What is Slotcar Racing.
By Ray Gardner
Wheelie Car Basics.
by Peter Shreeves
What You Want To Know About Magnets.
By John Sojak, Trik Trax, Inc.
Improve The Handling Of A Slotcar Chassis.
By Ray Gardner
Build and repair a Slotcar Track!
by Ray Gardner with a slight edit by Bob Herrick
Body Painting, Trimming And Mounting Techniques.
By Ray Gardner
An International Affair.
By Dan Green
Last modified: September 29, 2005

| Drag Racing Specialties Home Page |

By Dan Green

  • When asked to write an International 15 motor article, my reaction was full of extremes. My first thought was one of excitement. I'd only been racing a couple of years so I thought this could be a great way to address areas of interest the newer racer might have, especially since it's still new to me. But then I felt a little terrified. I thought to myself: "You write computer programs for a living-not magazine articles. You're just a newbee racer-not a Montague, Koford, DeBella, et al. You're not qualified to write this article. O.K., you got hot a couple of times and got your name in the magazine. But what do you really know about motors? You're just guessing about what's going on inside a motor. You can't see lines of flux (Ricky Werth promised some glasses which would do this, but he never got them done, or so he said. He won the Great Plains Series in Group 27). You're so dumb, you put brush cream on the face of the brush instead of the sides and you're going to tell someone else about motors? Come on now." But then, like a true hard core slot racer trying to make an impossible pass under and around a five car pack, I said "Sure, Teresa, no problem. I'd love to do an article." The little voice in my head just chuckled a dirty little laugh. O.K., so here I am about to tell you everything you have ever wanted to know about International 15 motors. The problem is what to tell. I've tried about every combination of motor configuration I can think of; big gap-big arm, little gap-little arm, little arm-big gap, tall magnets, short magnets, lowered magnets, even four (quad) magnets. Each configuration, when they worked (I try not to remember all the time I spent on those that didn't work), had certain advantages and unfortunately disadvantages. Throughout this discovery and development process I was always struck by a couple of things. First, the motors that worked (and there were some I tried only for information sake knowing they shouldn't work at all but they still did) were similar in that the basic construction was very good. The positioning and alignment of the magnets, brushes and bushings, as the British would say, was "spot on." Second was something Alan Dodson (current Group 27 world record holder and Wichita racer/track owner) had said. He contends "It's all in the combination." Find and use the pieces that work together was the gist of his statement. In my experience I couldn't agree more and that's what I would like to describe here, my favorite International 15 motor combination and how to assemble it to get all possible performance. The design goal of the ultimate 15 motor is to achieve the maximum rpm, at the lightest weight, with enough torque to get through a reasonable amount of glue and still run cool enough to maintain this performance for the entire 3 minutes of each segment in an 8 lane main event. I'm not at all in favor of a box of motors and changing them after racing each color. The opportunity for error in that case is increased and the expense is inappropriate for this class, if not all classes below the "Pro" level. I will try to touch on each of these goals as we proceed through the building of the motor. I think before we get too far though, I'll apologize to any manufacturer I offend by omission. I use parts from all the major manufacturers in my racing program and believe each to have their strengths. But, I feel a meaningful discussion on combinations requires detail specifications. Before we begin building, I'd like to tell you where the magical performance of fast slot car motors comes from, but in my opinion there isn't any magic. Sure, there are a few hot tips of the week that rush around through the slot car rumor/communications network. But the real performance comes from good execution of the basics. Get the basics right and often be surprised how much faster you are than the guy next to you with the latest trick du quir. I see five critical basic areas: Magnets installed square in relation to the arm and precisely across from each other; Brushes aligned to burn in a perfect semicircular cut and exactly 180 degrees apart; Bushings fitted with enough care that they shouldn't need any reaming; Springs with the right amount of tension as dictated by your whole car/track/glue situation; and finally, finding your best combination of parts for your driving.
