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Thumper---A new 1 3/8" bore i.c. engine

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  • Still feeling crappy, but good enough to go for my "fat mans walk" and watch YouTube videos. There is a 4 part series of videos about "This Old Tony" making a go cart for his son. There is nothing too amazing about the go cart, but my God, the man is a virtuoso with a tig torch. He makes it look so easy to weld up all the different joints. I've built a couple of go carts over my lifetime, but the frames were either stick welded together out of old bed frame angles or oxy-acetylene brazed from electricians conduit.
    Brian Rupnow
    Design engineer
    Barrie, Ontario, Canada

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    • I was thinking about you yesterday Brian. A pipe flange needed to be welded to a pipe. I TIG welded it on my rotary welding positioner. I built the table myself and I have it set up with a foot pedal that allows me to start and stop the table and adjust the speed of rotation on the fly. So I have the TIG foot pedal, the table foot pedal and the welding to keep track of while welding.
      Location: The Black Forest in Germany

      How to become a millionaire: Start out with 10 million and take up machining as a hobby!

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      • And here we have the second flywheel/fan hot off the welders bench. Ignore the stuff to the left of the flywheel---thats just practice welding. I spent an hour this morning playing with the foot-pedal while welding, to get used to changing the size of the arc puddle and not letting everything run away out of control. The flywheel still has to be cleaned up, and "trued" on the lathe but it looks a lot better than the first flywheel did immediately after welding. I am an old dog, but I am learning new tricks.
        Brian Rupnow
        Design engineer
        Barrie, Ontario, Canada

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        • good stuff Brian! The brain is the most important organ in my opinion and it looks like you're giving it plenty of exercise.

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          • Leapin' Lizards Annie--Just look at that thing!!! Both flywheels fit where I intended them to. I could probably spend a day "fettling" around the welds to blend everything in, but I'm not going to. Plan is to knock down any high spots and any sharp points, then paint them. I had purchased a can of John Deere Green, but decided that I didn't like it. Went back and bought a darker green which I think will look nice.
            Brian Rupnow
            Design engineer
            Barrie, Ontario, Canada

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            • Old welders saying -- "A good die grinder makes a good welder"

              Looks like you're having fun anyway and thats what matters
              25 miles north of Buffalo NY, USA

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              • Ladies and Gentlemen-I present "THUMPER" in all it's beauty. Yesterdays paint job dried overnight, and everything got unmasked and assembled this morning. Now I get to the point where "Thumper" can not stay on it's merits as being pretty---It has to actually run for me. I started this build on or about the 1st. of March, and had everything completed by the beginning of April except for the flywheel/fan blades. I had some time in April devoted to purchasing and learning to use a new Tig welder, and a few days of stomach flue. I am happy with the way this engine turned out, and will be even happier if the next stage (getting it to run) goes fairly easy on me.----Brian



                Brian Rupnow
                Design engineer
                Barrie, Ontario, Canada

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                • that's a great looking build

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                  • Looking really good Brian. Now all we need is to have it speak to us !
                    Larry - west coast of Canada

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                    • Now we get to talk about cam timing. As you can see in the drawing, there is about 125 degrees of "cam influence". That gets doubled when you think of what is happening at the crankshaft, because of the 1:2 ratio between the crankshaft gear and the camshaft gear. So---at the crankshaft we have 250 degrees which we have to account for. When the piston travels full stroke from top dead center to bottom dead center, that accounts for 180 degrees. so 250-180=70 degrees. I like to have the intake valve start to open about 20 degrees before the piston reaches top dead center on the exhaust stroke. I can adjust the cam position to make this happen. If we take that 70 degree figure and subtract the 20 degrees from it, then that means that the intake valve will close 50 degrees into the compression stroke.--I can't set that last figure. That last figure is totally dependent on the shape of the cam. I like my exhaust valve to begin opening at 45 degrees before bottom dead center on the power stroke, and I can set that. So, again, if you subtract that 45 degrees from 70 degrees, that means that the exhaust valve stays open until 25 degrees into the intake stroke. I will set the cams up as written in the text, and see what happens. These calculations do not take valve lash into account, but they seem to work for me when the valve lash is set to about 0.010".
                      Last edited by brian Rupnow; 04-28-2020, 03:51 PM.
                      Brian Rupnow
                      Design engineer
                      Barrie, Ontario, Canada

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                      • An old school engine builder told me that you can always set the cam, even without timing marks, by feel.
                        He put crank of #1 cylinder on TDC, then turn cam until both valves feel equally closed, equally on either side of TDC, then drop the cam gear in place.
                        I tried it without looking at the marks, and sure enough, the timing marks showed up as aligned.

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                        • Brian, had to comment on the real nice looking set of rocker arms and adjusters. I am sure you had all the poking you got about the adjusters on that last engine in mind when you designed these.

                          Patiently waiting for the first running attempts.

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                          • Wow that is one good looking engine! I could easily see casting kits.
                            25 miles north of Buffalo NY, USA

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                            • This morning I'm setting valve timing. There is a lot going on in this picture. On the far side of the engine is a cardboard protractor I made up. It has a wood base and a clearance hole thru it for the crankshaft. It has the degree marks that I want to set my valves to printed on it---20 degrees before top dead center and 45 degrees after bottom dead center. There is a temporary metal stand made up for my dial indicator, and the end of the indicator is setting on top of the intake valve rocker arm. I think I have a Canadian two dollar coin in there for a spacer because I couldn't get the dial indicator quite low enough without modifying the temporary stand. For the intake I have found and marked the flywheel at top dead center, then turned the crankshaft backwards until the top dead center mark on the flywheel was lined up with the 20 degree before top dead center mark on the protractor.(grub screws in intake cam and both gears are locked to camshaft and crankshaft. Then I loosen off the grub screws in the crankshaft gear and turn the camshaft gear in the correct direction until I see the dial indicator start to move. I then lock the crankshaft gear grub screws and the intake valve is set. The exhaust valve is more difficult, because the cam and crank gears are locked in position. I set the crankshaft in a position that is 45 degrees before the piston reaches bottom dead center. I loosen of the grub screws in the exhaust cam and set the dial indicator up on the exhaust valve. Then without moving crankshaft or camshaft, I have to reach in thru the "window" and spin the exhaust cam in the correct direction until it contacts the lifter. (This is far easier said than done). then the grubscrews in the exhaust cam are locked up.
                              Brian Rupnow
                              Design engineer
                              Barrie, Ontario, Canada

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                              • Brian - I noticed that you didn't mention anything about the valve clearance or taking that into account. To get an accurate reading of when the valve starts to move you really should have the dial indicator on the valve spring retainer of the valve you are checking. That would eliminate any clearances in the valve train.
                                Larry - west coast of Canada

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