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Motor Tuning Secrets - Stock Motor Tuning

The stock motor shown in this article is a Trinity blue endbell paradox motor, which is often used in stock races as a handout motor. This motor is very similar to a Paradox or P2k motor. It does not come with brushes or springs. Keep in mind that the tuning tips mentioned in this article will apply to nearly every stock motor, not just the blue endbell motors.

The first step in the tuning process is to disassemble the motor. On every stock motor, there are two screws that lag the plastic endbell to a metal ring located in the motor can. By removing those two screws, you can remove the endbell and tear the motor down. In the pictures, these two screws also hold a small tab. The tab will be used as a point to solder capacitors to once the motor is built, so don't lose the small tabs. Once you have the endbell off of the motor, you can remove the armature from the can. The arm will have a plastic like disk and a few small metal shims. The plastic like disk is for keeping oil off the comm. The metal shims are for spacing the armature within the magnetic field of the motor can's magnets. Sit the shims and plastic like disk off to the side for now. Note: The shims may stick to the can and endbell when you remove the arm. Carefully flick the shims out with your finger or small tool. Don't lose the shims.

The next step is to remove the bushings from the motor. I like to remove the bushings, so I can polish them really well. I polish the surface where the armature shims ride and I polish the hole when the armature shaft spins inside. It is possible to polish the bushings without removing them from the motor, but I have found that I can do a better job if I remove them from the motor. I use a few light taps from a hammer onto a small steel hole punch. Be careful, since it is easy to smack dents into the bushings.

With any luck, you can usually push the endbell bushing out without using a hammer. You will need to gently tap the steel punch a few times with a hammer to force the bushing out of the motor can. Remember, lots of very light taps will be far better than one massive thunk. You do not want to dent the bushing, so be careful.

Equate toothpaste is the best thing I have found so far for breaking in bushings. Cheap toothpaste acts as a light abrasive that can break in the bushings without damaging them, and the toothpaste is easy to rinse off with nothing more than warm water. I've tried other break in products, such as Trinity Bushing Buster, and products like that often remove too much material from the bushing and stay on the bushing even after a good cleaning. If you break in the bushings too much, then the armature will wobble as the motor runs and then the brushes will bounce. The key to proper bushing break in is to get the bushing hole very well polished without increasing the diameter of the hole. Toothpaste seems to work perfect for this task. Simply place a shaft (can be as simple as using an old armature) into a dremel. Then coat the end of the shaft of the cheap toothpaste. Drop the bushings onto the shaft, and then run dremel on high for several minutes. Add more toothpaste to the shaft as needed. Then clean the bushing really well with warm water.

The surface of the bushing where the armature shim rides is not 100% smooth. For lowest possible friction, we need to sand the surface of the bushing with 2000 grit sandpaper until it feels as smooth as glass. Then clean the bushing with Buggy Blast. Sit the sanded bushing by the bushing you have not sanded yet. Compare the surface of the sanded bushing (left) with that of a stock bushing (right). The bushing on the left is noticeably smoother than the bushing on the right. Do the same steps for the other bushing.

The comm on the armature may look smooth and perfectly round, but it will nearly never be until you cut it yourself. Even "Pro tuned" motors have out of round comms, so it is a good idea to cut the comm no matter what kind of stock motor you are tuning. The first step when cutting the comm is to spin the armature and coat the comm with your sharpie marker. The ink from the sharpie marker will show us where the comm needs cut. 

Do a light cut using the comm lathe. Then stop the lathe and look closely at the comm. Most likely, you will see some spots where the sharpie marker ink was not removed. These are the low spots on the comm. Keep taking light cuts of the comm with the lathe until there is no more sharpie marker ink left on the comm. At that point, you will know that the comm is perfectly round.

Now that the comm is perfectly round, we will want to make sure the slots between the comm segments are ready to go. Clean the debris out using an exacto knife. Be very careful and very gentle when cleaning the slots. Then run the tip of a ballpoint pen down the slot. Do not press hard. All you want to do is slightly round the edges down. The amount of rounding does not even need to be visible to the naked eye.

Spray some Buggy Blast onto a paper towel. Lightly rub the comm with the dampened towel. This will collect the ink and metal that is still on the comm. Remember, clean is fast. Any gunk left behind is just slowing you down.

Chuck the armature into a dremel. Spin the arm while rubbing the shaft in 2000 grit sandpaper. Check the paper frequently. Move to a different spot on the paper once a dark spot forms. Get the shaft as smooth as possible. Do this for both ends of the armature.

