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Thread: Prop Nut loosens

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  1. Prop Nut loosens 
    #1
    Join Date
    01-27-2008
    Location
    Whidbey Island, WA
    Posts
    13
    I seem to be having trouble with several engines, both 2 strokes and 4 strokes. Especially if I put on a plastic spinner, I can not keep the prop nut tight. Whether or not I use a chicken stick or electric starter for starting, the nut comes loose.

    Even without a spinner and backplate I seem to have some trouble keeping a prop nut tight while starting. Latest problem is a Magnum .91 4 stroke on a Flyin' King. Any suggestions appreciated. FF
     

  2.  
    #2
    What is happening:

    A) as you spin the prop with a starter, the starter is trying to spin the nut off.

    B When you are hand flipping (chicken stick or fingers) if the engine backfires, the prop carrying forward as the crankshaft reverses loosens the nut.

    Get some fine drywall sanding grid (looks like window screen, acts like sandpaper) Cut discs to fit. Put a disc on each side of the spinner backplate. This helps keep the prop and spinner from slipping and will REDUCE how often the nut comes loose.

    4-strokes are worse about this than 2-strokes. Its usually a sign of improper fuel mix in the 4-stroke. (over-priming will do it...)

    A 4-stroke can also throw the prop off if its lean on the top end. No warning. It can toss the prop right after starting... durring takeoff... or at any other point in the flight. The discs won't help.
     

  3.  
    #3
    There is an alternative starting method that reduces the issue... but it needs to be demonstrated in person to be sure you understand it.

    Your position relative to the plane and the prop orientation as it enters compression BACKWARD are key to it working and being safe.

    Using the tips of your first and middle finger bring the prop backward into compression. As the engine fires it will take the prop away from you and your fingers will spring out of the way automatically. (your position and how you place the fingertips on the prop are important...) the engine usually starts up first flip if its properly tuned.
    This method the prop nut almost never loosens.
    You never handle the sharp TE of the blade.
     

  4.  
    #4
    Join Date
    09-04-2011
    Location
    Oregon Ohio
    Posts
    10
    If you are using a jam nut or a second nut for your spinner to attach to make sure you are tightening them correctly.

    Tighten the first nut down to hold the prop. Then spin the second one down. Hold the first nut with a wrench as you tighten the second nut against it. If you don't the second nut will turn the first nut into the prop and not put tension between the two nuts.

    A 4 cycle should always have a proper jam nut.

    If you have a well used engine you might want to try new nuts.
     

  5.  
    #5
    Join Date
    01-27-2008
    Location
    Whidbey Island, WA
    Posts
    13
    Get new nuts!!! Oh, I get and thank you guys for the suggestions. I will try the washers out of sanding grid. I have managed to get thru the breakin process on the Magnum and if the weather is good today I will attempt the maiden flight.

    On a side note, I installed a smoke system for the Flyin' King, a first for me. This plane is on homemade floats but before I can try out the smoke system I am waiting for a replacement "gear" switch from Hitec. Somehow I managed to break off the toggle part of the switch and need to now replace the entire switch, grrrrrr.
     

  6.  
    #6
    Smoke oil will find EVERY seam in the covering and creep under. Seal the seams with clear Lustercoat.

    Clean the area to be sprayed using windex and a green dish scrubbing pad. And then wipe with a paper towel dampened with acetone. That guarantees the paint will stick to any of the iron-on film coverings.

    If you don't seal the seams you will be sorry.
     

  7.  
    #7
    Join Date
    01-27-2008
    Location
    Whidbey Island, WA
    Posts
    13
    Ok, I am back in Baja for the winter, actually got here first of Nov, but just now getting around to some r/c flying. I am having the same problem I had in BC but it is with an OS .61 that I can't start because it loosens the prop nut when I either flip the prop or use an electric starter. I can't believe that this engine is giving me grief as it always was an easy starting and great running engine. This is very frustrating, and being located in southern Baja , there is absolutely NO support down here. Hope somebody can help me. Thanks, FF
     

  8.  
    #8
    Join Date
    08-19-2002
    Location
    Wichita, ks
    Posts
    27
    How tight are you tightening the nut? I usually go to the point were I'm worried about breaking something...

