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A new engine for fall---

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  • #46
    Brian, I've never designed or built an engine in my life, so feel free to rubbish the following thoughts!
    Could you put the valves and their associated gears and cams on opposite sides of the cylinder? That way the valve head diameters could probably be bigger, and the head would be symmetrical, which might combine to give better scavenging. It would also keep the exhaust heat away from the inlet and carburettor. And the valve gears would not have to overlap, making access to each perhaps a bit easier.
    And instead of tappets, as I understand the word, could you not just make each valve stem long enough to thread an adjustable cam-follower directly into into the end?

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    • #47
      Just an idea to stimulate minds- take a discus-shaped object, fat in the middle- cut it in half across the diameter. Stand one part upright on top of a piston. The diameter is about equal to the diameter of the piston. This represents the shape of the cavity that you could mill into a cylinder head. Perpendicular to the piston and the crankshaft, drill a hole through the head which would pass through the cavity near the top of it. On one side of the cavity is the intake valve, and on the other the exhaust valve. The hole basically goes from one side of the engine to the other, and you could properly call it a side valve engine. Intake mixture enters and blows around the cavity and circles down across the top of the piston and back up the other side of the cavity. Exhaust would follow a similar pattern. You might extend the cavity shape into the top of the piston for a circular flow path.

      This would definitely impact the compression ratio, so you would squash this shape as much as required to suit. What you'd end up with is a modified hemispherical combustion chamber.
      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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      • #48
        Not there yet, but slowly getting all the parts in---
        Brian Rupnow
        Design engineer
        Barrie, Ontario, Canada

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        • #49
          I think this could work---The cyan blue backplate would be 3/8" steel with 3 steel stub shafts welded into it. It would attach with 6 bolts and two locating dowels (not shown) to the dark green spacer bar, which is itself bolted and dowelled to the aluminum crankcase. The gears and cams might be machined from bronze or cast iron, something with enough lubricity that they can rotate on the fixed shafts without galling. The con rod has sealed needle bearings in both ends, the dark blue half of the split crankshaft has two sealed ball bearings supporting the end where the flywheel goes. The "follower half" of the split crankshaft would run in bronze bushings. The blue bridge which spans across the top of the aluminum crankcase is the tappet guide, and could be aluminum.


          Brian Rupnow
          Design engineer
          Barrie, Ontario, Canada

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          • #50
            I admit never building one of those, but I'd like to see the cams supported on both ends.
            VitŮŽria, Brazil

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            • #51
              David--I am not really a fan of cantilevered shafts either. However, that being said, it is a 3/8" diameter steel shaft and the maximum cantilever to the center of the cams is only 15/16". I doubt that there is going to be any measurable deflection on the shaft.---Brian
              Brian Rupnow
              Design engineer
              Barrie, Ontario, Canada

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              • #52
                Okay!!---I am happy with everything here, and know it will work. The only "grey" area is attaching the valve body to the cylinder and the cylinder to the crankcase.--I haven't spent any time thinking about the flywheel, and I am pretty certain that like the Jaguar/Canadian Cub engine that I just built, this one will need a built in fan for cooling. The exhaust will be simply a screw-in straight pipe, and the carburetor will either be a copy of the Jaguar carb or my version of the George Britnell carb clone.
                Brian Rupnow
                Design engineer
                Barrie, Ontario, Canada

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                • #53
                  Great job so far Brian. I always read your posts because they are so interesting.
                  You must almost have enough engines to start your own museum in Barrie by now.
                  Looking forward to the rest of this project.
                  I have been carefully looking over the Henry Ford Engine in the latest Home Shop Machinist magazine.
                  I may try and build one this winter.
                  Larry - west coast of Canada

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                  • #54
                    What is the purpose of the reversing gear in the valve train?

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                    • #55
                      It"s not a reversing gear. It's what is called a "jockey" gear. For reasons unrelated to the camshafts, the crankshaft has to be a set number of inches away from the top of the cylinder, to allow the piston to move through its full stroke and not have the con rod hit against the bottom inside of the cylinder as the crankshaft rotates. The cam shafts have to be a pre-determined distance from the top of the cylinder to give room for the valve stems, tappets, etcetera. In a perfect world, the gear on the crankshaft could mesh directly with the cam gears. However, it's not a perfect world, so in order to meet the pre-imposed distance relationships, I put a gear the same size as the crankshaft gear directly above the crankshaft gear. Since it has the same number of teeth as the crankshaft gear, it will rotate at the same speed, only in the opposite direction. The jockey gear also meshes with both camshaft gears, which have exactly twice as many teeth, to give the 2;1 reduction required between crankshaft RPM and camshaft RPM.
                      Brian Rupnow
                      Design engineer
                      Barrie, Ontario, Canada

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                      • #56
                        Originally posted by RichR View Post
                        Maybe try something more exciting, like a jet engine.
                        I think that would be a good idea! For those that might want to try it, here is a free download for plans that one can keep in their "library" for future use....

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                        • #57
                          I gave up on the idea of having a steel backplate with welded in stubshafts. Last night I lay in bed thinking, and I had originally intended to solder the cams onto the face of the gears. This is always a somewhat "iffy" proposition, and as I have said all along, I want to be able to adjust the cam timing independent of the gear teeth. I decided I would be able to do that if I added a hub and set screws to one side of the gears and silver soldered the cams to the 3/8" shaft, while leaving the gears free to rotate into whatever position I wanted them to be in relation to the cam position, then lock them to the shaft with the set screws in the gear hub. This means of course, that the shafts must now be able to rotate. So---I changed the steel plate to an aluminum plate, with two 1" long oilite bronze bushings pressed into the thick part of the plate. The blue circles you see are the heads on the ends of the two cam shafts. They need shallow heads on them to keep then from trying to pull out of the bushings as they revolve. The other end of the camshafts which support the gears and the cams is still cantilevered, but it's only a 7/8" cantilever from the edge of the aluminum plate out to the centerline of the cams, so I don't anticipate any bending. The jockey gear is made from bronze and rotates on a 3/8" steel shoulder bolt which screws into the side of the crank case.
                          Brian Rupnow
                          Design engineer
                          Barrie, Ontario, Canada

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                          • #58
                            We have to get a set of my favourite Chrysler product ignition points mounted somewhere, and since we are in the design phase, I might as well mount them on an adjustable plate so I can adjust the ignition timing while the engine is running. That is easy enough to do by extending the end of the outer crankshaft bushing and bumping up the extended diameter to 5/8". I can then clamp the ignition points mounting plate onto the head of the bushing.
                            Brian Rupnow
                            Design engineer
                            Barrie, Ontario, Canada

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                            • #59
                              So the "jockey" gear is used instead of (adjustable) pushrods, I take it. That will work but how will you adjust valve lash mentioned earlier in the thread? My internal linear thinker is telling me pushrods but I've always had pushrod engines

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                              • #60
                                Brian,
                                My two bobs worth is that you delete the jockey gear; that only saps power. Lower the two other gears and move them *inside* the crankcase.
                                Cheers,
                                Norman

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