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Thread: NSI re-drive information

  1. #1
    lin_light's Avatar
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    NSI re-drive information

    I have a NSI re-drive on a Subaru EA81. I purchased it with a plane at an auction. The builder passed away in 2003 and I have no information on the ratio of the gear. The plane is about 1,000 to 1,200 lbs and is designed for 150 mph. Any way of judging the ratio? I have someone interested in purchasing the drive and want to know the ratio. Any information would be appreciated.

    Lin

  2. #2
    Mike Switzer's Avatar
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    I don't know if it is a gear or belt drive, but pull the cover & count the teeth on the gears or pulleys, then figure the ratio - but most will have a tag or a stamp somewhere that shows the ratio.

    (That goes for a toothed belt drive, if it is a straight v belt drive it is a little more complicated, the critical drive diameters will be stamped on the pulleys (it is hard to measure accurately) & you use them to figure the ratios)
    Last edited by Mike Switzer; 10-24-2011 at 10:17 PM.

  3. #3
    lin_light's Avatar
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    Gear driven. Think there is any issues opening up the case?

  4. #4
    Mike Switzer's Avatar
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    Probably not, it is probably just 2 gears with 2 bearings on each gear shaft. Drain the oil into something first, there should be a drain plug & a fill plug, if you just split the case you will have a mess if it holds a lot of oil.

    Depending on the size you might want to get a full or half size aluminum sheet cake pan to set it on when you open it. (Half sheet pans are approx 12 x 18 & you can pick them up cheap at Sams, full are approx 24 x 18 & you will probably have to order them)

  5. #5
    Mike Switzer's Avatar
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    Oh, another thing, there will be a seal where the shafts go thru the case, be careful not to damage them. Depending on their condition you may want to replace them anyway, they don't last forever & they are usually pretty cheap at the local bearing store / industrial power transmission supplier.

    A little Vaseline helps the new ones go on without damaging them
    Last edited by Mike Switzer; 10-25-2011 at 10:07 AM.

  6. #6
    lin_light's Avatar
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    Drive has never been used. Still attacted to the Engine where it was attached around 1997. Have some interested in it and wanted to know the ratio.
    I'm guessing 2is to 1

    Lin

  7. #7
    Matt Gonitzke's Avatar
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    If it's gear drive, can't you just index something on the crankshaft and something the prop flange, and rotate it by hand, counting the input and output revolutions? I don't see any reason to take it apart to determine the ratio.

  8. #8
    Mike Switzer's Avatar
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    Quote Originally Posted by Matt Gonitzke View Post
    If it's gear drive, can't you just index something on the crankshaft and something the prop flange, and rotate it by hand, counting the input and output revolutions? I don't see any reason to take it apart to determine the ratio.
    That works fine if it is something simple like 1.5:1, but if it something odd like 40:27 (1.379:1, just an example) you can't get the exact ratio

    If it is new there should be a tag on the outside that says what it is

  9. #9
    Matt Gonitzke's Avatar
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    I would think you could get close enough, if the different ratios they were made in are known, unless they made the different ratios so close together that you wouldn't be able to tell. If you were to turn it until both input and output stopped at an integer value of turns, it would be spot on. Might take a few minutes, but certainly faster than taking it all apart.

  10. #10
    Logic says
    1. Put a spanner on the crankshaft nut, start at TDC by the timing marks, mark the prop shaft and start winding.
    Count until the prop shaft has completed 1 rev, for an approximation. OR-
    Keep winding until both TDC and prop shaft coincide again BUT
    that may be 226 turns if the ratio is 2.26:1 (Builds big Muscles).
    2. If the motor can be run, an engine rev counter / prop blade counter would be easy math (your local A&P will have a prop rev counter, or Spruce sell them for about 30 bucks).

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