makes the engine run, I'll worry about doing some cosmetic work on it later.
              If the heavier flywheel doesn't make this version of the engine run, you could restore the original valve/cylinder mechanism. Maybe that's all it needed!

              Allan Ostling

              Phoenix, Arizona

              Comment


              • It is currently running the original valve and cylinder configuration. This is the way Trevithick's engine was built.
                Brian Rupnow
                Design engineer
                Barrie, Ontario, Canada

                Comment


                • Brian- adding a larger flywheel might help.
                  (should)
                  Something that you might be over looking is that when the entire vehicle is connected and on the tracks, the engine’s mass contributes to the “flywheel effect”
                  When starting, the engine might have had to have been barred off dead center or pushed off center to get going.
                  To be sure, this was very early technology so, comparing this to even the Rocket with it’s twin cylinder design and not having any dead spot, is just not the same.
                  You might have to get some tracks to try it out.
                  Or, a big ass flywheel!

                  Sid

                  Comment


                  • -Big changes with the heavier flywheel. The flywheel is rocking back and forth like crazy between top dead center and bottom dead center under air pressure. This is very promising. Based on what it's doing now, it should just require some adjusting of the valve actuators on the slide bar. I have just blown an internal hose and have to tear things down to reconnect it. Is there any kind of liquid glue that I can permanently glue the neoprene hoses to the brass or steel tubes on the 4 way valve ? I do have some small spring wire clips from the hobby shop, but at higher air pressure the hoses keep blowing off. Crazy glue sets up so quickly that I wouldn't have a chance to put some glue on the steel tubes and then slip the neoprene hoses over them. Is there something like a "delayed action" super-glue? Sid--I have the big gear off for now until I get the engine to run, so the mass of the engine doesn't really have any effect at this stage.
                    Last edited by brian Rupnow; 10-16-2020, 11:53 AM.
                    Brian Rupnow
                    Design engineer
                    Barrie, Ontario, Canada

                    Comment


                    • Brian- agreed with the gear not engaged with the rest of the assy. I’d it were, and this could roll down the tracks, you would benefit from that inertia.

                      Comment


                      • Brian if you have a marine supply shop around there look for Sikaflex 291 or 3M 4200. Either one will bond the hose to the fitting and you would probably have to cut the hose to get if off. I used to use the Sikaflex on cooling system hoses on engines. Some of the castings where so rough that it was hard to make it seal with just a hose clamp. Put the Sikaflex on and you probably would not be able to get it off again without splitting the hose with a knife.
                        Also I would not use the spring clamps because the pressure is probably springing them open. Try and get some real small hose clamps that fit your hose.
                        Last edited by Cuttings; 10-16-2020, 01:05 PM.
                        Larry - west coast of Canada

                        Comment


                        • Just how high did you have the air pressure cranked up trying to get it to run?

                          Comment


                          • I learned three new things today. #1--There is a type of crazy glue that doesn't dry instantly--it gives you about 15 seconds between when it is applied and when it dries. This is enough time to coat a hose barb (actually a piece of 0.185" diameter brass tube) and slip a neoprene hose over it before it becomes absolutely immoveable.---If you're quick!!
                            ---#2--If you have a bunch of air connections inside something else that requires an hours work to take it apart, then never, ever, ever use neoprene tubing pushed onto metal tubes for connections.--Make them from metal tubing and solder them in place.
                            ---#3---Engines which have wheels on them are as suicide prone as lemmings, which jump off cliffs into the sea. I've probably grabbed this damn thing out of the air half a dozen times today when it jumped off my desk. I haven't moved so fast since my wedding night.
                            Brian Rupnow
                            Design engineer
                            Barrie, Ontario, Canada

                            Comment


                            • Careful how you grab that thing ! Every time I look at it I think of all the pinch points there are. A finger in the wrong spot would NOT be good !

                              Comment


                              • Along with different set times for super glues, they also come in different viscosities. Another product used with the glues is "accelerator", a spritz on hard to bond surfaces increases the adhesion a lot, the accelerator can also be sprayed on a joint with the slow set glue to instantly set it off. There are also super glues special for rubber products. There is a product called "micro balloons" that is used with the glue to make fillets and fill larger gaps. Once again, the RC airplane boys use these products constantly and a RC hobby shop would have a wide selection.

                                Here is just one sample of one brands variety available http://www.hobbylinc.com/hobbylinc-i...xoCgo8QAvD_BwE

                                Here is several pages from the same hobby supply showing different brands etc http://www.hobbylinc.com/cgi-bin/s8.cgi?cat_s=RGC&p=2

                                And lastly, here is a sample of the various kinds of ball joints, rod ends etc that would be very useful in miniature engines http://www.hobbylinc.com/rc-airplane-pushrod-connectors
                                Last edited by Sparky_NY; 10-16-2020, 08:42 PM.

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