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Noisy / Rough Gears??

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  • Noisy / Rough Gears??

    Seasons Greetings All!

    I've been tinkering around with a couple of SCX cars, and the common feature I'm finding is noisy gears.

    Is this a common trend? And what treatment has worked for you?

    I'm considering toothpaste or extra cut car polish - but I'm open to hearing from others' expriences...

    Thanks & Cheers, Tony.

  • #2
    Valve lapping compound...

    Or just bin the rear axle and get bits...


    • #3

      Simichrome polish works at slow speed, but watch the gear slowly, they are molded warped on the axle. No known cure for that.


      • #4
        ear plugs


        • #5
          If the gear is warped then the cigarette lighter trick could work. Hold the chassis upside down and apply power to the braids and heat to the crown....not too much heat though.


          • #6
            Originally posted by JCZPT View Post
            Simichrome polish works at slow speed, but watch the gear slowly, they are molded warped on the axle. No known cure for that.

            Maybe these two extracts from my old tuning article will help with your problem:

            6. Aligning the Drive Train Back To Index

            a. Now to the rear wheels/tires on the inline drive train. On these drive trains the self aligning crown gear takes a lot of the slop out of the axle. However, on most models it may be beneficial to add washers or spacers between the axle bushings and the wheel to take up any extra slack. This will reduce drive train noise dramatically and make the gears mesh better. When you are satisfied with this setup and have finished any gear selection work you can accomplish wheel assembly gluing (step5d). I also add a small drop of super glue to the crown gear to axle joint to reinforce this joint. Be careful that the glue doesn't wick back into the axle bushings. Also a dab of silicone or white Moly grease on the gear self align slot will reduce friction. One note of caution here: It is usually better to remove and replace inline axle assemblies with the motor removed first because of the possibility of damaging the plastic crown gear. If you do choose to remove and replace the axle assembly with the motor installed be extremely careful that the pinion gear teeth don't damage the crown teeth.

            b. On sidewinder drive cars washers should be added to first, to provide clearance between the pinion gear and the tire on that side, second, to keep the spur gear from rubbing on the chassis cut-out, third, to take up the slack in the axle assembly and fourth,to get the maximum track width that will still fit under the body. This may sound complex but it can be done quite easily using thin washers and first centering the spur gear in the chassis cut-out using a washer between the spur gear and the axle bushing then adding thin washers to get proper wheel clearance on the spur gear side of the axle (check for body to wheel clearance and track width at this time also). After this wheel is set up, add washers to the other side of the axle to take up the overall slack and to position the opposite wheel assembly in the proper place. When you are satisfied with this setup and have finished any gear selection work you can accomplish wheel assembly gluing (step5d). I also add a small drop of super glue to the spur gear to axle joint to reinforce this joint. Again, be careful that the glue doesn't wick into the axle bushings. One mod to the chassis on cars such as FLY sidewinders that you might want to consider here is to cut out the spur slot in the chassis so that gear/axle assemblies may be removed without removing the pod first. This can save time and wear and tear during gear - axle changes. On cars such as the FLY Classic Porsches the motor pod is not hard mounted to the rest of the chassis. On these models it is important that this pod is mounted squarely so that the wheels are aligned correctly.

            c. One problem that many people complain about is gear noise usually on inline drivetrains. This can be caused by several factors and may be different sounds which we will try to explain.

            1.) The first type of noise is a ticking sound that varies with speed. This is usually caused by a plastic gear that has one or more small burrs on the gear teeth. If you slowly rotate the axle you can usually feel the place where the binding is occurring and if you take a magnifying glass under strong light you will see the burr. You can usually correct this problem by taking a very sharp x-acto knife and shaving off the burr. The main cause of these burrs is not being careful when removing the motor or rear axle. The metal pinion acts like a knife and cuts into the soft plastic of the crown or spur gear.

            2.) The second noise is a constant thrashing sound that may be caused by several things. If you are using Slotit pinions they are usually noisy in this way because of their design to get different amounts of teeth into the same diameter gear. You may also get this noise if the mesh is too tight. Sometimes new gears are noisy because they haven't seated themselves. In the case of the Slotits and the new gears you can add some paint rubbing compound to the gears and run them at low speed, being careful to cover the rest of the chassis so you don't create a mess (I use a small plastic bag and rubber band). This will slightly polish the gears and make them mesh better. Afterwards make sure you remove all the residue with water and or alcohol. You can also use an abrasive dental tooth paste instead of automobile rubbing compound. Make sure it's abrasive or else the only thing that you'll get is a car that smells good. In the case of the too tight a mesh you simply need to loosen it up.

