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Thread: Vertical hit and miss engine

  1. #221
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    Quote Originally Posted by brian Rupnow View Post
    Yes Larry, I probably will. The nice thing about this modification is that it can be added without changing anything that already exists. If it works, then all is well. If it doesn't I can remove it and nothing of the original build will be affected.
    For a future project, you could borrow ideas from a propeller governor on a small piston powered airplane. Same principles at play but adjustable on the fly.


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    Last edited by RB211; 08-25-2019 at 07:19 PM.

  2. #222
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    RB211--Looks a bit complex for me. The one I showed is also "adjustable on the fly". Any governor adjustment done when an engine is not running is just guess work.
    Brian Rupnow

  3. #223
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    It works!!! I have attached a still picture and a video showing my "fine tuning adjustment screw" that affects the rpm at which the engine kicks in and out of hit and miss mode.
    https://www.youtube.com/watch?v=y5I-vitFqUI
    Brian Rupnow

  4. #224
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    I've never had a real problem getting engines to run fast. I like my engines to run slow, and it takes more fiddling to get them to run slow than fast. In a perfect world, I'd like the hit and miss engines to fire once, then coast for seven or eight revolutions, then repeat. I have came to the conclusion that although Viton rings seal extremely well, the penalty for using them is that they create more drag on the piston than cast iron rings. This drag has a rather dramatic effect on how many coast cycles a hit and miss engine will have before it hits again. This engine has a pair of cast iron rings that purchased, and it does seem to have an improved coast cycle. The only thing wrong with having them run as slow as I like is that they lose the ability to take over and keep running when a load is applied.
    Brian Rupnow

  5. #225
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    Quote Originally Posted by brian Rupnow View Post
    I've never had a real problem getting engines to run fast. I like my engines to run slow, and it takes more fiddling to get them to run slow than fast. In a perfect world, I'd like the hit and miss engines to fire once, then coast for seven or eight revolutions, then repeat. I have came to the conclusion that although Viton rings seal extremely well, the penalty for using them is that they create more drag on the piston than cast iron rings. This drag has a rather dramatic effect on how many coast cycles a hit and miss engine will have before it hits again. This engine has a pair of cast iron rings that purchased, and it does seem to have an improved coast cycle. The only thing wrong with having them run as slow as I like is that they lose the ability to take over and keep running when a load is applied.
    Might try it with only one ring, or on the next motor. The ringed RC airplane engines only have one ring typically. (I never seen one with more but they might be out there).

  6. #226
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    The people who have purchased this engine plan set will be interested in details of this fine tuning adjustment for the hit and miss function. Rather than email every individual, I will post it here.





    Last edited by brian Rupnow; 08-27-2019 at 01:55 PM.
    Brian Rupnow

  7. #227
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    Brian, thanks for the fascinating project. I have hopes, after retirement, to get into building small IC engines; your designs give me a lot to think about.

    But at the moment, I am still very much a newbie, and I'm afraid my question is going to reveal that - but I'll ask it anyway:

    As I understand it from your design and the videos, the intake valve is actuated solely by the vacuum created when the piston descends. Is that correct? If it is ... what are the reasons for having an actively actuated intake valve in other engine designs?

    My apologies if these questions are out of line or obvious or silly ... as I said, total newbie here!

  8. #228
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    Awake--Nothing wrong or silly about your question at all. Vacuum operated intake valves work very well on low rpm engines. They have time to open and close and require no separate cam or rocker arm or push-rod. However, as engines became faster and faster as they developed, the vacuum operated valves just couldn't react quickly enough. This led to having a cam and rocker arm and pushrod to operate the intake valve. Most full size engines now rely on a cam to open the intake and exhaust valves, with a valve spring to close them. Even that has limitations. Some of the really high rpm engines that have been developed have cams to close the valves as well. I believe they are "desmodronic" valve trains.
    Brian Rupnow

  9. #229
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    Quote Originally Posted by brian Rupnow View Post
    Awake--Nothing wrong or silly about your question at all. Vacuum operated intake valves work very well on low rpm engines. They have time to open and close and require no separate cam or rocker arm or push-rod. However, as engines became faster and faster as they developed, the vacuum operated valves just couldn't react quickly enough. This led to having a cam and rocker arm and pushrod to operate the intake valve. Most full size engines now rely on a cam to open the intake and exhaust valves, with a valve spring to close them. Even that has limitations. Some of the really high rpm engines that have been developed have cams to close the valves as well. I believe they are "desmodronic" valve trains.
    Then there's top fuel dragsters where things happen so fast with such violence that no one including Kalitta really know what's going on?

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  10. #230
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    Lowest record elapsed time for the quarter mile is 3.7 seconds--either a top fuel dragster or a funny car. I find that unbelievable. When I ran the front engine dragster back in the mid sixties low 13 second runs were the order of the day.
    Brian Rupnow

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