Ball Bearings By James Goss      It is a well-known fact that if you want your model engine to produce high speeds, you get a ball bearing engine. With some manufactures a ball bearing engine only cost a few dollars more than an engine with bushings. Sleeve bearings are fine for small sport planes, but if you are looking for power it requires ball bearings for that crankshaft to rotate on. With sleeve bearings (bushings) there is just too much surface area making contact between the two metals, the shaft and the sleeve. This contact creates friction and friction places a load on the shaft, preventing the shaft from turning as fast as it would with a bearing of less friction. If you have read my article “Getting to Know Your Electric Starter” I described how bushings are built and some facts about them. Bushings do have some advantages over ball bearings other than costing less. First of all they will not rust like steel ball bearings will. The second and most important advantage is that they will not come apart and destroy your engine. Other than these two disadvantages ball bearings are great for our model engines.         When a bushing wears out it will allow the shaft to move up and down as the shaft rotates. This creates vibrations, noise, and more wear on the sleeve. To test the bushing, simply hold the engine in your hand and try to move the shaft up and down. The shaft should be tight and not flop around as you try to move it. If it has excess movement the bushing is probably bad. Bushings are very easy to replace in your engine. The bushing should be pressed into the housing and not on the shaft. This way the shaft is free to turn and the sleeve is locked in place by the housing of the engine.      When a ball bearing starts to go bad, you can usually feel it as you rotate the engine. It will have rough places as the engine is rotated. Sometimes the bearing may not be to the point of you being able to feel the bad places; instead it will make a strange noise at a certain rpm. If you think your engine is developing a bearing problem, do not run that engine until you check it. If you continue to run an engine that has a defective bearing, the bearing may come apart and destroy the engine. When a ball bearing dissects and comes apart, small pieces of metal from the bearing may be transmitted throughout the engine, digging into the crankcase and scoring the cylinder liner and piston. It could mean the end of your engine unless you catch it soon enough. Replacing a ball bearing in your engine is not hard to do. Always replace both bearings at the same time; never just replace one of the bearings. If you do replace only one, you may be going back into the engine to replace the other bearing in the future.      It does help to have an arbor press to press the bearings into the case or to press them out of the case. If you are pressing the bearing into the case, be sure to always press by using the bearing's outer ring. If you are pressing the bearing on a shaft, be sure to always press it on by using the inside ring. If you don't follow these rules you may damage the bearing by putting too much pressure on the ball assembly, I know because I have damaged my share of bearings. I always use a metal pipe that will fit the rings, either inside or outside ring, to press fit the bearing. If you don't have an arbor press you can still do a good job by using a hammer to tap the pipe while the pipe is on the inside or outside race of the bearing. Make sure the pipe you are using to press the bearing on has a square cut end. The best way to make sure it is square is to cut it with a pipe cutter. If you cut it with a hacksaw the blade will pull to one side and it will not be square. If you do press it on with an out of square pipe the bearing may get damaged, especially if you are pressing it on with the outer ring.      Ball bearings have a bearing number on the side of the bearing that tells you which bearing to replace it with. For example, a large bearing such as the 6204 has some important information in its number. Most manufacturers of bearings will use the last two numbers, the 04 in this case, to specify the diameter of the bearings center hole. Most all bearings today will be metric in size. The 6204 bearing will fit a 20 mm ( ¾ inch) shaft. Simply multiply the last two numbers by 5mm. 04 x 5 =20                            It's not hard at all to remove the old bearings if they are still intact. Remove the piston and press the shaft out of the block, this removes the front bearing. The rear bearing may still be in the housing. A lot of times you will find the rear ball bearing broken apart. The outer ring, balls, and separator assembly have completely been removed from the inside ring. They are just wondering around inside the crankcase and can do some real damage if the engine is run or even rotated by hand at this time. The separator is used to keep the balls from touching each other and it is not a sturdy built device to begin with. With the bearing broken apart there is nothing to press against to remove the bearing. How are you going to get the outer bearing ring out of its case? I only know of one good way to accomplish this task. Place the engine housing in your wife's oven and bring it up to 350 degrees. After about 10 minutes at this temperature, take the engine out and hit it on a solid surface. The ring should fall out from the housing. If the ring does not come out, bring the temperature up to 375 degrees and try again. When you reach the right temperature the aluminum housing will expand more than the steel bearing, this will allow the outer ring to fall out of its housing. Don't worry about the aluminum melting, aluminum melts at 1130 degrees F. Your oven might have a slight caster oil smell for a while but it will fade away soon. Even if the scent doesn't go away, you know how you like to smell the engine exhaust on a cool day, just think what it will do for your barbecued chicken.      