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The Crazy Engine Project

This is a discussion on The Crazy Engine Project within the Technical forums, part of the Caferacer.net Forums category; Ok Start Over. For all of you who have posted. I've read and considered them all, and will be incorporating many of them. In view ...

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  1. #1
    Moderator jbranson's Avatar
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    The Crazy Engine Project

    Ok Start Over.

    For all of you who have posted. I've read and considered them all, and will be incorporating many of them. In view of the major changes, and to prevent the topic from getting too long. I'm going to start it over now and then.

    For those who are just joining the conversation, you'll have to start here. Please reserve comments to those areas where you are familiar with the discussion.

    First the latest image. Then I'll comment in the next post.

    JohnnyB




  2. #2
    Moderator jbranson's Avatar
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    Right now I'm heading in the direction of a bevel gear drive off the top of the cam disk, down to the crank like a Ducati single. Or a chain/belt off the crank to a short bevel drive shaft to the disk.

    No way to avoid at least one 90 degree turn to get the rotation we need. Chain or belt to a short drive shaft would be the most efficient, but would require the most external parts. Full shaft drive from the crank would be the most compact, but would be quite complexity, precision, expensive and have at least two 90 degree turns which would be less efficient.

    I'll have to model up some reasonable intake and exhaust systems to see how much room we will have adjacent to the cylinder for a cam drive system.
    JohnnyB

  3. #3
    Moderator jbranson's Avatar
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    Right now I'm heading in the direction of a bevel gear drive off the top of the cam disk, down to the crank like a Ducati single. Or a chain/belt off the crank to a short bevel drive shaft to the disk.

    No way to avoid at least one 90 degree turn to get the rotation we need. Chain or belt to a short drive shaft would be the most efficient, but would require the most external parts. Full shaft drive from the crank would be the most compact, but would be quite complexity, precision, expensive and have at least two 90 degree turns which would be less efficient.

    I'll have to model up some reasonable intake and exhaust systems to see how much room we will have adjacent to the cylinder for a cam drive system.
    JohnnyB

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  5. #4
    Senior Member kenessex's Avatar
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    I like it so far. It does look fairly simple, so to complicate it a little, how about if each of the tappets had a roller on top to contact the cam track? As far as the cam drive goes, I still like the idea of a connecting rod from the outside of the flywheel to a bevel gear that meshes with another bevel built into the outer rim of the cam disc. I think it would be thin and compact as it goes up the side of the cylinder and you would only have to worry about setting the tolerances of one gear set.

    Ken
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  6. #5
    Moderator jbranson's Avatar
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    Ken, the rollers on the tappets might be a requirment if the lobe profiles are as radical as I think they will have to be.

    I have a couple of issues with the "reciprocating" solution to the cam drive. One is the stroke has to be very short if the system is to be compact, which means a whole lot of stress on the connecting rod/pins as it will have no leverage on the cam drive crank. Another is, unless the big end of this rod is quite large, it would have to go on the very end of the crank, which would not allow for any crank driven components on that side of the crank. If the rod is "inboard" of any crank driven components then the journal for the big end has to be larger enough to handle the loads induced by crank driven components. Another is receprocation is not very efficient, and it would also enduce complications in the crank balance.

    A shaft driven solution would just require a bevel gear on the crankshaft just outside the main main bearing. My guess is the Ducati went with a bevel drive, and then to belt for these very reasons.

    Bear in mind with a receprocating solution the "rod" would have to move at crank speed ...say 12,000 rpm. Whereas a geared, chain, or belt solution can be underdriven at the crank and turn the shaft/belt/chain a much less than crank speed. In this particular application, if the "rod" receprocated at crank speed it would require a 1:6 gear ratio at the cam disk... my gut feeling is that might not be possible with the dimensions of this engine....the drive gear at the cam disk would be too small to effectively mesh with the bevel on the cam disk. Similar to the way there are limits to differential ratios in a car .... imagine the ring/pinion set required to build a 6.00 rear end ratio in a car... unless the ring gear (differential casing) is huge... then the pinion is tiny and the loads are not spread over enough tooth area to provide the necessary strength or durability.
    JohnnyB

  7. #6
    Senior Member kenessex's Avatar
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    JohnnyB,
    All good arguments for using a shaft. Since I posted I have been Googling around for cam drives and the only reciprocating cam drive I found was on a 1929 4,5 blower Bentley. Not exactly the engineering model that we should always follow. Bevel drive is cool, too.
    I have been thinking about cam profiles. If we went with rocker arms, the we would not have to run 1:1 rockers and could get away with smaller lobes at the expense of some stresses on the longer side of the rocker. Somewhere in my mind I seem to remember something about 1.4:1 rocker ratios. Maybe that was a limit or maybe just a number? I don't know.

    Ken
    WERA 119
    CCS 119
    CRA 119
    AHRMA not anymore
    \"Think twice before you speak, and then you may be able to say something more insulting than if you spoke right out at once.\"
    Evan Esar
    Newbies, Geeto and Tex (Bye Tex)hate me!!

  8. #7
    Moderator jbranson's Avatar
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    I've seen plenty of automotive rockers that are 1.65:1. Very common...almost standard to see 1.5:1.

    Ratioed rockers would help reduce cam lobe height, but would also increase the stress on the part I'm most worried about, the cam followers ...or cam side of the rocker. Besides friction between the cam and rocker, the side loading on the rocker would start getting silly too, although a rocker can tolerate it way better than a valve.

    In the setup in the image above the tappet support bore is so close to the contact point between them and the cam lobes that side load wouldn't be an issue. Then the tappet presses straight down on the valves so they see no side load at all.

    I still have to model a cam profile at a 1:6 ratio to see what the hell it looks like. Might not be doable at all with sprung valves, might have to go with some kind of direct acting system.

    This topic will be a long haul probably.
    JohnnyB

  9. #8
    Moderator jbranson's Avatar
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    Latest image showing how I imagine the cam disk bearings might be arranged. Having a heck of a time creating custom hardware like bearings and giant thin jam nuts that are not standard parts available in the library.
    JohnnyB


  10. #9
    Moderator jbranson's Avatar
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    Another update showing a possible cam drive. Simple spur gear that can have a shaft that travels down to a bevel gear set on the crank.
    The image shows the cam disk and large drive gear as separate parts, but they could be combined ...but it would be nice if you could replace them independently for wear or cam changes. They could be joined by indexed pins that would allow for cam advance and retard.

    With the setup shown the drive shaft from the crank would turn crank rpm. I'd rather cut that in half with a 1:2 ratio at the crank, and then 1:3 at the cam. Which would mean the larger gear would be a bit smaller and the small gear a bit larger. That would also make the drive at the crankshaft 1:2 like any normal four stroke cam drive and so easier to work out timing and such.
    JohnnyB

  11. #10
    Senior Member TheGreg's Avatar
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    might be about time to clean up the thread...saw the new picture 2 times and had to scroll for a bit before i got to read about it...


    the way i see this it would work ok, maybe pretty well, until it was time to adjust something...then EVERYTHING would have to come off of the top to be able to get to anything...unless i guess adjusting the valves would mean tightening the large retaining nut on the top alittle bit?
    ask me about my ADD or pie or my cat. a dog. i have a bike. Do you like TV? i saw a rock. hi.

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