  • CAN I like to use Koford cans and endbells. Especially, the can with the endbell already attached. Koford does a very neat job of counter sinking the screws and aligning the two pieces. Since the can is a one-piece stamping, it is very rigid. It also is meaty enough to allow for custom cutting. For the beginner I will stress that cutting the can is not a requirement. It constitutes a part of the combination, a trade off of horsepower for handling. However, weight savings is something everyone is interested in and the can is a good place to begin. The field strength of today's magnets do not require as much metal in the can to support the field. Weight removed from the back of the car can strongly enhance cornering performance. One to 1.2 grams can be removed from the can without severely compromising the magnetics. (See photo #1). Do not cut legs of can narrower than 1/8" or loss of torque will result. It is important also to maintain the symmetry of the can so the magnetic field will be just as symmetrical. This will also allow the motor to do a better job of flowing air (i.e., increased cooling, reduced drag on the armature pumping air.)
  • ENDBELL There are essentially only two endbells to choose from, Koford and Mura (Camen's and others being a machined Mura). The Mura endbell is superior in formation and registration of hardware mount points. Its advantage is its strength and perhaps its larger bushing. Its disadvantage is its weight. My preference is the Koford endbell. It is very lightweight yet rigid and the bushing material seems to be harder, therefore lasts longer. Its disadvantage is the ill-formed indexing numbs for the buss bars. We'll come back to the endbell after we install the magnets.
  • MAGNETS (Ed. Note: Magnets used in old 16-D type setups, and often refereed to by a color, i.e. "White," "Red," "Yellow" Dots-meaning the color of paint used to mark them-have been out of production for more than three years and are no longer legal for use. Many advanced International 15 racers still use Front Line series 5000 or 6000 but our understanding is that these too are no longer available. Only shorter length ceramic magnets manufactured today by Camen, Champion, Front Line, Koford, Mura Pro Slot, RJR (and perhaps others) are legal according to the 1992 USRA Rules. While perhaps not as strong (according to gauss meter readings) as the old style, the newer magnets are lighter in weight which translates into increased handling. Now back to Mr. Green.) White dot magnets run very cool and have great horsepower potential but with a great weight penalty. Yellow dots handle very well because of low mass, have a good power curve but tend to run hot. (I understand new engineering is coming from Koford.) Front Line Protech's are my choice as the best of both worlds. They have low mass for good handling, high energy and good field shape for performance and run very cool-i.e. reliability.
  • Choosing the right combination of armature size and air gap will depend on your track configuration and available power. The bigger the armature size the greater the torque. The motor will be snappier and less glue sensitive. The smaller diameter arms will have a smoother power band (less torque) and accelerate to their maximum rpm quicker. Higher track power will allow you to run the magnets closer with less air gap. Running more air gap tends to free the motor up, and allows a little more rpm. If taken too far though, torque goes away and the motor will seem to bog easily. In general I recommend .500" diameter arms in a setup with an air gap of .512" to .518". The installation of the magnets should begin with a trial fit to check for desired air gap. Scrape the paint from inside the can in the area where the magnets will be glued. A small grinding stone in a Dremel works well for this. Also, remove paint from the bushing area. This will save you some time later. Place the magnets into the can. (The magnet marked with black goes to the axle side.) Attempt to insert the air gap tool, also called a "slug" or bushing installation tool. The slug should fit freely with 10 to 15 thousandths "play." This clearance will leave room for the epoxy you'll use to affix the magnets to the can. If there isn't the desired clearance you may wish to sand the back of the magnets. Wet/dry sandpaper in PVC/plastic pipe cut in half makes a great sanding trough. Next, we'll do a trial fit of the armature to determine the lateral position of the magnets. With the magnets in the can, slide an armature in (best not to use a good arm since it might get scratched) and attach the endbell. You are trying to determine where to position the magnets so they will be centered on the armature stack, yet allow the arm to extend into the endbell far enough for the brushes to have adequate contact area on the commutator. This is a very important step. Arms are not all the same length. So, position the magnets so that there will be room for spacers on each end of the shaft. Accomplishing this, mark the outside of the can with a line(s) to indicate the edge(s) of the magnet(s). Now we're ready to glue the magnets in the can. If the magnets/slug/epoxy is going to be a tight fit, skip to the next paragraph. If the magnets aren't so tight, then I recommend you construct a "Dave Jones" C clip made from .055" wire (see photo #2) to hold the magnets in place. (Dave's a long time racer, track owner and my first teacher in the subject of motor building.) Drill a 1/16" hole at centerline of the can behind each magnet attach area. The 'C' clip will apply pressure to the magnets through these holes while the epoxy cures. Make sure the magnets and can are clean. Mix the epoxy. I prefer a steel filled epoxy like J. B. Weld of Devcon. I usually get a little tense and tend to rush after mixing the epoxy. The epoxy allows enough working time to get this step done just right. So, if you're like me, take a deep breath and relax a little. Apply a thin, even coat of epoxy to the inside of the can, covering just the magnet attach area. It's safer, of course, to have a little too much epoxy as opposed to too little. If it gets a little sloppy, don't worry. We'll clean up after a while. Next, apply a thin layer to the back of one magnet and place it into position in the can. Use all caution to keep epoxy off the face of the magnet. Slugs make lousy armatures and don't turn worth a toot when glued to the magnet! Repeat this step for the other magnet. Now is usually when you discover you've put the magnets on the wrong sides. If so, cuss, wash everything with soap and hot water and start over.
