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    • CommentAuthorkamran
    • CommentTimeDec 1st 2011
    Hello all
    For a single cylinder 1" bore X 1.5" stroke 4 cycle low compression slow running engine
    Is there a formula to determine the length of the piston, the length of the
    cylinder and the length of crank rod?

    Also for example, does it matter if the bottom edge of piston is .125" above the
    bottom edge of the cylinder vs .25" above?
    Or even does it matter if the bottom edge of the piston is .125" or .25" below
    the bottom edge of the cylinder?

    • CommentAuthordavid
    • CommentTimeDec 2nd 2011
    Have you looked in Google books searching for stationary engine design?
    • CommentAuthorkamran
    • CommentTimeDec 2nd 2011
    Thanks David,
    Found some interesting stuff in google books.
    Hey Kamran!

    What did you find out? I have always tried to design so the piston stays in the bore. I'm sure the piston can come out a small percentage but did you find anything in the books to define how much?
    • CommentAuthorkamran
    • CommentTimeDec 9th 2011
    Hi Steve,
    Didn't find much on how much of skirt can go below bore in a full scale engines. But for model I don't think this really matters because of the amount of running time and load. So for model can we limited to the wrist pin?
    • CommentAuthorgbritnell
    • CommentTimeDec 10th 2011
    I think the engineering idea behind the piston running out of the bore came from steam engine design. On most riding surfaces you want some overlap so that it doesn't wear an edge where the sliding part stops against the fixed part. If you've eve seen a high mileage engine there is a ridge where the rings reach the end of their travel in the bore. This is unavoidable but in some cases of over-revving could cause the ring to pound out the ring land in the piston.
    Here a couple of lengths FYI

    GADE 1/4 Scale
    Bore 7/8"
    Here are a couple of lengths FYI

    GADE 1/4 Scale 1 1/2 HP
    Bore 7/8" Stroke 1 1/4 skirt below bore 1/16"

    Fairbanks Morse 3 HP Z Full Size
    Bore 4 1/2" Stroke 6" Skirt below bore 1 5/8"

    Hope it helps