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  1. #1
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    Spur gear stripping

    I noticed the other day while I was putting my new rpm arms on my tmaxx 3.3 that it looks like my spur gear is starting to get striped. I thought maybe the motor mount was loose or something but it wasn't. Anyone have any suggestions or know what may be causing this? Or even if there is a upgraded spur gear? Thanks in advance!!

  2. #2
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    youll want to stick with the stock plastic spur gear.... check your gear mesh, to loose or to tight will strip them, also its possible your mesh is ok you just landed hard while holding the throttle...

    end result replace it with a stock spur...
    Traxxas is good, but so are other Manus

  3. #3
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    not unless your going to go to steel spur gear.then you must go to harden steel clutch bell.then if you have plastic gears in the tranny with a steel spur you could end up wrecking those.so i would stay away from steel its costly.just replace your pads and gear and set the gear mesh with a piece of paper and you will be fine.

  4. #4
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    The reasons for a spur stripping are; 1: incorrect mesh 2: engine and trans. misaligned 3: bent or broken chassis 4: broken driveline part causing it to bind up 5: getting your tires in a bind while the throttle is nailed 6: getting a lot of traction while at wot and the tires spinning fast. Like when landing from a jump, or running wot over very bumpy terrain. They make steel spurs, but then you'll need hardened steel clutch bell, hardened steel transmission gears, steel drive shafts, alum. axel carriers, super strong diff., alum wheel hex's and now I need alum wheels. The best thing to do is just get another $3 plastic spur and make sure everything else is good. Get one with a couple more teeth, it will give you more power and be easier on the gears.

  5. #5
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    Excellent information guys! CRITTER90 One thing you will ALWAYS find here at the Traxxas Forums are a lot of very knowledgeable and experienced guys that are always willing to help. I feel sure that if you will just follow their lead you will solve your problem quickly.

    If you ever decide you want to take the gear mesh a step farther, buy you both a new pinion and spur. Before installing them put an index mark on each that you can line back up anytime you have them un-coupled. Due to manufacturing tolerances there are no two teeth identical on any gear. Take you a carbide file or an emery board like Mom uses for her fingernails and de-burr both sided of each and every tooth on both gears taking care not to change the profile of the teeth. You will very likely see low spots in the teeth and that’s OK, what you are concerned about are the high spots. That’s what creates excess noise, robs you of horsepower, forces you to run your mesh looser than optimum, and not to mention adds to cogging issues.

    Once you are satisfied with the gears, install them with the index marks lined up. I balance my gears before installing but, that’s optional.

    I want to stress at this point………ANYTIME you have the pinion far enough away from the spur that they become un-meshed, LINE UP your index marks and every tooth will be back running against the one it was mated to.

    Now that you have the gears re-installed and indexed, close up your mesh. Your motor magnets will probably not allow you to check the mesh between every tooth for a complete revolution but slowly advance the spur gear in the normal direction of rotation, rock it back and forth and check the backlash until you find the point where the backlash is greatest and put a temporary reference mark at this location. I have been around RC for 25 years and have never seen a spur gear that was either concentric or hub-centric but you CAN minimize the run-out. I ruined several spur gears learning to do what I am going to suggest next so I want to say I AM IN NO WAY RESPONSIBLE if you do not achieve the expected results! Turn the spur gear to the low spot that you marked earlier (low spot on spur gear = greatest backlash). Don’t jam the pinion up against the spur but close the backlash up to zero at this point and tighten motor screws. Turn the spur gear one complete revolution at this time and you will notice when you get to the side that was high the backlash will be really tight at that point. This is where it gets really tricky.

    At this point you need a source of heat. I use a Weller WPA2 Butane Soldering Iron with a small hot-air tip which allows me to concentrate the heat in a very small area (to keep from melting things). With the car running at 3 mph or so (on a stand) in reverse I start to heat the spur gear while listening to the pitch of the gears. When the spur gear gets hot enough you will notice the gear noise change. Remove the heat and let the car continue to run until the spur cools. You can use a heat gun on COOL, a hair dryer on COLD, a fan, or compressed air to speed up the cool down process.

    Once the spur has cooled to room temperature, repeat the process with the car running in the normal or forward direction.

    Let it cool and set your backlash to .003-.004 or, (as some say “just a tick” of slack). Make one more revolution of the spur to check the final results.

    This process (if done correctly) will minimize the radial and lateral run-out in the spur gear allowing you to run a little less backlash, while decreasing amp draw and gear noise.

    REMEMBER…….. RE-INDEXING will put the same teeth back together EVERY time, keeping your backlash (or mesh) more consistent, while minimizing new wear across the teeth and increase the life of your gears.

  6. #6
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    I'm not sure that I understand exactly what your saying about the teeth on the pinion always hitting the same teeth on the spur. I have a gear ratio of 2.25:1, which means that the pinion rotates 2 and 1/8 times per revolution of the spur. Which means that the pinion will have to spin 16 times to get back where it started. Causing every tooth on the pinion to touch every tooth on the spur a little over 7 times. The only way I can think of to get the teeth to always hit in the same place, is to have an even ratio of 2:1. That way every rotation of the pinion would always be on the same side of the spur per rotation of the pinion.

  7. #7
    Marshal Double G's Avatar
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    Quote Originally Posted by Mark Ball View Post
    ... a gear ratio of 2.25:1, which means that the pinion rotates 2 and 1/8 times per revolution of the spur.
    Psst. It will be 2 1/4.
    The Super Derecho

  8. #8
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    Oops, I do that all the time. I guess it would only be 8 revolutions and 3 1/2 times.

  9. #9
    RC Turnbuckle Jr. Wildman4910's Avatar
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    Indexing does you no good depending on the CB/SG ratio, as not all will be non~hunting & line up again, on a hunting CB/SG the marks will not line up again.
    Look out for the tree/crunch!

    LiPo? Naw NITRO!!

  10. #10
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    i'll spend $3 any day vs filing, indexing, aligning, heating, cooling, balancing .................

  11. #11
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    Thanks guys for the detailed information. What is my mesh tho? I'm still a rookie lol

  12. #12
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    The "mesh" is how tight or loose the clutch bell meets the spur gear. You want to have as much surface contact as possible between teeth as they push against each other. But still loose enough that there is the smallest amount of play when holding one gear and wiggling the other one. It should spin freely if you spin the spur backwards, no tightness. Most people say to set it so a piece of paper can be run through the gears and not cut into the paper but still crinkle it. I stripped a few spurs with that method before I figured out the perfect gap on the mesh.

  13. #13
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    It says make sure not to over tighten the spur gear. How tight is tight? Because mine came loose and I don't know how tight to get it.

  14. #14
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    Quote Originally Posted by HICKFARM View Post
    It says make sure not to over tighten the spur gear. How tight is tight? Because mine came loose and I don't know how tight to get it.
    Snug it down. Don't reaf on it or you will break the trans input shaft. Once it's snug, back it off about 1.4 turn.
    Scott

    4909 MAXX 3.3
    4910 MAXX 2.5

  15. #15
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    If you tighten it too much, it will warp the clutch disk. Just use thread locker and snug it down.
    Last edited by Double G; 05-25-2013 at 12:50 PM.

  16. #16
    Marshal Double G's Avatar
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    If you have the Revo style slipper you will have the spur gear then two spring washers that look like this: () then the nut. Don't flatten them. I lock the input shaft and then tighten the nut to the point that it puts nice indents in my thumb when is spin the spur gear trying to make it slip.
    If it has slipped too much you may have glazed the pads. Take some fine grit sand paper put the slipper pads (still attached to the clutch) and with even pressure sand them down.
    The Super Derecho

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