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How To Remove & Install Plastic Wheels & Gears

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  • How To Remove & Install Plastic Wheels & Gears

    This is best way I have found to remove and install plastic wheels and crown gears from knurled or solid axles with minimal damage.

    Make a drawing of the axle assembly and mark down the distances from the inside of the wheel hub, of the wheel that isn’t being removed, to the crown gear, and to the wheel hub of the wheel that is being removed. Also indicate which way the gear teeth are facing on the crown gear.

    The most important thing not to do, is put any load on the wheel rim, all the loads have to be on the wheel hub.

    An adjustable wrench is mounted in the vise with the opening set to the axle size. (photo # 1)

    The axle is gripped with a pair of Vise Grips next to the crown gear, between the wheel that is not being removed.
    Insert the side of the axle, next to the wheel being removed, into the slot of the adjustable wrench.
    Tape the wheel to the wrench to keep it from flying away.
    Hold the Vise Grips firmly in one hand, making sure the axle is perpendicular to the wrench, then strike the Vise Grips with a hammer, driving the axle out of the wheel. (photo # 2)

    Set the axle in the wrench on the crown gear and drive the axle through the gear until there is a short piece of axle still showing. (photo # 3)

    Grab the axle with the Vise Grips below the adjustable wrench and drive the axle out of the crown gear by hitting the Vise Grips with the hammer. (photo # 4)

    Make sure the axle bearings are installed in their proper places before pressing on either the crown gear or wheel.

    Start the new crown gear on the shaft by hand, noting the direction of the teeth.
    Place a spacer on the outside of the wheel hub and press the crown gear onto the axle until the axle is almost through the crown gear. (photo # 5)

    Place a tubing spacer against the crown gear and continue pressing the crown gear onto the shaft. (photo # 6)

    Place a longer tubing spacer against the crown gear and continue pressing the crown gear onto the shaft until the crown gear is at the proper distance from the wheel hub. (photo # 7)

    I had to use two different length tubing spacers against the crown gear because my vise wouldn’t open far enough to start with the long spacer.

    Place a small spacer on the outside of the other wheel hub and start the wheel on the axle by hand.
    If the wheel fit is loose, apply a drop of Super Glue on the axle knurl, then press the wheel on until the correct dimension between the wheel hubs is reached.(photo #8)

    Dave
    Last edited by davejr; 09-08-2008, 05:57 AM.

  • #2
    The # 2 photo is a little confusing with the tape covering the wheel.
    This photo should help. (photo # 9)

    Dave

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    • #3
      Well thought out, and presented, thanks.

      Have also read of (and tried) immersing the wheel in hot water. It seems to help.

      Mc

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      • #4
        Has anybody tried putting the wheel/axle combo in the freezer? The metal should contract more than the plastic, possibly until the wheel is a loose fit.

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        • #5
          Originally posted by ElSecundo View Post
          Has anybody tried putting the wheel/axle combo in the freezer? The metal should contract more than the plastic, possibly until the wheel is a loose fit.
          Probably a whole lot less messy that the water thing.

          Mc

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          • #6
            I haven't tried that, but the contraction of the axle across its diameter would be small. And, the plastic wheel hub could become very brittle at sub-freezing temperature.

            Iron based alloys (like mild steel) contract 11.7 microinches per inch, per degree centigrade. A microinch is one millionth of an inch. If the temperature drops from room temperature to 20 degrees F (freezer temperature?) or, say, 20 degrees C to -10C, for a net drop of 30 degrees C, a steel axle is contracting 30(11.7)=351 microinches per inch. If the diameter is .09375 inches, the contraction would be .09375(351)=32.9 microinches, or .00003". I don't think that will be sufficient to ease the wheel off the axle, particularly if you have knurls.

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            • #7
              Yeah, it's obvious when you think about it.

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              • #8
                I'd also be concerned about the plastic becoming brittle, but you also have to consider how deep the knurling is. How many microinches could that be? Every little bit helps when the tolerance is so close that you're relying on slight compression of the plastic to hold the wheel on.

                I have a little story about steel expansion/contraction that may make you reconsider -- measurements be d***ed.