  • Next, slip a bushing over the pinion end of the slug's shaft and insert the slug and attach the 'C' clip (if you're using one.) Move the magnets into their approximate positions. Basically, just "sight" them in, align the magnets flush to one end of the slug making them exactly across from each other and with the mark you made on the back of the can. If you can slide the bushing into its hole in the can then you are assured to this point the magnet positioning is in the ball park. Use a Q-tip to remove any excess glue. Install the endbell, being cautious not to glue it. You may need to wash your hands and wipe the can down at this point. Installing the endbell at this time will assure the proper position of the endbell bushing. To dial the magnets into their final position, measure the depth of the magnet from the top and bottom of the can with a steel rule. (See photo #3). Adjust the magnets until the measurement from the top of the can and from the bottom are the same. You can't be too picky about this. Horsepower can be captured or lost right here. (Magic!) Another method you can use, if you have access to dial calipers, is to measure the distance the top face of one magnet is to the top face of the other. Adjust the magnets until the top distance is the same as the bottom distance. (See photo #4). I like this method since calipers give such small, precise readings. It's now ready for the oven. Bake 45 minutes to one hour at 225 degrees. If your wife is like mine and says, "No way...not in MY oven," set it under or on a light bulb. Before we disassemble the can and move to the endbell, let's solder the can bushing in place. Remember, it's already on the slug shaft from the magnet fitting session. I like to stick the endbell end of the slug shaft into a block of wood while I'm doing my can bearing soldering. This will let you turn the can while you hold the iron still. Use lots of acid flux and enough silver solder to fill the gap between the bushing and the hole in the can. Lastly, before disassembly, cut a deep scratch across the top of the can and into the top of the endbell. This mark will allow us to reassemble the motor with all the pieces in their proper positions. Disassemble the can, remove the slug and 'C' clip and give everything a quick soap and hot water bath to remove all the acid flux.
  • ENDBELL ASSEMBLY The next steps will be to epoxy the endbell bushing and buss bars in place. This is necessary, since its possible for the bushing to become loose and spin or the buss bars to shift. You can kiss good performance good-bye in either case. To prepare the endbell, begin by removing the bushing. It's a simple press fit, so use an axle as a punch and it will tap out. Using an X-acto knife, cut several scratches in the endbell bushing landing area. This will give the epoxy something to adhere to and act like small keyways. Next, sand or fill the buss bar attachment areas on the endbell, completely removing the hardware nubs. This will rough up the surface and make for a better bond. I run bodies very low in the rear and find the Koford buss bars are too tall. I usually make an angle cut across the top of the front buss bar and redrill the hole for the shunt wire. (See photo #5) To prepare the endbell bushing for installation, grind or file several scratches on the bushing's outside edge. These will work in conjunction with the scratches we made in the endbell to create a very positive bond. Using a 1/8" or similar drill bit, countersink both sides of the bushing hole to remove the sharp edge. Now sand both sides of the bushing to remove any irregularities. Since the arm spacer may rub against this surface, we don't want any stresses or vibrations introduced by a rough surface. To install the bushing, place it on the comm end of an old armature (now your motor assembly tool) and coat with a very, very small amount of epoxy. (See photo #6) Try to keep epoxy only on the outside edge of the bushing. Keep it from behind the bushing, so the bushing will insert completely into the endbell. Leaving the bushing on the armature, press the bushing into the endbell. Remove the arm and clean any excess epoxy from the bushing with a Q-tip, using extreme care to keep any epoxy from the hole in the bushing. To assure that the bushing is aligned, attach the endbell to the can and insert an armature sized drill blank through the can bushing and into the endbell bushing. The alignment should be such that the drill blank falls through. Adjust the position of the endbell bushing with the drill blank shaft until a perfect alignment results. Next, apply a light film of epoxy to the front buss bar attachment area of the endbell. Avoid the screw holes. Place the front buss bar on the endbell and secure for curing with 0-80 screws. Repeat this process for the rear buss bar. Once again, pop into the oven. If you're ambitious, you can do the magnets and endbell epoxying all in one process. While the endbell is curing you can cut the brush hoods. My preference are Mura hoods. I have had no success with vertical brush hoods. Since the Koford buss bars already have spring