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

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  • Originally posted by Jim Stewart View Post

    How old are you talking about?

    My first bike was a Harley (it was all I could afford) - 1936 EL (61 CI). It had a battery/coil ignition and the spark retard/advance was on the left twistgrip. A couple of times I forgot to retard the spark when starting and the beast threw me over the bars. Or nearly. I learned.

    -js
    Flatheads, knuckleheads and pans, all with magnetos. But then most of the ones I ever dealt with were choppers, there wasn't anything in the handgrips except for the throttle.
    25 miles north of Buffalo NY, USA

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    • -This engine has no governor, but before I made my trials with it I had turned the throttle adjustment screw in to the point where the engine was running at about 2000 rpm. The edger grabbed the board and sent it through the first set of powered rollers, then about 3" thru the saw, and then when the board got to the second set of rollers the engine bogged down and quit. I will retry it later this week with a weaker set of springs on the last set of powered rollers.
      Brian Rupnow
      Design engineer
      Barrie, Ontario, Canada

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      • I have also investigated adding a manual ignition advance. It can be easily done, but I've hurt my back and I'm setting here designing with a heating pad on my back.
        Brian Rupnow
        Design engineer
        Barrie, Ontario, Canada

        Comment


        • I would expect an engine to bog down and stall without a governor to open the throttle under significant load. The throttle is essentially a power (or torque) control, so at idle or free running at any given speed, it supplies just enough air/fuel mixture to overcome friction and windage from the fans. How far open is the throttle? Can you manually open the throttle as it starts to bog down? Or maybe preset it to 3000 RPM and it might slow down to the desired 2000 RPM when it starts to feel the load.

          Sorry to hear about your back.
          http://pauleschoen.com/pix/PM08_P76_P54.png
          Paul , P S Technology, Inc. and MrTibbs
          USA Maryland 21030

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          • Paul---It's a lot easier to add a manual ignition advance to the engine than it is to add a governor. I have no idea what did to my back. As far as I know I didn't lift anything heavy or bend any strange direction. I've had bad backs before, and eventually they fixed themselves.
            Brian Rupnow
            Design engineer
            Barrie, Ontario, Canada

            Comment


            • Originally posted by PStechPaul View Post
              I would expect an engine to bog down and stall without a governor to open the throttle under significant load. The throttle is essentially a power (or torque) control, so at idle or free running at any given speed, it supplies just enough air/fuel mixture to overcome friction and windage from the fans. How far open is the throttle? Can you manually open the throttle as it starts to bog down? Or maybe preset it to 3000 RPM and it might slow down to the desired 2000 RPM when it starts to feel the load.

              Sorry to hear about your back.
              Paul is 100% correct about the need and functioning of a governor. Just about every small engine has a governor for those exact reasons. From no load to loaded the carb must be opened further to maintain RPM. If you unhooked the governor on your lawnmower and set it for 3000 rpm it would likely stall as soon as you got into some heavier grass because the throttle didn't open more to accommodate the increased load. The edger bogging down and stalling under load is quite predictable, the two big flywheels probably helped get it even that far into sawing the board.

              If the load is steady and continuous a governor isn't needed, something like a fan or propeller for example. The edger is a widely varying load as well as engaging the clutch itself.

              Now IF the engine is bogging and stalling with the carb wide open, thats a different matter !

              Ignition timing may help somewhat buts its not going to overcome the need to vary throttle / carb opening under varying loads.

              Surely Brian is aware of these things even if he wants to hope he can get by without a governor. As Brian said, its easier to add a manual ignition advance than a governor, but its NOT a substitute.
              Last edited by Sparky_NY; 05-08-2020, 05:36 PM.

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              • Originally posted by brian Rupnow View Post
                Paul---It's a lot easier to add a manual ignition advance to the engine than it is to add a governor. I have no idea what did to my back. As far as I know I didn't lift anything heavy or bend any strange direction. I've had bad backs before, and eventually they fixed themselves.
                Brian I had the same problem about a week ago. One day I was quite busy - walked up to the mail and back, mowed the lawn and a few other things. The next morning I got up and a nerve in my lower back wanted to spasm every time I moved. Sitting didn't help because it would cease up even more. So I just walked slowly around the house and up and down the drive way. That gets pretty boring quickly. Needless to say I didn't even see the inside of my shop for about 3 days. It gradually went away and I am back at it again now. Considering I spent most of my life working on heavy equipment I guess I just have to put up with this sort of thing once in a while. One thing for sure it beats the heck out of getting that virus. Take care and there are better days ahead.
                Larry - west coast of Canada

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                • It might be simpler..... what is different at the time it stalls? I suggested above that there might be a misalignment that jams things when the wood gets to a certain point, and Brian mentioned that it is right about when it hits the second set of rollers. They are powered rollers, but if they have strong springs, they might not open up easily, and so jam the works.

                  Yes, ideally the governor and all that, but it ought to work anyhow, unless the carburetor is really simple. And even then, the old hit and miss engines often had no "carburetor", just a crude "mixer", yet they worked OK driving shingle cutters and so forth..
                  CNC machines only go through the motions

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                  • When an engine idles, whether that be low idle or high idle the only power it produces will be the power that is required to keep it turning and no more, hence the term idle.
                    It only takes a very small throttle opening to do maintain an idle and there isn't much extra available power to take on any additional load.
                    So we need either a governor to sense when that load slows down the engine or an operator to man the throttle.