                At the Ninco World Cup Qualifier in Baltimore last year, I went to the finals when my car survived all the qualifying heats while running with a spur gear that was spinning on the axle slightly. It slowed the car down a lot (over a second a lap), but it kept the nose from popping out of the slot, and I could drive the car very hard.

                After the axle had a chance to cool off a bit before the final, when the final started, the car sat on the starting line while the axle spun in place. It had cooled enough to contract, barely making contact with the spur gear.

                That's just the cooling effect from running temp to stationary temp, and I'd guess the difference is less than 25 degrees C, like the difference between the freezer and room temperature.

                So, worth a try?

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                • #9
                  Elsecundo, I dont know what rate a plastic hub whould shrink when chilled, but I gotta believe a solid steel axle would be more dimensionally stable than a plastic hub with a crossection of 2mm or so

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                  • #10
                    Put the axle assembly in a container of alcohol and put it in the freezer, this will lower the temperature another 20° F.

                    The wheel will probably crack when the axle is driven out because it will be brittle.

                    Dave

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                    • #11
                      Interesting story about the spinning gear, Kurt. I am thinking it had more to do with the heated plastic glazing over as it cooled, releasing its viscous grip on the axle, than it did the contraction of the axle. Usually, a plastic press-on part exerts static pressure, exploiting the elastic nature of plastics. The interference (the amount the hole is undersized, to achieve a press fit) would be a couple of thousandths of an inch, so axle contraction of way less than a thousandth wouldn't do much to relieve the pressure.

                      I am also reminded of a spinning, soldered, brass pinion that let go as I coasted over a finish line a few years ago. It let go gradually in the last coupe of laps, so I got across the finish line (in first place) but could drive no more than a foot further, as the motor revved helplessly.

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                      • #12
                        An axle spinning inside a plastic gear heats the plastic adjacent to the hole.

                        The plastic distorts and the hole is enlarged.

                        The gear will keep driving the car at a reduced rate because the plastic gear is soft and sticking to the axle.

                        When the assembly cools off, the hole in the gear gets brittle and the diameter gets larger than normal because the heat has distorted the hole.

                        Dave

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                        • #13
                          This should be titled...

                          ...Remove Plastic Wheels and Gears.

                          Step 1:
                          Remove plastic wheels, plastic gears, plastic bushings and cheap axle.
                          Step 2:
                          Throw them away.
                          Step 3:
                          Replace with aluminum wheels, set screw mounted gear, brass bushings and steel axle.
                          Step 3:
                          Race.

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                          • #14
                            Originally posted by Robert Livingston View Post
                            Interesting story about the spinning gear, Kurt. I am thinking it had more to do with the heated plastic glazing over as it cooled, releasing its viscous grip on the axle, than it did the contraction of the axle. Usually, a plastic press-on part exerts static pressure, exploiting the elastic nature of plastics. The interference (the amount the hole is undersized, to achieve a press fit) would be a couple of thousandths of an inch, so axle contraction of way less than a thousandth wouldn't do much to relieve the pressure.

                            I am also reminded of a spinning, soldered, brass pinion that let go as I coasted over a finish line a few years ago. It let go gradually in the last coupe of laps, so I got across the finish line (in first place) but could drive no more than a foot further, as the motor revved helplessly.
                            Originally posted by davejr View Post
                            An axle spinning inside a plastic gear heats the plastic adjacent to the hole.

                            The plastic distorts and the hole is enlarged.

                            The gear will keep driving the car at a reduced rate because the plastic gear is soft and sticking to the axle.

                            When the assembly cools off, the hole in the gear gets brittle and the diameter gets larger than normal because the heat has distorted the hole.

                            Dave
                            Wrong assumption, guys. We're talking about Ninco ProRace anglewinder gears -- metal-to-metal contact, no plastic.

                            Comment


                            • #15
                              Well...

                              Originally posted by Kurt
                              "Wrong assumption, guys. We're talking about Ninco ProRace anglewinder gears - metal-to-metal contact, no plastic."
                              Voodoo, perhaps...?

                              Cheers!
                              BigDog

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