perches we can cut them off the Mura's. While you're at it, I like to reduce the overall size of the hood and open the spring path much like you find on Pro-Slot setups. (See photo #6) This will eliminate the possibility of the spring hanging up as the brush wears. Hold the hood firmly with needlenose pliers while doing this. Brass likes to catch and grab Dremel wheels, causing nasty bends. De-burr the finished hood thoroughly. With the endbell installed on the can, attach the spring post "cups" and brush hoods to your endbell with 0-80 screws. I like the Fantom aluminum and Camen Teflon cups. The Fantoms are very nicely formed with a flange at the base which correctly positions the spring. The Camen's are great since they fight heat, a spring's number one enemy! Be cautious not to overtighten the Camen plastic cups. They can flair and bind the spring. Next, do a rough alignment of the hoods. Using a Koford brush alignment tool, adjust the hoods until they seem to be perfectly across from each other and the tool slides freely through them. Now attempt to slide a drill rod/blank through the endbell bushing, alignment tool and can bushing. (See photo #7.) Adjust the hoods until the rod slides freely. Fine tuning the hoods is ultra critical. If getting the magnets in the right position isn't the most important thing in a setup, then I'll promise you the brush positioning is. It's in this step that you can make an armature come alive to its full potential, or, turn a great arm into a "yawner." To do the fine tuning, go through the process of inserting the alignment tool through the hoods again. But this time be so precise that the tool will fall through the hoods under its own weight. Similarly with the drill blank. Adjust the hoods until the rod will fall through the bushings and alignment bar under its own weight. Now, place the setup on a block with the alignment tool still in position. Measure the distance between the block and the bottom of the tool on the front end of the tool and the back end. Adjust the hoods until this measurement is the same for both front and back. The alignment tool in Mura hoods typically is loose. To get an accurate reading you will have to check the lowest point the tool will fall to the highest point it can be raised while maintaining the setup flat against the block. Measure these two extremes at both the front and back and get them the same and you've really got the hoods dialed in. MAGIC? HOT TIP? No, just good basics. It may take several passes through these steps to get it just right, but the time spent will be well worth it.
  • ARMATURE On arms I have no favorites. If it's a good one I use it. If it's real good I save it for the big races. If it's a great arm I save it for qualifying. Pro-Slot arms (were originally on Mura blanks-they now have their own); Camen arms (were originally on PK blanks) and Koford arms are on the X blank. Pro-Slots have a durable hardened shaft, consistent performance, and seem to work the best in my Koford magnet setups. Camen's also have a durable shaft, and with the wider PK stacks provide more opportunity to cut the stacks to smaller diameters. My best main event arms seem to be Camen. Koford arms are lighter and therefore are often very fast. My best qualifying arms are Koford. This means they are usually hoarded and not raced. The unfortunate fact about 15 arms is that they are not all created equal. They all have 50 turns of #29 wire and hopefully the stacks are the same length. But there, the similarity ends. Where they vary in construction and performance characteristics is: blank used, commutator timing, consistency in timing from segment to segment, initial balance, comm roundness, shaft straightness, neatness of winds and perhaps, most importantly, electrical resistance in stacks and consistency of resistance from stack to stack. I'm not offering this as a complaint. These variances are to be expected in a mass-produced, essentially low-profit item-but, rather as a way for you to explain why one arm runs better than another. Knowing these characteristics will help you in your quest for the best combination. What you should find and very importantly, record in a notebook, is a ranking of your arms. Number each of your arms and each setup. After a race, make a brief note about the performance of an arm and setup you ran it in, plus the track and power conditions. In time you will come to the point of having arms ranked and matched to setups for practice/backup motors, weekly races, big races and maybe a real "cherry" one for qualifying. Commutator timing is the measurement of the comm slot position to the center of the stack. Essentially, the comm timing on all slot car armatures is advanced. That is to say, the comm is rotated ahead of the center of the stack in the direction of armature rotation-toward the leading edge of the stack. This measurement is represented in degrees. My timing preference for 15 arms is in the 34 to 38 degree range. This range seems to provide the rpm range and power curve I'm after. But to make these relatively high timings work you have to use the right