                    Brian can you be that governor/operator in order to increase throttle opening? The engine certainly seems healthy enough by the sound of it to do what's required. I'm sure that this will put to rest any question about the engine's capabilities.
                    Home, down in the valley behind the Red Angus
                    Bad Decisions Make Good Stories​

                    Location: British Columbia

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                    • Originally posted by brian Rupnow View Post
                      I have also investigated adding a manual ignition advance. It can be easily done, but I've hurt my back and I'm setting here designing with a heating pad on my back.
                      Sounds like you've been having fun but really, I could easily see a set of castings as a kit... maybe thats just me dreaming, I think this engine is just plain sexy and deserves it!
                      25 miles north of Buffalo NY, USA

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                      • Brian already HAS a governor on that engine.

                        He has two fans, with a power law response, so whatever speed he sets it to will be governed to the degree that a slow down will remove fan power at more than a linear rate, and allow that power to go into sawing wood.

                        I do not know HOW effective that is, Brian said he has less airflow than he expected, but if the fans move reasonable air, it should have an effect. It will depend on how much extra power is required to get past that "tight spot" in the sawing cycle.

                        Originally posted by Willy View Post
                        When an engine idles, whether that be low idle or high idle the only power it produces will be the power that is required to keep it turning and no more, hence the term idle.
                        It only takes a very small throttle opening to do maintain an idle and there isn't much extra available power to take on any additional load.
                        So we need either a governor to sense when that load slows down the engine or an operator to man the throttle.

                        .......
                        The presumption is that since it WILL saw the wood, that the throttle is opened enough to do that. Some ADDITIONAL load at THAT particular point in the "saw cycle" is stalling it.
                        Last edited by J Tiers; 05-09-2020, 02:13 PM.
                        CNC machines only go through the motions

                        Comment


                        • Originally posted by J Tiers View Post
                          Brian already HAS a governor on that engine.

                          He has two fans, with a power law response, so whatever speed he sets it to will be governed to the degree that a slow down will remove fan power at more than a linear rate, and allow that power to go into sawing wood.

                          I do not know HOW effective that is, Brian said he has less airflow than he expected, but if the fans move reasonable air, it should have an effect. It will depend on how much extra power is required to get past that "tight spot" in the sawing cycle.

                          The presumption is that since it WILL saw the wood, that the throttle is opened enough to do that. Some ADDITIONAL load at THAT particular point in the "saw cycle" is stalling it.
                          I think the loss of power to drive the fans at a somewhat lower speed would be negligible and have little to any effect. The parasitic engine pumping loses would likely be far greater than the fan's power requirements at a reduced speed. Even the combination of the two is not enough to have any noticeable affect in the engine's ability to maintain any increase in the load at the point it is stalling at.

                          You may very well be correct in the presumption that perhaps the "saw cycle" itself is hitting a wall.
                          I'm sure Brian will diagnose the issue and find a solution, he seems to be very capable of finding the root cause of obstacles in his path.
                          Home, down in the valley behind the Red Angus
                          Bad Decisions Make Good Stories​

                          Location: British Columbia

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                          • Yes, the saw, once it is well into the wood, should not have any significant change in load. So something else must be happening, either jamming from misalignment, or hitting the rollers, or ????

                            A small fan that size takes a smallish shaded pole motor to run it, so there is a potential to have an effect from two of them. If he is not seeing much air movement, the effect is going to be less, as I mentioned.
                            CNC machines only go through the motions

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                            • What might be better and perhaps easier to implement would be a centrifugal clutch like that in a chainsaw or string trimmer. When the operator opens the throttle, the speed will increase to what is needed to engage the clutch, which adds sufficient load to keep it from overspeeding. Then the saw will have sufficient power to do its work, and if not, the clutch will disengage and prevent stalling. But I would enjoy the challenge of coming up with a microcontroller based electronic solution, which could easily implement spark advance, and throttle control by means of a solenoid. The latter would be little more challenging, probably needing a PWM drive to apply just enough current to move the armature to an intermediate position. A servo motor would be another interesting option. If I had such an engine to work on, I'd probably start working on it, but I'm not sufficiently motivated to build such an engine or get the incomplete one I bought running.
                              http://pauleschoen.com/pix/PM08_P76_P54.png
                              Paul , P S Technology, Inc. and MrTibbs
                              USA Maryland 21030

                              Comment


                              • Since I want to run Thumper at a much greater speed than at idle, I need to be able to adjust the timing of the engine. With a non adjustable ignition timing, the engine will run much faster than at idle, but it really doesn't have a lot of power at higher rpm. The cheap and quick way to address this is to mount the ignition points on a separate timing plate which can be adjusted with an attached lever. A #10 shcs and spring washer go thru the slot into the frame of the engine so the adjustable timing plate will hold itself in whatever position you set the handle at. This current set up will give an adjustment range of a total 120 degrees. It is pivoted on the crankshaft. This set-up will allow me to advance the engine timing when it is running at a higher speed. I have hidden the near side flywheel here so that the ignition advance mechanism is visible. The ignition points are attached to the timing plate and rotate with it, thus advancing or retarding the ignition.
                                Brian Rupnow
                                Design engineer
                                Barrie, Ontario, Canada

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