Now that the shaft is sanded smooth, we need to polish the surface. Use Blue Magic Metal Polish to polish the shaft. The polish will remove a dark layer of grime and tarnish from the shaft. Do this for both ends of the armature. Once you have completed this step, the shaft will feel as smooth as glass. 

We are about to start putting the motor back together. Hose the arm down really well with Buggy Blast, and then with compressed air. Make sure it is perfectly clean, because clean is fast. Then place the plastic like disk onto the comm end of the arm, and then drop one metal shim onto each end of the armature. Place a drop of bushing oil or Tribo into each bushing. Then slide a bushing onto each end of the arm, with the smooth side of the bushings facing the shims.

Drop the arm and bushing assembly into the can. Place the endbell back onto the can, with the endbell's alignment tab aligned with the can's notch. Lightly press the entire assembly together. Then lightly tap the assembly the rest of the way together with a hammer. Remember that lot of light taps is far better than one giant thunk. You do not want to dent the bushings or bend the armature shaft after investing so much time into this motor. So be very careful and very gentle when tapping the motor back together. Once it is tapped into place, you can screw the endbell screws back into the motor to hold the endbell in place. 

Now that the motor is assembled, we need to make sure it spins very freely. If all of the steps have been followed properly, the arm should spin nearly as well as bearings. To check how it spins, I install a pinion on the shaft. It is easier for me to grab the pinion and give it a spin than it is to try to spin the bare shaft. If the shaft does not spin freely, tap the shaft on the table a few times to try to reseat the bushings. Sometimes bushings don't go in perfectly straight, and that can cause some binding. Table tapping the shaft on both ends can usually correct that problem.

Once you are satisfied with how freely the arm spins, it is time to shim the arm properly within the motor can's magnetic field. To do this, I start by removing the silver colored metal shims. Then I reassemble the motor. I place the pinion on the shaft and give the arm a spin. Then I pull the pinion to see how much play it has in one direction. Then I spin it again, and check play in the other direction. Install shims as needed to soak up the proper amount of play. In most cases, I end up using a thim brass colored shim and a teflon shim on each end, with the teflon shim riding on the bushing. However, this will vary from motor to motor depending on how the arm centers in the magnetic field. I stock up on metal and teflon shims of various sizes to accommodate all of the possible shimming possibilities.

Once you are satisfied with the shimming of the armature, it is time to make sure the endbell is aligned properly. Stock motors have a locked timing of 24 degrees. However, there is generally about 1 degree of play in the locked timing notch and tab. The notch in the can is often slightly too wide for the notch, so you can wiggle the endbell around a little bit. Loosen the endbell screws and wiggle the endbell to see if there is play in your stock motor's locked timing notch and tab. To advance the timing as much as you can within this amount of play, move the endbell's tab to right as shown in the picture. Not all stock motors will have play in this area, but this is worth checking on every stock motor you build since it is free power. Once you have the endbell aligned properly, tighten the endbell screws so the endbell does not wiggle around anymore.

At this point in the building process, the motor is back together. We are now going to move on to the brushes. The hoods that hold the brushes are usually not aligned properly, and there is enough play inside the hoods to allow the brushes to get cocked a few degrees when the motor is running. Our goal is to make sure the brushes are aligned perfectly straight across from each other and each brush is wearing in the exact center of the brush. The only way to make sure the brushes are lined up properly is to put brushes in the motor, run the motor, and then check the wear mark on each brush. I like to use a pair of Reedy 766 brushes that I have ground flat with a file as my alignment brushes. Don't use those copper shunt cheapie brushes that come with non-Pro Trinity motors, because those brushes are actually slightly wider than most race brushes. The width of the brush is one factor in how much the brush will cock inside the hood while running.

If the wear mark is in the exact center of each brush, then the hoods are aligned properly. If the wear mark is not in the exact center of the brush, then that hood is slightly misaligned and needs to be realigned. If the hoods are even slightly misaligned, you need to realign them. Do not stop until the alignment is perfect and the brushes wear in the center when the motor is running. Even a slight misalignment can cost you 10% of the potential power of the motor, so don't give up during this step. Also, you need to actually run the motor to create the wear mark. Do not just spin it with a dremel or drill or by hand. Always spin the motor by applying voltage to the motor. I usually use about 3 volts when I spin my motors to check hood alignment.