gear ratio. High timing begets heat if geared with 10 or 11 tooth pinions. It will require 8 or 9 tooth pinions to be effective. The numerically higher gear ratios the 8/9 tooth pinions yield will put less load on the arm. The arm will accelerate faster, run cooler and effectively provide a smooth power transmission which impacts handling and drivability. Gear ratio is another part of the combination. With an 8 or 9 tooth pinion we're going to give up a little top end on top end in order to get it back in the corners and tight sections of the track through increased acceleration and drivability. Plus, we're going to see the motor running just as well at the end of a 3-minute heat as it did in the beginning because of reduced heat. My typical gear ratio depends on the arm and its timing. For moderately advanced arms, 34 to 36 degrees, I will gear 9/38 or 9/39 for a King track. An arm with higher timing or smaller diameter (below .500") I will gear 8/36 to 8/37. O.K. You've selected an arm. Here's how to install it. The first step will be to do a trial fit of the arm in the setup. Oil the bushings lightly and place the arm in the setup and install the endbell. Be cautious with the comm! No scratches please! We'll clean off any fingerprints later. The arm should slide and spin freely in the bushings. If not, use a 2 mm. reamer to align and bore the setup. (See photo #8) I prefer not to ream the bushings at all, but sometimes the endbell does not go back on the can in the exact same relationship that we had when installing the magnets and bushings. This can cause a slight "drag." No binding allowed! If a bind occurs at this point, retrace your assembly steps and correct the problem. A variation in the slug shaft vs. the armature shaft can also cause a very slight drag. You want the shaft-to-bushing clearance to be as close as possible. This will minimize vibration which will improve brush contact and even the gear mesh performance. Also, as a quality control step, examine the air gap around the arm. Hold the setup at eye level with a light shining on the setup from above. Looking at the setup from the pinion end, view the light reflecting from the yellow endbell and notice its shape (See photo #8). If the arm is properly centered in the setup, the air gap between the arm and the magnets will appear uniform and equally shaped on each side. If the arm isn't centered, try repositioning the can bushing to correct the problem.
  • The next step will be the final assembly of the can. Oil the bushings lightly and spin the arm. It will center itself in the magnetic field. Examine the spacing of the arm in the setup. There should be enough room for at least one spacer on each end. Estimate the number of spacers required. Disassemble the can, apply the spacers to the arm and reload the arm into the can and attach the endbell. Repeat this process until the spacing is perfect. You will save time by not screwing the endbell on each time. Just hold it in place with your fingers until the arm has just one spacers width of total endplay. Having done this, prepare the arm and install it for the final time. Pass the end of a tooth pick through each comm slot to remove any foreign material. With great care not to slip, pass the end of a ball point pen along each comm slot to burnish the edges. This will remove any burrs. Now clean the comm with a perfectly clean, lint-free soft rag soaked with lighter fluid. Use great caution to not snag the cloth on the slots. Install the arm in the can and attach the endbell with the screws.
  • BRUSHES, SHUNTS AND SPRINGS I use Camen light springs with no modifications. They are very consistent in pressure from spring to spring and can be reused from rebuild to rebuild. I check the tension when I disassemble the motor. If there is no significant drop and no evidence of corrosion, I'll reuse them. Insulate both ends of the spring. This, in conjunction with the Camen plastic spring posts, will do a very good job of insulating the spring from heat. The cooler we can keep the spring, the more consistent the tension. I like to use Mura Big Foot brushes. (Ed. Note: Almost everyone today uses the newer model Mura Super Big Foot II brushes.) The brushes can also be reused. I always use new brushes for bigger events. But for weekly events, brushes will usually last 2 to 3 races. (I almost always rebuild the motor after every race. More on this later.) Polish all four sides and face of the brush with very fine sandpaper or Crokus cloth. I don't use a break-in tool on the face of the brush. I feel it puts too rough a finish on the face and creates too much arcing at initial break-in. I widen the spring slot in the brush to the width of the shunt wire using a small ignition point file. We'll use the depth of the cut to adjust spring tension so don't cut it too deep yet. I use Trinity braided silver shunts. They are very easy to work with because of their braided construction. They won't fray as easily as stranded shunts and their stiffer body allows them to stay in position during installation. The silver content will assure good contact and conductivity.
