Installing and removing pinions

Model Airplane News, Jul 1999 by Gimlick, Greg

WE RECENTLY DISCUSSED a wide array of topics dealing with power systems, including how speed controls work, how motors are made and why they work, and how to properly time motors for specific applications. Now it's time to look at why we might change timing and adapt motors to new applications. You may want to change your direct-drive motor to be geared, or you may prefer to add a larger prop to enhance performance. Whatever the case, it's not hard to do, but there are right and wrong ways to do it.

Whether you use a gear drive or a belt drive, you'll need to install a pinion gear or pulley on the motor. With a gear drive, you'll also need to change the motor's direction so the prop will turn in the right direction; with a belt drive, the direction will remain the same. If you add a gearbox, go ahead and reverse the motor and make the necessary timing adjustments before you proceed. If you plan to do a project with a can motor and don't want to go through the reversal and timing exercises, it's worth investigating the Kyosho* Magnetic Mayhem reverse motor, as it already turns in the right direction for a gear drive.

GEAR TALK

At the risk of oversimplifying things, let me first explain that in a normal gearbox, there are two gears: the pinion, which fits on the motor shaft, and the spur gear, which is the large gear on the prop shaft inside the gearbox. There are exceptions, like planetary boxes and some titanium boxes, but the one thing they all have in common is that the motor must have a pinion gear. That's my purpose in this column: to describe how to properly install and remove pinion gears.

With any job, there are good ways and bad ways to do it; some folks might get away with doing it the "wrong" way, but that doesn't make it right. We've all done "field-expedient" repairs, but let's concentrate on methods we would use at home in the comfort of our shops. Proper equipment makes the job much easier but, in a pinch, you can install a pinion using a bench vise (preferably with a drill press).

I prefer to use a tool that's specifically designed to install pinion gears; I think you'll find that it is money well spent. The tool I use was designed by All Up Last Down champion John McCollough and is distributed by New Creations R/Ct for less than $30. On its pinion end, this tool has a plate in a normal gearbox with holes that accommodate a wide range of motors and let you see your progress. At the other end is a concave socket-head bolt that automatically centers the motor shaft as you place it in the motor. The outer threaded rods allow the end plates to be adjusted to fit every motor I've come across, and you can adjust the socket-head bolt to work with a lot of motors without having to adjust the outer plates. When everything is lined up, you only have to turn the socket bolt with an Allen wrench until the pinion is where you want it. One of the beauties of this tool is that you can also carry it in your field box for easy fixes.

I mentioned before that you could also do the job with a bench vise and drill press. In the photos, I am installing a pinion in a standard Graupner* Speed 600 motor using my drill press and machinist's vise. My vise has "soft jaws" that are replaceable face surfaces that are softer than most metals and won't damage a brass pinion gear. If you look closely at the rear of the motor, you can see that it is placed in the vise so that the jaw presses directly against the rear of the motor shaft and misses the two terminals. The front of the motor shaft is placed in the pinion and then carefully aligned with the V-groove in the soft jaw of the vise. This is absolutely critical to avoid bending the motor shaft when you apply pressure, so take extra care to ensure proper alignment.

If you don't have a vise with soft jaws, protect the gear with some hardwood blocks. After you've pressed the gear onto the motor shaft, the end of the shaft will stick out, so it helps to drill a small hole in the hardwood blocks to accept the shaft. By using a vise with a V-groove, I can see how far I've pressed the gear onto the shaft.

For better results, use a drill press, too. I mount the vise on my drill press and square it up properly to the drill, then I chuck the motor shaft into the drill and lower it onto the pinion, which is placed over a clearance groove in the vise top. I then use the drill press as a bushing press to lightly push the shaft through the pinion gear. To check your progress, simply return the drill to the raised position.

EVERYONE HAS AN SO"PINION

Now that you have the pinion on the motor, what if you decide to change ratios or gearboxes? What if you pushed the pinion too far onto the shaft?

Pinion removal tools are inexpensive and easy to find, and they're available for motor shafts of various sizes. Simply slide the tool around the motor shaft and hold the gear while the bolt presses the shaft out of the pinion.

A while ago, I picked up a pinionremoval tool for less than $12 at a hobby shop that caters to the R/C car crowd. The problem with this particular version was the way it rested against the bottom of the pinion gear. It's a steel ring and harder than the brass pinions, so if I had tried to remove a tight pinion, I might have damaged the edge of the teeth where they rested against the curved sides of the puller. Now I use a tool that's available for various shaft sizes from New Creations R/C. You can buy a combination set that will handle the smaller shaft sizes and another set for big motors (up to 1/4-inch shafts). This tool is a bit more expensive, but if you do any number of pinion changes, it will pay for itself in the long run-especially because it won't damage the motors.