    -Eric
     

  9.  
    #9
    You can go too tight and damage stuff... If you are making an impression of the washer in the prop you are cranking down too hard.

    Constantly throwing props usually has something to do with the engine being tuned wrong... or slick spinner back-plates.
     

  10.  
    #10
    Join Date
    01-27-2008
    Location
    Whidbey Island, WA
    Posts
    13
    Another day and another frustrating attempt to start this engine. I switched to a wooden prop, put abrasive drywall grid washers on both sides of the prop, am not using a spinner so no backing plate, tightened the nut as tight as possible, AND even with just a small squirt of fuel into the carb and NO glow igniter, I flipped the prop over a few times and the nut loosened.

    I then retightened the nut, finger over the carb and turned prop over to prime the fuel line, put a small amount of fuel into the carb, and then tried to flip backwards. Would get a small pop but no indication it wanted to run either direction.

    I even cut small hatch marks on both sides of the prop hub to try and get more grip on the washer/nut. What is next???
     

  11.  
    #11
    Join Date
    08-19-2002
    Location
    Wichita, ks
    Posts
    27
    Maybe try a bit of grease on the threads so that you're applying more clamping force and not trying to just overcome the friction of turning the nut?

    Could also try a bit of loctite but it's really not fun to get it all apart or re-tightened after using loctite... The engine wants to spin instead of turning everything off the assembly.

    Another thing I saw once was the thickness of everything wasn't enough to keep the nut on the threads. It was running into the prop-supporting smooth portion of the crankshaft. You'll never get it tight that way. Another washer fixed this problem.

    -Eric
     

  12.  
    #12
    Join Date
    01-27-2008
    Location
    Whidbey Island, WA
    Posts
    13
    Thanks Eric, I will try some grease and check to make sure the nut isn't bottoming out. I am getting nervous that I am running out of new ideas!!
     

  13.  
    #13
    Join Date
    08-19-2002
    Location
    Wichita, ks
    Posts
    27
    Quote Originally Posted by floatflyer View Post
    Thanks Eric, I will try some grease and check to make sure the nut isn't bottoming out. I am getting nervous that I am running out of new ideas!!
    There's only so many things it could be... lol

    We'll find it.

    -Eric
     

  14.  
    #14
    Some props are more resistant to slipping than others... Most black nylon props tend to be more prone to slipping than wood. (varies with the quality of the black nylon and the quality of the wood) Wood will slip more than APC grey composite.
     

  15.  
    #15
    Join Date
    01-27-2008
    Location
    Whidbey Island, WA
    Posts
    13
    Well guys, with all of your help I got the engine running today!! A tech from OS engines/Hobbico also suggested using Lok Tite. After using a Master Airscrew and wooden props, I went to an APC prop, added my abrasive washers, cleaned the threads, and added Lok Tite. Let it set up overnight and this morning got a successful start and run. I hope that this proplem is behind me. Thanks to all that responded. FF
     

  16.  
    #16
    Join Date
    02-18-2013
    Location
    luna, NM usa
    Posts
    26
    Well, I had that same problem with a new OS .40 LA, so I stuck a screwdriver in the nut wrench, and pulled it down pretty hard, I've had no more problems since then, I use a nylon 10-6 prop BTW. Just how I does it.
     

  17.  
    #17
    Join Date
    11-14-2002
    Location
    Weatherford, TX USA
    Posts
    28
    Grasp the prop with one hand and use a wrench to tighten the prop. Torque the hell out of it.

    Kick backs cause props to come loose. That is generally the result of lean settings. Richen up your high speed needle valve a half turn or so (even if it is rich) the engine will start. Once running reset the high speed needle valve to 300 or so RPM richer from the max setting. If you do not have TACH, set the engine at max RPM by ear and then turn the needle out a quarter of a turn. You will hear the engine slow down a bit.

    In the air the engine runs faster and needs more fuel. So by richening a little on the ground you will be near to perfect setting in air.
    Chip
     

  18.  
    #18
    In lieu of loktite I would go with a second nut jammed against the first to lock everything up.

    As stated in a previous post, hold the first nut with a wrench while tightening the jam nut.

    Thin nuts can be found at most hardware stores if room is needed inside a spinner.

    Hope this helps.
     

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