I have found a better way to heat an engine to remove the bearing. An induction-bearing heater will do a really nice job and is the neatest way to heat your engine. It only takes a few minutes to get the engine hot enough for the bearing to fall out and I am sure that your wife will really like this technique.  The heater is nothing more than a coil of wire wound on a laminated core with part of the core being removable. It is very similar to a growler, an electrical device used to check an armature in a dc motor. It is called a growler because when you lay the armature into its jaws for testing with a hacksaw blade, it makes a loud growling sound. The induction-bearing heater also makes a growling sound while it is heating the bearing. The removable part of the core is placed through the bearing ring and engine housing. The removable core is then replaced on the main core and the coil is connected to 120 volts. The coil will pull about 18 amps and develops an extremely strong magnetic field that circulates through the core. This magnetic field will induce eddy currents into the steel bearing and aluminum case. Heat develops quickly and it is just as effective as the oven for heating the engine. This is a nice way to heat the engine and you can use a temperature sensor with your electronic voltmeter to keep up with the temperature. This induction heater is not the same as the oven, if you leave it energized with the engine in place, you will have a meltdown. Be sure you are not wearing an electronic watch while operating this device. While testing the bearing heater at work the other day I forgot about my watch. The next thing I knew it was time to go home, I had only been at work for 30 minutes. I have been using this technique every day since then.  If any one is interested in building a device such as this just let me know and I will give you a diagram and specs for its construction.      Have you ever wondered how the steel balls in a ball bearing are manufactured? You may find that it is not unusual for people dealing with ball bearings to not know how the balls are built. Just ask then and see what some strange answers you will get. How are the balls in a ball bearing built? I have had this question ask several times over the years. The other day when we were coming back from the swap meet at Huntsville in Gene's van, this question arose again. I could not think of the steps involved in building these balls to save my soul. I guess this is a sign of getting old. They say that the memory is the second thing to go; I forget what the first is. Since then I have had a memory update by reviewing some of my old teaching notes and here are the five steps for manufacturing the little balls used in ball bearings: Step one: Heading; heading is the process of cutting wire into short lengths called slugs. The slugs are then pressed into a blank, this gives them a spherical shape. It is a round ball at this time but it has ridge marks left on it by the forming dies. So the basic shape of the ball is obtained by pressing a short piece of steel into a round form. For small balls this is done cold and the metal is not heated. For balls over 1 1/8 inch, they are heated first and then pressed into the mold. Step Two: To remove the ridge lines (also known as flash lines), the balls roll between two heavy cast iron plates. The two plates are rotating in opposite directions and are parallel to the floor. Thousands of balls roll between these two plates at the same time. Of course all the balls in between the two large plates are the same size. They can't mix ball sizes during this operation.  This is called Deflashing and the balls come out with no ridge lines and are called Flashed balls. At this time they are round and smooth. Step Three: The balls are now heat treaded for hardness. Thousands of these little steel balls are placed into a giant oven and brought up to the correct temperature. The rate of cooling is controlled for the desired hardness. Step Four: Hard Grinding is a slow meticulous process for proper sizing and sphericity of the balls. It is achieved by using two large metal grinding wheels, horizontal to the floor, and rotating in opposite directions like the Deflashing wheels. Thousands of balls are in this grinding machine at the same time. The balls are brought within .0001 inch tolerances. Step Five: The balls are now finished to have a very smooth surface by lapping them. This is done in a vat that contains thousands of steel balls and an abrasive medium. This is called barreling and is achieved by tumbling the balls in a barrel for long periods of time.      I checked with several manufactures and they all seem to do it about the same way. So maybe this takes some of the mystery out of how the balls in a ball bearing are produced. Most of the time when a bearing goes bad it will be due to one of the balls wearing and becoming out of round. Once a ball develops a flat spot it may damage the race or separator plate. This is when the bearing starts to disassemble itself if we force it to keep working under a load. So take care of your bearings by not running the engine too lean. Remember that even though the bearing is sealed it still gets oil from the fuel for lubrication.