  • As the first step in installing the brushes, flush them off with contact cleaner. Any TV contact cleaner will do, the Radio Shack degreaser in the bright red can is a good choice and readily available. Slip the front brush into its hood, attach its spring and check that there is no binding and that the insulator on the short leg clears the brush hood. Now, attach the shunt wire. I bend a 'U' in the end of a length of shunt wire. Place the short end of this 'U' into the brush spring slot and latch the spring down onto it, making sure to get all the strand ends tucked neatly under the spring insulator. The shunt, like the insulator, should cover the entire length of the brush slot for maximum contact, but not interfere with the brush hood. Now, route the shunt to the buss bar; using as little wire as possible but leaving enough slack for the brush to move during wear, also allowing clearance for spring removal and making all this look as neat as possible. (See photo #9) Pass the shunt through the buss bar, wrapping the buss bar eyelet with two turns of the shunt wire. Solder the buss bar end of the shunt in place. Use enough solder to assure good conductivity, but not so much that it will flow too far through the shunt and restrict its necessary movement. Repeat this process for the rear brush. Now let's talk about spring tension. As we said earlier, this is one of several basic areas of importance that will have significant impact on allowing performance to happen. We often think of brushes in the sense of friction. It would seem logical then, that less spring tension would mean less friction and therefore greater performance. This it true to a point but it can work just the opposite. Less spring tension can increase arcing. Arcing creates heat. Head reduces spring tension. Less spring tension increases arcing and the cycle can continue until, in the worst case, the motor slows down or fails. It is important to address reducing friction, but a certain amount of spring tension must be maintained to provide the optimum conductivity between brush and commutator. So, the question becomes, how much spring tension is needed? The answer will depend upon your cars inherent drag-friction in the gears, at rear axle bushings, the wind load of the body, etc.- the track configuration and available power, since these are the ingredients that will constitute the load (i.e. heat range) to which the motor will be subjected. You want enough tension for the motor to be as fast at the end of the 3-minute segment as it was at the beginning, but no more than that. Any more will result in a lose of potential performance. And since heat will reduce spring tension, we'll have to actually load the spring with a little more tension than we actually need, since we're setting the tension while the motor is cold. Having said all that, I'll try to be more specific. First, you must have a fiddle stick. They are made by Sonic. If properly cared for, they'll last forever. It will allow you to take spring tension readings. Without these readings you will only be guessing. Your fiddle stick will not necessarily give you the same reading as mine. No two fiddle sticks are exactly the same. But in general I set my spring tension in the 3 to 4 range. Experimentation is the only way to find your number. Lower the tension until the motor starts getting hot, then raise it back up. It will be very helpful to check your fiddle stick against someone else's and compare notes on what tension is working the best. The catch is, you'll both have to check the tension in the same way or you'll be comparing apples to oranges. I check the tension just above the spring perch by pushing the spring until it just moves, reading the stick as I lower the spring back down to the perch. I feel this method gives very consistent readings since we're reading the spring in its natural position. New Mura brushes, Camen light springs and shunts usually have a little too much tension. I lower the tension by deepening the slot in the brush. Make a small cut and take another reading, repeating this process until the tension is just at your perfect number. Remember to flush the brush with cleaner before inserting it into the hood. Fingerprints and grit simply won't help performance. On a rebuild, or for qualifying with higher power, you may need more tension. Use thicker insulators for a small change or open the spring up for a bigger change. Camen lights are typically at the 4 to 5 o'clock position (small leg on the 12, long leg between 4 and 5.) You can pull the long leg back toward the 5 or 6 position with your fingers and it will stay there. I prefer not to do this and I definitely don't like to put bends in the springs. I am concerned this will fatigue or stress the spring and adversely effect its performance or even cause it to fail under heat.
