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Simple Question about engine timing

  1. Dec 15, 2009 #1
    Im looking at designs for a engine, but im giving myself a headache over something which is probably incredibly obvious. Ill explain it as simply as I can in text and ive drawn a (terrible) paint image to help explain it a bit better.

    There are two cylinders. One cylinder needs to have its piston position 90 degrees offset to the other cylinder. If the cylinders are mounted at 60 degrees to each other, does the crank offset for the second cylinder need to be 90 degrees offset or 30 degrees offset?

    Last edited: Dec 15, 2009
  2. jcsd
  3. Dec 15, 2009 #2
    What do you mean by the following?

    One cylinder needs to have the travel of the piston
  4. Dec 15, 2009 #3
    Urgh im sorry that doesnt make any sense. Ive edited it now, I hope it makes more sense.

    Its basically a 90 deg phase angle between the two pistons
  5. Dec 15, 2009 #4
    You would need a 30 degree offset, to bring it up to the 90.

    90 degree V6's have a split/offset crank jounals to allow for even firing, as the natural angle for a V6 offset is 120 deg with a 3 throw crank, and 60 degress with a 6 throw crank.
    Last edited: Dec 15, 2009
  6. Dec 15, 2009 #5
    Ah see I would have been more inclined to say it still needed a 90degree offset because the position of the cylinder around the circumference doesn't seem to have an affect on the pistons phase.
  7. Dec 16, 2009 #6
    Just to also run this past you, when it says a 90 degree offset, I guess that is the same as saying 1/4 offset?
  8. Dec 16, 2009 #7
    I'd guess so.
  9. Dec 17, 2009 #8
    Im really stuck here, I asked my friend and he said this:

    Can I get a second opinion on this to make sure I dont do it wrong.
  10. Dec 17, 2009 #9
    Ok before we carry on, I need to know a lot more information.

    What engine are you doing this for?
    Can you give it's geometry (block offset, vee?, inline?, number of cylinders etc)
    How are you altering the crank angle and do the conrods share a crank pin?, (eg, is it using 1 throw crankshaft or 2 throw?)
    What do you mena by engine timing, do you mean then the piston reached TDC?

    Also what is the goal of whatever it is you are doing? (even firing, odd firing etc etc?)

    I think we're going wrong on nomenclature, as phase, block offset and crank offset are all different things.
    Last edited: Dec 17, 2009
  11. Dec 17, 2009 #10
    Hi. Its a StirlingEngine. The offset between the crank pin and the centre axle is .625 inches (the travel of the piston is 1.25 inches)

    Hope the exert below from a website can clarify:

  12. Dec 17, 2009 #11
    AHHHH I see, it's a stirling. I thought you were talking about something like a V2 or Vtwin where both cylinders are powered and they needed to be timed to be fire correctly.

    Yeah I agree with what your friend says.
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