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  1. #1

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    Pinion Gear Keeps Falling Off. Help

    The pinion gear on my Losi eight 3.0e keeps falling off and striping my spur gear. I have already torn up $20 worth of spur gears in 2 days. I use $40 set of Dynamite hex drivers to torque down the set screw on the flat part of the shaft and I use red Loctite. After letting it setup for about 25 minutes I can go on the track and after 2 laps it falls off, strips a spur gear. Whats the problem? How do I get this pinion gear to stay on the rod?

  2. #2
    EXT2Rob's Avatar
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    I'm not sure 25min is enough. Unless you're using excellerant . You should let a freshly-glued grub-screw sit for at least a few hours. If not longer.

    Is the flat part of the motor shaft still OK? How are you setting the mesh? (Using the ol' paper trick is a good idea)
    Just a schmoe....

  3. #3

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    Yeah the flat part of the shaft is fine. Maybe the the Loctite just needs to set up longer like you said. Also all the set screws that come with these pinions kinda come to a point then go flat. Last night I grinded one flat on the end and loctited it in there. We'll see how that does. If it works I'll grind all my pinion set screws flat for now on.

  4. #4
    phmaximus's Avatar
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    Yeah I don't think using red loctite on a grub screw is the smartest idea, It is only removable once cured by heating up parts to 500F (260C).

    id recommend Blue 242, and follow the instructions... Ie, Sets in approximately 10 minutes and fully cures in 24 hours.
    LOSI: 5IVE-T, 8IGHT-E, MICRO SCT
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  5. #5
    Maj_Overdrive's Avatar
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    I've never had to use anything more than a drop of Blue on the set screw for my pinions. You could try using some blue between the pinion and motor shaft as well.

    Maybe I got lucky the one time I had a pinion fall off, but it didn't chew up the spur gear when it came off. Is your motor aligned to the spur or is it off? Usually changes in gear mesh is what chews up spurs.
    Punch Control? I don't need no stinking Punch Control!

  6. #6

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    I mesh the pinion to the spur with the pinion bottomed out sitting in the spur. Then I back off just a hair where theres a slight, little, wobble back and forwards between the pinion and spur but just a slight little space. Its just enough to put your finger on the spur and tick it back and forwards a little bit. Yeah same problem today. After just two batteries the pinion that had a flattened set scew in it that had been red loctited and set up over night (24hrs) came off again. Thankfully it didn't slip off while I was running and strip a spur gear but when I was done running I checked it and it just slipped off. Come right out like a loose tooth. I am truly out of ideas now. I guess it will have to be one of them things I check after every run.

  7. #7
    EXT2Rob's Avatar
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    That is just wrong. It should not do that. Especially using loktite. I've never heard anyone have such an issue, except for the very first time they run, and discover the grub screw wasn't loktite'd. The only thing I can think of is that the Red Loktite is too brittle for the job, and that Blue would do better. I always use Blue and I have never ever had a problem like this.
    Just a schmoe....

  8. #8

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    I think theres a lip on the rod near the motor where the flat part ends. Maybe the set screw was on that lip and it wasn't bottoming out on the flat part of the rod. I turned the pinion around so the set screw and collar are toward the end of the rod not towards the motor. After 2 packs thru it today it didn't move so Im hoping that's the solution. Either way theres no way to mesh the gears together perfect and have that set screw on the rod. The pinion will over lap the spur at least 1 or 2 mm to one side or the other. I don't know if that's the cars fault (losi) or the motors fault (castle creations).

  9. #9
    phmaximus's Avatar
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    It's very easy to work out what happened...
    when the pinion came adrift, was the grub screw still glued in with loctite??? Or was it loose and easy to re tension with hand tools
    Because using red locktite that grub screw should of been stuck... To the point that with no heat a hex driver would simply strip and round if u tried to remove it.

    im suspect that there is a issue with how much loctite u are using, strength, and it's cure times

    using red locktite is not the smartest idea, u might want to re thing that. Otherwise down the track u might have issues removing it.
    LOSI: 5IVE-T, 8IGHT-E, MICRO SCT
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  10. #10
    EXT2Rob's Avatar
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    Quote Originally Posted by BlueBorderRC View Post
    I think theres a lip on the rod near the motor where the flat part ends. Maybe the set screw was on that lip and it wasn't bottoming out on the flat part of the rod. I turned the pinion around so the set screw and collar are toward the end of the rod not towards the motor. After 2 packs thru it today it didn't move so Im hoping that's the solution. Either way theres no way to mesh the gears together perfect and have that set screw on the rod. The pinion will over lap the spur at least 1 or 2 mm to one side or the other. I don't know if that's the cars fault (losi) or the motors fault (castle creations).
    Ah HA, so you figured it out. Good. And, it's OK that the pinion over-hangs the spur, side to side. As long as the spur doesn't over-hang the edge of the pinion.
    Just a schmoe....

  11. #11
    phmaximus's Avatar
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    oops missed that part, sounds like its getting there... awesome.

    hey just thinking, im concerned about this overhang... if its overhand is because the pinion teeth are physically wider than the spurs teeth than that does not matter.
    but...
    if the overhang is because the gears are misaligned that's not good... might need a different brand pinion with the grub screw closer to the gear

    I hope u get it going, im keen to know what u think?
    im running a 8ight 2/0 EU converted to brushless and I love it.... I don't know why I didn't get one years ago???
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  12. #12

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    Your right the gears are the same width but like I said theres no way to get it perfectly meshed and have that set screw on a flat part of the rod. Maybe a different pinion gear is a good idea? Would it hurt anything to put a couple washers behind the motor mount between the motor and the mount to back it off a bit and give that flat part of the rod toward the inside some space so the set screw can get on the flat part and the pinion be meshed correctly?

  13. #13
    phmaximus's Avatar
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    I think with washers the motor will move around a little possible weekening the screws...

    id recomend not driving it until u can get the mesh spot on, because it will cause excessive ware

    but something like these are worth a look,..
    http://www.tamiyausa.com/product/ite...oduct-id=54129

    http://www.rc-race-and-drift-japan.c...oducts_id=3179
    LOSI: 5IVE-T, 8IGHT-E, MICRO SCT
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  14. #14
    EXT2Rob's Avatar
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    WOW! Those motor spacers are a GREAT idea! That should solve the OP's problem!
    Just a schmoe....


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