These two pictures illustrate the brush cocking issue more clearly. When a motor is running, the spinning comm causes the brush to get pulled into a cocked angle like the picture on the left. Even though the hood is aligned straight, the brush is getting cocked inside the hood. I have exaggerated the amount of brush cocking in the picture to make it clear what is going on. Even getting cocked a millimeter can send the timing off a few degrees. The picture on the right shows the brush perfectly aligned with the comm. Keep in mind that the hood will often need to be cocked slightly to ensure the brush is lined up perfectly when the motor is running.

To align a hood, you need to loosen the spring post and the screw that hold the hood. The spring post is a 4.3mm nut. Trinity used to sell a tool for the spring post, but does not sell it anymore. You can usually get by with a 4.5mm tool. I had to file down the outside of my 4.5mm tool so it would fit between the endbell's heatsink and the spring post. You may need to do the same. The screw is just a standard phillips screw. You can use an alignment bar to hold the hood during alignment, so it is easy to hold the hood in place while you tighten the screw and spring post back down. Remember, you need to align one hood at a time. Do not use one of those tools that aligns the hoods directly across from each other, because we want the brushes (not the brush hoods) to be directly across from one another. The hoods will actually need to be cocked slightly to counter act the brush cocking inside the hoods. Also, make sure you do not bend the hoods. A bent hood will often bind up the brush, and the last thing you want during a race is to end up with a stuck brush. If you cannot cock the hood enough, remove the screw and elongate the hole a little bit with an exacto knife. You will not need to remove much material. In most cases, a half a millimeter is plenty. But what ever you do, do not stop realigning the hoods until both sides have a perfectly centered wear mark.

Now that the hoods are aligned, your motor is readr for the brushes you plan to run in it. You can choose pretty much any laydown brush you want, and you'll have a solid running motor. The tips supplied in this article will impact the performance far more than the brush choice. Certain brush combos will make a few more watts than other brush combos, while other combos will tend to place less wear on the comm. For club racing, nothing beats the Reedy 766 brushes. These brushes make really good power, yet can be raced several times without any noticable wear. For a few more RPM, try a Reedy 767 brush, an E-brush (Trinity 4499), a cross cut E-brush (Trinity 4504) or a Trinity 4503. Those three are harder than the 766, and will add noticeable wear to the comm. A good compromise is to run a 767 or 4504 on the positive and a 766 on the negative. For top levels of competition, install the 4503 on both the positive and negative, and then recut the comm after every run. In most blue endbell motors that I have tuned, the 4503 brushes will yield about two watts more power than the 766 brushes. At the club level, you'll never notice two watts, so stick with the 766 brushes at the club level. With 766 brushes, I usually recut the comm every six to eight runs. As for springs, I usually use a pair of red Trinity springs. When I tune the motor on the dyno, I adjust spring tension as needed. In nearly every case, a motor will run best with a pair of reds or a red/green combo. Some guys prefer to start with a red spring on the positive and a green one on the negative, and tune from there.

Solder the brush shunts to the endbell. Be careful, because solder can very quickly wick up into the shunt. When that happens the shunt becomes very stiff. A stiff shunt can cause the brush to get hung during a race. While you have your soldering iron hot, you should also solder capacitors to the motor if the motor needs them. Some motors have capacitors preinstalled into the endbell. For example, the Trinity P2k, P2k2, GM3, and Monster Stock all come with preinstalled capacitors.

Place the motor in a break in stand. Make sure there is plenty of oil on the bushings. Run the motor for 30 seconds at 3 volts with no fan attached. During the first 30 seconds of brush breakin, it is extremely important that the motor has no load on it. Then attach a fan, and run the motor at 3 volts for an additional 300-500 seconds. Then check the face of the brushes for wear. You want the brushes to have a wear mark that extends to all four corners of the brush face. If the wear mark is only covering some of the brush face, you need to break the motor in for an additional 300 seconds. Continue checking the brush wear and breaking in until the brushes are completely broken in.

Certain brushes place a lot of wear on the comm during break-in. If the comm is noticeably chewed up after break-in, you will need to do another light cut on the comm. After doing a light cut on the comm, you will need to do an additional 30 second break-in to reseat the brushes.

Congratulations, your motor is ready to race. Clean it up with some Buggy Blast and compressed air, and then add more oil to the bushings. Then you can either throw it into your car or your motor bag.


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