  • BREAK-IN Breaking in the motor on a power supply will allow the brushes to become fully seated while minimizing the arcing, plus give you a chance to evaluate the motor before you take it to the track. The Slick 7 is ideal but the cost may be prohibitive. (Ed. Note: Koford also now offers these.) A 12-volt auto battery and controller will work. I used an auto battery charger and 3 ohm wire wound ceramic rheostat for a very long time. It provides adequate current when an 18 volt 20,000+ microfarad capacitor are attached in parallel, plus it had an amp meter. Lightly oil the bushings and run the motor at 3 to 5 volts for about twenty minutes, or, until there is a uniform twinkling along the trailing edge of the brushes. This will indicate they are fully seated. If you are able to monitor the amperage you will notice it to be initially high, then gradually come down as the brushes become fully seated, then rise slightly and stabilize in the range of 1.5 to 2.5 amps. The amp reading alone will not tell you if the motor is good. If the amps are high and the motor runs hot, there may be a problem with spring tension, binding in the bushings, or bad components. It's normal for the motor rpm's to fluctuate initially. The brushes are being ground by the comm and the grit being thrown out will momentarily disrupt the continuity of the brushes. The rpm should stabilize or continue to increase after a minute or two. Should the motor continue to "stutter," consider bad brushes or a contaminated comm. I like to hold the motor in my fingers for the first few minutes. This gives me a chance to monitor the heat and vibration. Vibration will occur from running the motor too slowly, and a higher rpm may get past the vibration. Be careful not to over-rev, too little oil in the bushings, worn bushings, or an inadequate balance or bent shaft. At the track run the motor at one half to three quarters speed on a lane without any glue until it warms up. After Warm-Up, take it up to race speed and evaluate the motor responsiveness and gearing. The only way to do this right is by using the lap timer. I simply don't trust my eye or ear to always tell me the truth and I know the lap timer doesn't lie. I'm not suggesting that you ignore your instincts. I'm just stressing that you must use accurate data in your evaluation. If you are using a brand new arm it may shift during this practice session. Shifting is the changing of the arm as a result of heat and stresses of motion. Windings may slightly reposition. The comm may change shape slightly. Initial shift is to be expected and shifting usually occurs only once. Don't run the motor after the arm shifts. Disassemble the motor and send the arm off for reconditioning-a comm cut and re-balance.
  • MAINTENANCE Well, you won the race, the motor ran fast and cool, and its time to do the first tear down. I usually run an arm for practice and a full 8-lane race before I send it in for reconditioning. I feel this a good practice and keeps my horsepower in top form. But it is definitely not a requirement to change arms that often. A good arm and setup will perform well for 2 or 3 races without any problem. The problem I have, which requires fresh horsepower even for weekly races is Jay Horn and Larry Jones. They finished 2nd and 4th respectively at the NAT'S, while Bozo me worked in their pits. The first step in the tear down is to re-fiddle stick the springs. If the tension is still good, use them again. Next, remove the brushes and check the wear pattern. The brushes should have a perfect, semicircular cut. Adjust the brush hoods to correct for any deviation. When you are confident with the brush hood position, solder them to the buss bars. This will keep them from shifting. If the brushes still have sufficient length to keep proper spring tension, and are not completely oil soaked, use them again for 2 or 3 weekly races. Next, check the bushings for side to side play. Grab the shaft with your fingers-it's a good practice to not cut arm shafts too short-and try to move the shaft from side to side. A very slight movement is O.K., but it doesn't take much before I replace them.
  • CONCLUSION As I was writing this, I realized how much information and how many points there are to make, just about the motor. And, very importantly I know where so much of the information I have came from. It was the Wichita racers who have always been so good to spread it around and help each other out. It's people like Jim Hollabaugh at DJ's Raceway who have promoted and keep USRA racing going here. I can only wish that all of you have it as good as we do here. Challenge everyone and the manufacturers to keep passing the information around and helping the newer racers. Doing so we will be assured of always having racers and friends to share our fun.
  • Best of Racing. Sincerely, Dan Green
  • (One final Ed. Note: While this information is tailored to high-end, group racing aficionados, any owner and any serious racer should know how to do these procedures. The care and deliberation Dan Green has taken in making his International 15 motors "winners" can be applied from the least expensive stock 16-D all the way up through open motors. Bob Cozine and thousands of the better racers across the country have been doing their motors and set-ups this way for years. Couple that knowledge, care and deliberation with driving skill, honed through years of practice and you have an almost unbeatable combination. Good luck in your own development of both!)