            3.) Some crown gears of some manufacturers do not work with other brands because the diameter of the pinion alignment trough is too great. This will cause binding and noise in the gear area. Unless you want to spend an hour sanding down the trough edges just replace the gear with one that fits.

            4.) Another gear problem which can cause quite a bit of gear noise is a problem with mass produced motors. Many times there is a large amount of motor shaft forward / aft movement (slop) because of inadequate armature spacing between the motor bearings and the armature. This can come from production this way or may be caused by the improper installation / removal of pinion gears shifting the interference fit armature spacer found inside most stock motors. In any event, since most of us would rather not mess around the inside of these cheap motors, there is an easy way to take up this slack and reduce the pinion gears "in / out movement" when the motor is accelerating / decelerating. Take some armature spacers (made by companies like Slick 7, Koford, Mura, etc.) or a piece of .078"/2mm ID brass tubing and place enough between the pinion and the motor shaft bearing on the pinion end of the motor to remove all but a paper's width of movement when the pinion is pressed on. This should make a noticeable change in the amount of gear noise especially on inline drive trains. This mod assumes that the slop you remove isn't so much that it causes problems with the commutator /motor brush interface. If this is the case then the only fix is to take the motor apart and redo the spacer set up. This is covered in the REPAIRS section of this article. .

            5.) Periodically you may run into a plastic crown gear that's warped. This can be seen by observing the gear turning at low speed. You can usually un-warp plastic gears somewhat by applying heat to the back side as it's turning at slow/medium speed. the non-tip part of a soldering iron held against the gear will work if you don't have an adjustable heat source.

            6.) Finally, tightening up the slop in the gear/ axle train will probably do more than anything else to reduce rear end noise so follow the procedures for that first and the rest of this may be unnecessary. If you’re using replacement wheel / axle / gear setups, first set the wheel spacing before setting the gear. Once all the slop is removed from the wheel / bearings the gear can be adjusted using a thin piece of paper between the pinion and the crown gear, pushing them together with the paper in between and then tightening the crown gear holding screw. On sidewinder setups this tolerance is built into the motor adapter and is generally not adjustable except in modified setups such as those identified in the race tuning section of the article.


            Car Noise

            5. Excessive noise

            a. Car noise needs to be isolated to the offending parts before a good solution can be found. What should be done first is to figure out if it's a chassis, body, or chassis to body problem. Running the car without the body should quickly identify this fact.

            b. Chassis without the body should be pretty quiet so any racket without the body is either gear, bushing (both axle and pinion shaft; as applicable), motor/mount, gear mesh, front guide or front axle assembly. Removing the front wheel assemblies) and running the chassis will eliminate or identify this area as the problem. Rear axle and pinion shaft bearings should be glued into their carriers. All slop should be removed from the rear axle assembly by using washers/spacers as required. Motor and motor mounts where applicable should be glued in; I like RTV because it is a vibration suppressant and can be removed easily if a motor change is required. Guide slop can be corrected per the info in the General Section. Gear noise can be corrected or reduced after axle shimming by putting a dab of paint rubbing compound onto the gears and running them at low speed for a couple of minutes, stopping periodically to work the compound back into the gears. This should be cleaned thoroughly afterwards with water and alcohol.

            c. On the body first take it and shake it thoroughly to see if any parts are loose (See Body section). Prime offenders on FLY cars are the headlight assemblies which are hot melt mounted and sometimes the weld is not good. Super glue will quickly fix this problem or any other loose parts problem. Be careful to use the glue sparingly because it has a tendency to run and you don't want to mess up that beautiful paint finish with it.

            d. Finally put the chassis and body back together and check for any interference between the gears, motor or wheels/tires and the body. Any interference can be corrected either by shims or by grinding away part of the body underside that is causing the problem. With all that done your car should be nice and quiet. If it isn't than the last thing you can do is add some sound deadening foam between the body and motor (just a small piece should do it) to isolate the motor from the body.



            • #7
              Hi All,

              Thanks for your suggestions and advice - after a combination of a lot of these enhancements, things are much quieter and smoother!

              Cheers, Tony.