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Thread: Rupnow Overhead Cam-Air Cooled

  1. #1
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    Default Rupnow Overhead Cam-Air Cooled

    This morning I'm setting around with some free time, and I've been thinking for a while now about an overhead cam air cooled engine. There are a lot of horizontal and vertical cylinder engines out there, but I haven't seen very many single cylinder engines like the old "Iron Horse" washing machine engines with the cylinder on a 45 degree angle. My thoughts of course, were that if you could hang the entire camshaft off the cylinder head, then it would give you the freedom to run the cylinder on just about any angle you wanted. By using a cogged belt drive to the camshaft instead of a gear train, that opens up even more freedom with placement of components. I looked through all of the engines I have built over the past few years, and ended up leaning heavily on my Atkinson for some of this, so if it looks a bit familiar, then that is why. I'm not saying I'll actually build this, but you know how it is------Brian
    Brian Rupnow

  2. #2
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    That would certainly be entertaining to watch while running.

    I'm wondering how you would alter the valve clearance. Is the brown cross piece with the red followers intended to be fitted with different length followers? Or would you just use that as access room when removed to switch out the yellow buckets for different end thicknesses?

    I'm thinking it would be much less work to make and switch the red followers. Is that what you're thinking too?

  3. #3
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    Oct 2014
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    South Florida
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    most auto 4cyl ohc engines have been using timing belts for many years now, and they work ok. They do wear and need replacement after many miles however.
    If ur building for entertainment, u might look into desmo valve system as well. Those things have always fascinated me since Ducati started producing them many years ago. I can see all kind of temperature related problems with them, but they seem to have worked them out.

  4. #4
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    Those little red pill shaped "followers" would have to have some means of length adjustment.--Maybe. Really, the only thing you adjust them for is to have adequate clearance (valve lash) from the end of the valve when the valve is fully seated. It might be an issue of making one "close" to the right length, putting it in place, and measuring the resultant "clearance" with a feeler gauge, then either grind a little off one end or make a new one a little longer as measured by a feeler gauge.
    Brian Rupnow

  5. #5
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    Quote Originally Posted by brian Rupnow View Post
    Those little red pill shaped "followers" would have to have some means of length adjustment.--Maybe. Really, the only thing you adjust them for is to have adequate clearance (valve lash) from the end of the valve when the valve is fully seated. It might be an issue of making one "close" to the right length, putting it in place, and measuring the resultant "clearance" with a feeler gauge, then either grind a little off one end or make a new one a little longer as measured by a feeler gauge.
    Exactly. I'm likely dreaming up issues for later that would not exist. It's not like model engines run hard, fast or for enough hours that new pins are likely to be needed. So a one time trimming during construction as you suggest and they'd be good for our lifetime and someone else's to boot.

  6. #6
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    Quote Originally Posted by brian Rupnow View Post
    Those little red pill shaped "followers" would have to have some means of length adjustment.--Maybe. Really, the only thing you adjust them for is to have adequate clearance (valve lash) from the end of the valve when the valve is fully seated. It might be an issue of making one "close" to the right length, putting it in place, and measuring the resultant "clearance" with a feeler gauge, then either grind a little off one end or make a new one a little longer as measured by a feeler gauge.
    Include a means to attach a piece of feeler gage stock so that it stays between the cam and the follower so that the cam rubs on the feeler stock. Now it's easy to adjust, just find the right thickness and screw it in place and leave it there.

  7. #7
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    Or you could make them screw-on caps, then loc-tite them in position.

  8. #8
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    Quote Originally Posted by john hobdeclipe View Post
    Include a means to attach a piece of feeler gage stock so that it stays between the cam and the follower so that the cam rubs on the feeler stock. Now it's easy to adjust, just find the right thickness and screw it in place and leave it there.
    A setup where such shims replace the followers and actually ACT AS the followers would be an option. The idea is that some way is needed to prevent the cams running directly against the valves and having the valve stems end up experiencing side loading.

    Really though it's pretty simple to make up one follower that we know is too short then measure the clearance with feelers and make up two more that are spot on length to provide a thou or two of clearance.

  9. #9
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    "I'm not saying I'll actually build this, but you know how it is------Brian"

    In the spirit of the film Field of Dreams.....

    Brian, if you build it, it will run

  10. #10
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    I'm not saying I'll actually build this, but you know how it is------Brian
    I've seen this behavior pattern in you before. You say just spit balling, toying with an idea, not really planning to build it, blah blah blah. Next thing we
    know, 3 or 4 pages into the thread, there's chips a flying and swarf scattered everywhere.

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