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A Webster Moment---

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  • A Webster Moment---

    This past weekend I decided to fire up my fat flywheeled Webster that I built a few years ago. I tried EVERYTHING that I know how to do to get it started (And thats quite a fair bit), but there was no way it would run. I checked the coil---I checked the points---I checked the battery---I checked the sparkplug---I twiddled (Yes, a highly technical term) the carburetor seven ways from Sunday. Finally I gave up, figuring that the model engine Gods hated me. That was the only reason I could come up with. Tonight I reluctantly took another look at it. Hey---Son of a gun---When I stopped cranking it with my electric drill, the crankshaft stopped.---But the flywheel kept on going. Somehow, that .093" dowel pin that holds the flywheel in place has sheared in two places--and the timing gear is attached to the side of the flywheel. The probability of getting everything lined up to the point where I can drive that dowel pin thru and out is slim to none. I think that engine will go back up on the shelf for the foreseeable future, or until I have an epiphany about how to get the dowel pin out.

    Brian Rupnow
    Design engineer
    Barrie, Ontario, Canada

  • #2
    Hmmmmm, bet someone can come up with an idea, just give us a bit to ponder this problem.

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    • #3
      can you get to that pin at all? Maybe drill and tap the ends (2-56) and a little slide hammer action will worry the broken bits out. Or maybe that shelf idea, I dunno...
      Last edited by gizmo2; 04-30-2013, 10:03 PM. Reason: add to it
      I'm here hoping to advancify my smartitude.

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      • #4
        It's my guess that you have the cad drawings that you used to create the flywheel. That should help you locate the pin so you could drill and access hole.


        But my first thought was that you could get the timing lined up and then drill a new hole for a new pin.


        Dan
        At the end of the project, there is a profound difference between spare parts and left over parts.

        Location: SF East Bay.

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        • #5
          If the pin sheared off flush with the shaft maybe you could disassemble the crankshaft and press the shaft out of the flywheel. That would give access to the pin in the shaft and maybe the pieces in the flywheel. Also, it appears the flywheel may be made in 2 parts, judging by the bolts in the side. If the pin is on the split line you could get to it that way. It's kind of hard (for me) to tell just from the picture exactly what the assembly is like.
          Kansas City area

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          • #6
            Is there a lesson there about shear strength of pins vs. inertia of fly-wheels for
            the mathematicians to chew over????
            ...lew...

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            • #7
              Lesson one, you need a bigger pin. Lesson two, forget pins, you should have used a key.
              James Kilroy

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              • #8
                The fat flywheeled Webster rides again!!! I got VERY lucky. The pin I had used the first time around was a split pin with a hole down the center. I had a package of sewing needles left over from my carburetor needle valve making adventure, and one of the needles was small enough to fit through the center hole of the split pin. I pushed the pin in lightly from one side of the flywheel until it bottomed out against the crankshaft, then turned the crankshaft slowly until the pin slipped into the broken section of split pin. Once I had everything aligned, some very careful tapping with a very small drift punch removed the 3 broken pieces of split pin. I had a 50% chance of it being in the correct rotational alignment, so I tapped in a new split pin. I then checked the valve and spark timing by rotating the flywheel (which has the small timing gear attached to the side of it) until I decided I had got it right the first try. Took it out to the bench in the big garage, hooked up the gas line and coil wire, gave it a spin, and away it went!!! that carb is a Traxxas #4033 and seems to be the perfect size for engines of this relative bore and stroke size.---They cost about $40.00----Brian
                Brian Rupnow
                Design engineer
                Barrie, Ontario, Canada

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                • #9
                  For what its worth---I just hooked the Webster up to the sawmill and sawed a spruce board with it. By the end of the cut, the Webster was starting to get pretty hot. Those cooling fins are more about show than go. That's what I like about my hit and miss engines with the coolant reservoir. They run much, much cooler than an air cooled engine---and thanks to the hit and miss feature, they pump a lot of cooling air thru the cylinder during the "miss' cycle to carry off even more heat.
                  Brian Rupnow
                  Design engineer
                  Barrie, Ontario, Canada

                  Comment


                  • #10
                    So surely you are now working on rev. 2 of the flywheel attachment scheme to prevent future catastrophe??



                    Dave

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                    • #11
                      No, I am not. That engine was built from free plans posted on the internet, and the .093" dia. roll pin is what was called for in the plans.---And with the standard size flywheel is quite adequate. If I choose to put a much heavier flywheel on it, and shear the roll pin, then "bad on me"!!! Its fixed now, and it runs. If I had designed the original engine, I MIGHT have used a key instead of the roll pin, but the way the build instructions are written it would have been very difficult to know what location to put the keyway in. That entire engine was built and assembled, the timing gears and valve lifting cam and crankshaft positioned at a specific angular rotation, and then the hole for the rollpin was drilled thru the flywheel and crankshaft "in situ". Hundreds, if not thousands of people around the world have built this engine exactly as the plans call for, and probably I'm the only guy that ever sheared that pin off.
                      Brian Rupnow
                      Design engineer
                      Barrie, Ontario, Canada

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                      • #12
                        Can you put a second pulley on that shaft? If so, mount a small fan blade to blow on the engine. Air cooled engines are best when installed on a moving machine or with forced air cooling. I have used motorcycle engines (550cc) to power stationary works and found that it doesn't take much, but does take forced air to keep temperatures in check.

                        Pops

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                        • #13
                          Originally posted by armedandsafe View Post
                          Can you put a second pulley on that shaft? If so, mount a small fan blade to blow on the engine. Air cooled engines are best when installed on a moving machine or with forced air cooling. I have used motorcycle engines (550cc) to power stationary works and found that it doesn't take much, but does take forced air to keep temperatures in check.

                          Pops
                          Agreed, forced air cooling even at low air speeds provides many times the cooling of still air.
                          Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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                          • #14
                            If I actually decided to use that engine as a workhorse, I would put a fan on it. However, its really just a "demonstration" engine, my first i.c. build from 5 years ago, and I have no real plans to use it for anything other than that. I only hooked it up to the sawmill today because everything was there and I was curious to see if it had enough power to run it. By the time it had sawed a board off my spruce "log" it was getting hot enough that the accumulated oil on the cooling fins was beginning to smoke. I really don't plan on running anything with this engine.
                            Brian Rupnow
                            Design engineer
                            Barrie, Ontario, Canada

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                            • #15
                              Originally posted by brian Rupnow View Post
                              and probably I'm the only guy that ever sheared that pin off.
                              Clumsy bastard.
                              .

                              Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



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