Bad Bearing!
Now go take a time out and think about what you've done!

All right, a show of hands: How many of you have the favorite heli that's worked wonderfully for a long time - in fact, because it's worked so well, you've not had to do much to it? Get a bit sloppy about maintenance? Did you kind of forget about the bearings? Well, I did and it bit me.

My old Gold Futura has been around 8 years now. and over those years it's seen many flights. Most of the time, it's been a very well behaved machine. Of course, it's seen the ground on more than one occasion, but still, it's been put it back together and fly away bird. Never had any odd problems. - up until recently. No, I'm not talking about the four stroke part - I FINALLY have that fixed. What I'm talking about is radio problems - and I never had any radio problems with this heli.

One day when I was fighting and such with the four stroke conversion, I had it on a test table and as I was working with the engine, it suddenly lost radio. Fortunately, it was being held down. The radio came back and I was able to shut it down. I checked all the radio connections, tested all the servos, the switch, looked for possible problems with wires and such and found nothing. Took it back outside, brought it up to hover and the heli seemed fine. It suddenly went on the fritz again, but I got lucky and only cut some grass with the tail rotor. This time I replaced radio parts - switch, receiver and battery.

Being that I was still fighting with the motor, I concentrated more on that aspect of my troubles. I finally got the motor fixed and back in the heli so I took it out to do some hovering. No problems what so ever. Everything was great; the motor worked great and there wasn't a hint of radio problems. I figured that it must have been some sort of interference from the motor. According to YS Performance, one (of many) problem with the motor was that the liner was loose (for the record, THEY had "repaired" it once already!), so maybe that was causing the interference.

I hovered it in my yard enough to satisfy myself that it was going to work, so off to Slim's Flying Field for a bit of 'leg stretching'. In hover, the rotor speed had been fairly low ~1500, my upstairs rotor speed was a bit higher closer to 1650. I brought the bird up into a hover, started adding throttle and then boom - Radio Hit! I got lucky, got the radio back and pulled an ugly auto - minimal damage. Then it dawned on me, I was getting hit every time I throttled up above hover. Craig Golgowski watched this happen and had the same thought. What was it? It had to be a bearing!

A Bearing you say?
Absolutely! Think about it. One of the things we always check on our helis is the bolts and nuts and fasteners, making sure that they stay nice and tight. The vibration in our little machines is pretty intense - A lot of pulses are flowing through the heli each time it takes to the air - the motors run, in general, 16,000 rpm. A pretty high cycle vibration from just the engine. A loose bolt, vibrating around 16,000 times per minute can quickly cause radio interference.

So, think about a bearing. A dry, dirty, neglected bearing. These little jewels usually have seven to nine little itty bitty balls running around between a pair of tracks - the inner and outer races, turning anywhere from 1700 rpm (main shaft) to ~6,000 rpm (tail). Let a bit of dirt get inside and because you've let the bearing go dry and unlubricated, now you have nine little balls running over a speck of dirt 6,000 times a minute. That's 54,000 little vibrations being made per minute. Suppose that this dry, dirty, neglected bearing has also cracked the outer race, because it's tired. Now we have another 54,000 vibrations added per minute. Doesn't take rocket science to realize that you can get some extremely high frequency vibrations going. Say, what? You have TWO dry, dirty, neglected bearings? There's even more vibration being added.

Also, don't forget that our bearings are dry and you now have these little balls not only playing hop scotch with the dirt and the crack in the race, but they are running around between a pair of little tracks (races - two contact points), held in uniform place by a pair of metal bands (cages - two more contact points) while being vibrated by the motor too. Everything adds up against our radio equipment quickly. Oh, the cheaper quality and grade the bearing, the more the parts can move during the vibrations, adding insult to injury. Don't forget the friction cause by being dry too.

These two little dry, dirty, neglected bearings soon decide to revolt against the machine and gang up on the radio equipment. Guess what, you've suddenly lost radio control and helplessly watch your beloved helicopter attack the ground with great authority. Bummer!

How do I know I have a bad bearing?
Go check them! Check them ALL. Everything from bearings in the rotor head to the drive train to the bell cranks. It's pretty easy, it just takes a bit of time. Do them all once a year. Do some of the more stressed bearings such as drive train, tail, and blade grips more often. Eventually, you'll figure out what intervals of inspection each one needs.

Pull the bearing out, put it on a bolt or shaft and spin it. Spin it between your fingers, spin it in the air, just spin it and see what it tells you. They will talk loud and clearly if you listen well.

Does it spin freely or does it seem to have a bit of drag?

Does it spin nice and smoothly or is it a bit notchy?

Does it spin freely, but make noise?

If it has a bit of drag, is it notchy or smooth?

Wiggle the bolt back and forth in the inner race while holding the bearing tight. Does the bearing seem to follow the bolt or is there play?

You want your bearings to spin freely, be smooth, quiet and fairly tight when you check the play between the races.

Some bearings can be saved with a bit of TLC. Others may as well become round filers.
Let's take a quick look:

There are a couple ways to clean your bearings. A can of brake cleaner usually works quite well. Put the bearing on a bolt, aim the little nozzle tube attachment at the inner race at about a 45 degree to the bearing (to make it spin) and fire away with the brake cleaner. If it works right, the bearing should begin to spin pretty freely on the bolt - hopefully, the inner race stays stationary. If you have access to some compressed air, blast it dry. Check the bearing between squirts. If the bearing is clean, it will spin nice, smoothly and freely. It may make a tiny bit of noise, but that will go away with a bit of lubrication.

Suppose that your bearing is now pretty free, but is still a touch notchy. Time to pull the shield! This can be achieved with the end of a #11 exacto knife blade. If you look very closely, you'll see that the majority of the shields are held on with a small circlip. Carefully slip the tip of the blade under the edge of the circlip and it will usually pop right out. Now take the tip of the blade and carefully lift out the shield by inserting it the space between the shield and the inner race. Some of the shields have small tabs on the outer edge - these act like snap rings when pushed down into the outer race. Most of the time these are not removable without damaging them. No big deal, if the bearing is inside something or if you can put the now open side inside what ever it fits in. Do the brake cleaner trick again, this time directly on the exposed balls. Check the bearing again. Most of the time, if the bearing is salvageable, this will be the last resort.

If everything is now smooth, put the shield back on, reinsert the circlip, give it a drop of lube, check for smoothness and put it back in your heli. If it doesn't pass the test, throw it away and replace it with a new one!

The lubrication plays a multi part roll in a bearing's happiness. First, obviously, it lets the bearing work with less friction. This is good for everything. It keeps the metal pieces from actually touching each other - which is the main cause of the interference. Next, it helps by suspending the contaminates instead of letting them get driven into the races or balls. Not that it can't happen, but it's less likely. Also, it acts as a bit of an insulator. The lube actually dampens the vibration movement of the pieces of the bearings. This is a good thing too.

If you have access, a way to clean bearings that works really well is to use an ultrasonic cleaner. These use high frequency vibration to dislodge the contaminates. Quite often, the ultrasonic unit will have a special cleaner that works with it - a bonus!.

If you keep on top of your bearings, usually all they need is a quick cleaning and lubing. They should last for quite some time. If you neglect them, be prepared. It's cheap insurance to replace a suspect bearing with a new one than risk a crash. Even a ten dollar bearing is cheap compared to a hundred buck set of blades.

Oh, one last thing. Set your radio so that the fail safe mode puts the servo to a preset postion, not hold. If the radio interference is a result of a certain speed (as was my case), set it so the throttle goes to a setting that will allow for a slow descent. That way, the motor will slow down, the interference will diminish and you get control back.