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A new engine for fall---

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  • I've heard it said that "Close only counts in horse-shoes and hand grenades." There is one other place that it counts, and that is clearance where the con rod exits a round hole in the bottom of the cylinder. I showed lots of clearance in my 3D cad model when I took a section view thru the center of the engine, but in the case of a rectangular cross section rod exiting thru a round hole in the bottom of the cylinder, it doesn't tell the whole story. If you look at the edge of the con rod, about at the center, you will see how much clearance I DIDN'T have. I thought I felt some resistance when I first rotated the assembled engine by hand, but it was stiff and I was able to get a full rotation after working the crankshaft back and forth a bit rotationaly. I will file a radius on the corners of the con rod, and that will take care of things. There is no moral to this story, other than the fact that building one of these small engines always has a few surprises in the process. Laying in the picture with the con rod and piston is the newly machined and hardened wrist pin.
    Last edited by brian Rupnow; 10-13-2014, 10:20 AM.
    Brian Rupnow
    Design engineer
    Barrie, Ontario, Canada

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    • I am down to the point in my parts making where all that is left is the carburetor, exhaust pipe, and the cooling fan system. I still have a lot of bronze laying around, so decided to make this part today, just because it's do different. Alas, it is not going to happen. Whatever it is about bronze, if the bandsaw blade has any wear on it at all, it simply won't cut bronze. A new blade, it cuts fine. A slightly used blade, and it just isn't going to happen. The blade still cuts aluminum and steel with no problem but not the bronze. My metal supplier who has a big industrial size self feeding bandsaw and cuts the slices of the 5 or 6" diameter " bronze billet" I have says the same thing about his saw. I would switch to aluminum for the part, but I have to be able to silver solder the fan shroud to it.---Darn!!!
      Brian Rupnow
      Design engineer
      Barrie, Ontario, Canada

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      • Brian is there anybody in town with a water jet? I bet that if you went and chatted them up, while bringing along a couple of your projects to demonstrate, they would run that profile off in ten minutes AND give you coffee!
        Duffy, Gatineau, Quebec

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        • Duffy--Nobody that I know of. I bought a piece of brass today big enough to make the part for $12.---Brian
          Brian Rupnow
          Design engineer
          Barrie, Ontario, Canada

          Comment


          • Now here is something a little different. I really didn't like the look of the exhaust pipe running out of the engine on an angle, and the carb being mounted on an angle, but I had to design it that way so the exhaust wouldn't interfere with the carburetor. Today I was down at Partsource, an automotive supply store, and seen a rack of steel 90 degree and 180 degree bend steel tubes for automatic transmission repairs. For a couple of bucks, I thought "Hey---If that worked out, I could run the exhaust straight out from the engine and mount the carburetor at 90 degrees." I can't bend anything on that sharp a radius without kinking it badly. That tube measures 3/8" o.d. and has a .028" thick wall. I will keep you posted on this and let you know if it works out.---Brian
            Brian Rupnow
            Design engineer
            Barrie, Ontario, Canada

            Comment


            • For reasons far more complex than I want to go into (but mainly involving how little material was left beside the counterbored bolt holes), I have went to a total redesign of this part. I don't do this terribly often, but since it is almost the last major part, and because it will be made of brass now instead of bronze, I have redesigned it. I finished the last of my "drop in" engineering design contracts this morning, so hope to complete this part and possibly the fan tomorrow.
              Brian Rupnow
              Design engineer
              Barrie, Ontario, Canada

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              • If the engine runs, I can guarantee that it will run cool. The white plastic fan is out of some computer hardware. I am not crazy about the color of it, (I may paint it) but at least the pitch on the blades is correct. I realize that the curvature of the blades would make it more efficient if it was going to turn counterclockwise, but it still puts out a good column of air if turned clockwise (I set all my engines up to turn clockwise.) That is because I use my variable speed drill as a starter, and if I run it counterclockwise the chuck loosens off. I still have to find some thin wall tubing of the correct diameter to solder onto my fan support to act as a fan shroud as per the 3D cad model seen at the early stages of this thread.--those little fans will really chop up fingers.

                Brian Rupnow
                Design engineer
                Barrie, Ontario, Canada

                Comment


                • I think I may try my Chuck Fellows carburetor on this engine. It works great on the Webster. I will make a more complicated larger carburetor if I have to, but I already have the Chuck Fellows carb, and if I use it I can come straight out of the engine ports with both exhaust and carb and not have any interference.--Speaking of exhaust---I kind of like this. You can do nifty things with a piece of 1/2" diameter brass and a 1/16" slitting saw!!!---
                  Brian Rupnow
                  Design engineer
                  Barrie, Ontario, Canada

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                  • Wow Brian. Glasspacks for a model engine!
                    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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                    • Cross your fingers for me guys. It's pretty well all over but the final assembly. I am pleased with the way my intake and exhaust manifold turned out, and my Chuck Fellows carburetor looks real proud setting up there. Yes, I will be bevelling the corners on the tappet guide, gear backplate and fan support just like the solid model, but I thought I would wait until I had everything assembled and do it "in place". All I have left to fabricate is the fan shroud, and I MIGHT do that before I try to start the engine---but I am just as anxious to see this thing run as you are!!!---


                      Brian Rupnow
                      Design engineer
                      Barrie, Ontario, Canada

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                      • Looking very sharp Brian!
                        Cant wait to hear it come to life!
                        Cheers,
                        Jon

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                        • Amazing work! I am excited to hear it!
                          Andy

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                          • What a great looking engine! Congrats on some fine workmanship!
                            Kansas City area

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                            • As I began my final assembly of the engine, a thought occurred to me. The displacement of this engine is quite large in relation to the volume inside the crankcase. I am breaking new ground here (for me anyways) and I thought it MIGHT need a crankcase vent. It might not, too, but now is the time to put one in, while I can still pull the engine all apart and flush it out before I put the rod and piston back in. If I don't need one, that's fine, it won't do any harm and didn't cost any money. If it does need one, at least it's in there.----Brian
                              Brian Rupnow
                              Design engineer
                              Barrie, Ontario, Canada

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                              • After a full day of final assembly, individual cam timing, ignition timing, adding a new set of points and condenser, adjusting valve lash, and making a starter spud to fit this particular engine, I am just about ready to Rock and Roll. Has it got compression?--Hard to tell. It's a brand new engine, and it's too stiff to tell if I have compression or not when turning it over by hand. Tomorrow should tell me more---
                                Brian Rupnow
                                Design engineer
                                Barrie, Ontario, Canada

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