This article was originally published in RC Driver’s June 2015 issue.
Protect your teeth from abuse
Words By Scott Donaldson
The driveline of an RC car or truck is truly a work of art. Whether you’re dealing with the mesh of a clutch bell or pinion gear and spur or a ring and pinion gear inside a transmission casing, your vehicle’s gears are all about transferring power as efficiently as possible while withstanding the strain placed upon them. Setting your mesh incor- rectly can, at worst, damage your gears, at best cause your gears to wear out prematurely or cause excess drag. We’re going to show you some quick tips on how to properly set the gear mesh between your pinion/clutch bell and spur and between the ring and pinion gear inside your gearbox.
Proper size Allen wrench (5/64-in., 2.0mm or 2.5mm) or #1 Phillips screwdriver for motor screws.
0.050-in., 1/16-in. or 1.5mm Allen wrench for pinion set screws
Nitro or Gasoline-powered:
2.5mm or 3mm Allen wrench
To set your electric motor’s gear mesh, screw in your motor screws to the point that they’ll hold the motor in place while you can still swing it toward or away from the spur gear. Once these screws are installed, attach the pinion to the output shaft of the motor. Check to make sure the pinion gear is centered on the face of the spur gear, adjusting the location in or out as needed. Once everything is centered up, tighten the pinion set screw down. Now it is time to set the gear mesh itself.
Slide the motor toward the spur gear until the gears begin to mesh with each other. You need to slide the motor and pinion toward the spur, rocking the spur gear to ensure that there’s some backlash between the gears. Some is good, more, not-so-much. You’ll want to have just a slight amount of movement between the pinion and spur to ensure the motion is not bound up. Once you’re happy with the gap, tighten the motor screws down com- pletely. Before you reinstall the gear cover, rotate the spur gear by quarter rotations to verify that the gear mesh is set to accom- modate a spur gear that isn’t perfectly round.
If you’re having problems getting the gap set properly there’s an age-old tip to ensure proper gear mesh each and every time. You can insert a piece of standard notebook paper between the pinion and spur gear before you slide the motor into place, squeezing the paper between the pinion and spur gear. Tighten the motor screws down, pull the paper out and you should have a perfect gear mesh each and every time.
While there are a lot of similarities between setting the mesh on a clutch bell and spur gear and pinion and spur there are some basic differences. Unlike an electric car or truck, an engine mount will generally be bolted to the main chassis with four screws. As such you have to really make sure things don’t shift when tightening everything down. You can use the same tech- nique here as with electric cars, even down to using the paper technique to set the depth of the gear mesh. There are two things you need to do as you bolt everything into place. The first is to use a small amount of thread locking compound on the screws that hold the engine mounts in place. These vehicles see a lot more vibration and abuse than their electric counter- parts which can cause the engine mount screws to back out. Thread lock will help prevent this. The second is to use a cross- pattern when tightening the screws, just like you would on your full-size car’s tires. This ensures that everything mounts squarely.
Setting the mesh between the ring and pinion gears inside your gearboxes on a 4WD SCT or 1/8-scale buggy or truggy can dramatically extend the life of your gears. There are two ways to adjust this mesh, both at the ring gear and at the pinion gear, but the method of setting this mesh is similar. You’ll use a variety of shims to set the depth of the pinion gear compared to the ring gear. By adding shims between the pinion gear and the bearing that supports it inside the gearbox you’ll be moving the pinion gear closer to the ring gear for more tooth engagement. Removing shims here will reduce the tooth engagement which could actually improve efficiency slightly. Likewise you can also change the position of the ring gear in relation to the pinion gear. Adding or removing shims between the ring-side of the diff and the support bearing will move the ring gear closer or further away from the pinion gear.
IMPORTANT DO’S AND DON’TS
• If your pinion gear set screw loosens up or is stripped replace it immediately.
• Less is more when it comes to thread locking compound.
• Don’t mix gears of different pitch, this doesn’t end well.
• You can extend the life of your ring and pinion gears by coating the gears lightly with Team Losi Racing Great Grease or Tamiya Anti-Wear Grease.
• Pinions and clutch bells wear out. When they do they can damage the spur gear too. When in doubt swap it out.
Setting your gear mesh is super-easy once you know what you’re doing. It will extend the life of your gears and help you get more power and speed out of your car or truck. The more you pay attention to the details, the better your overall experience will be in the long run.