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Thread: Hit and Miss engine question

  1. #1
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    Default Hit and Miss engine question

    Why did sideshaft hit and miss engines use helical gears between the crankshaft and camshaft. Why not bevel gears. I don't know, and would love to find out.---Brian
    Brian Rupnow

  2. #2
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    I'll take a stab at it......
    Helicals and spiral gears generally run smoother and quieter than straight cut gears.
    Helicals and spirals seem to have a longer lead in and lead out of gear meshing, than straight cut.

  3. #3
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    I wonder if it might have something to do with the irregular pulsations from a hit-and-miss engine. To minimize shock loading the timing gears should be as free from backlash as is possible. But if this is the reason, bevel gears would seem to have an advantage over helical gears; the backlash could be adjusted with a simple shim, or perhaps a Belleville washer.

    So much for that theory.
    Last edited by aostling; 06-08-2019 at 01:00 AM.
    Allan Ostling

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    Agree with Ringo, helical will be quieter and smoother than bevel. This is probably a stretch and no idea if this was a factor, but unless you have the bevel gear generator, correct helical gears might have been easier to manufacture. You can make helical gears on a (universal) mill (although not sure at that angle) where as a bevel gear requires a special generation machine to achieve the correct tooth form. My guess is more would be made in house as supplies chains, communications and transportation were a fraction of what they are now
    Last edited by Mcgyver; 06-08-2019 at 07:36 AM.
    .

  5. #5
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    I’d guess that the helical gear set gave the designers more opportunities to move the cam drive shaft under the centerline of the crank shaft, freeing space up at the head.

    Sid

  6. #6
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    since we on subject of gears,
    when you look at gears, straight cut with small number of teeth, they look like they only mesh the 1 tooth that is fully engaged, all other teeth look like they still have backlash in open state.
    when you look at spiral or helical, it looks like more than one tooth is beginning to take up backlash earlier than the tooth before it, and with that 1 tooth fully engaged, it looks like the tooth before and after that 1, is 99.9% engaged.
    Am I explaining this good enough for what I think I see?
    and, is this the way helicals really work or no?

  7. #7
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    Lots of good guesses here. I think it is probably based on the fact that with helical gears you simply have a longer tooth engagement, but that is only a guess from my side.
    Brian Rupnow

  8. #8
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    Quote Originally Posted by aostling View Post
    I wonder if it might have something to do with the irregular pulsations from a hit-and-miss engine. To minimize shock loading the timing gears should be as free from backlash as is possible. But if this is the reason, bevel gears would seem to have an advantage over helical gears; the backlash could be adjusted with a simple shim, or perhaps a Belleville washer.

    So much for that theory.
    Explain the shock loading?
    Since the engine is always turning, the gear teeth would always in contact wouldn't they? Maybe above or below the optimum rpm, but the engine is still rotating whether it's firing or not.

  9. #9
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    Axial movement of a helical gear allows angular adjustment.......

    Bevel gears require a different machine, helical gears only need a milling machine with attachments.

    I think some DID use bevel gears, however. I'd have to look for the examples
    1601

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    Hashim Khan

  10. #10
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    Just spinning the engine will not eliminate "backlash" unless your spinning at a fair amount of RPM, you have to keep in mind that it's a valvetrain subject to intermittent loading and actually propulsion from the valve springs once they get on the other side of the cams lobe.

    so how do you eliminate the backlash? in the case of conventionally driven gears you split one of the gears and take about a third of it, spring load it with it's mate and then "install it" into its meshing counterpart, the best of both worlds is doing this with a helical style set, now you have quiet running in both gear function and backlash elimination regardless of expansion ratios...

    this would be a bit of a hat trick with helical/beveled

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