Model Helicopter Bearings
Bearings need to be looked after to last. The main enemy is dirt and lack of lubrication. Shielded radial bearings offer some protection from the outside elements and these are becoming the standard from most all manufacturers. Still, avoid operating in dusty areas. Thrust bearings are not shielded but their location in the blade grips offers some protection.
Most thrust types have a cup shaped ball retainer (cage) which should face inboard to retain grease better against the centrifugal forces. These should be greased several times throughout the flying season. This maintenance will also help to minimise bearing related radio glitches (metal heads) in addition to increasing their longevity.
Radial bearings should and normally do come pre-lubricated from the bearing supplier with grease. Continuous oiling can wash the grease out through a solvent action. Grease offers a sealing action between the bearing shield and the inner race reducing the ingress of dirt. I like to clean and grease these bearings every year or so. The biggest lubrication problem is the shield. Some are retained with a circular retaining clip and are easy to disassemble, clean and pack with grease. Other shields are swaged in place and can be destroyed upon removal.
These bearings can however be repacked with grease by hand since the clearance between the inner race and the shield is relatively large. No tools are required for this messy job. Grease can be forced in by plugging the inner race with your thumb and forcing the bearing into the palm of the other grease laden hand. It is easy to view the new lubricant oozing out under the other side of the bearing. You will be amazed at the dirt and grime purged from the bearing.
The tiny, sometimes non-shielded bearings on the control levers are best oiled due to the problems encountered in working with something so small. The rotating controls will require more attention here since they are under the most severe use. If you do not like a mess then there are certainly greasing tools available for the model helicopter bearings.
When selecting grease, a silicone type will not dry out as quickly over time like those containing solvents. There are many grease brands and types so read the label before you buy, but don’t skimp and choose quality.
Hidden and forgotten bearings seem to be the most neglected. This might be the case with the tail rotor take off on a shaft driven machine. The support shaft bearings in the boom might one day seize and take out the shaft if ignored for too long. Wet gearboxes will certainly keep their bearings lubricated as long as the grease level is maintained.
The swashplate bearing rarely sees lubrication other than what is spread around from fuel residue. This is easy to grease while the swashplate is removed. Push down and plug the hole in the center ball with your thumb and hand pack as mentioned earlier. You will see clean grease purge between the rotating and non-rotating portions of the swashplate. Be sure to clean all the excess grease with rags or paper towels. After the first flight slight amounts will be slung since the bearing was over filled, so wipe this off and you are done.
When removing bearings they certainly can be damaged, especially if they are hammered out by the inner race. A steady push is preferable using two sockets and a vise. One socket is bigger than the outer race but smaller than the bearing block, the other socket contacts the inner race. A long bolt, nut and washers can also be used to supply the push instead of a vise.
When installing always push on the outer race only. Many bearings are staked into position after installation. A small center punch can be used for this job on the bearing block. Be gentle since it doesn’t take much metal deformation to secure things in place. Fits can be restored between bearings and bearing blocks with loctite bearing retainer. Loctite may also be used in place of bearing staking.
Another type of bearing is available and unique to Boca Bearing, a company supplying bearings to dealers and individuals world wide. This bearing is called an Ultra sealed bearing which offers much more protection from the elements along with superior lubricant retention. It has a teflon back up ring behind the shield to which dirt must circumvent to enter the ball and race area. It is manufactured in miniature sizes and would certainly be most beneficial in exposed areas. Such places in my mind would be mast bearings. Hidden areas like a shaft drive in the tail boom will benefit since one can expect longer life due to the superior lubricant retention.
Boca also stock many rubber sealed bearings as an effective alternative. The cost is reasonable and while I’m not recommending going out and replacing for the sake of replacement, I do suggest you take a close look through attrition. Conventional sealed bearings with/without low torque seals can be found at some local supply houses but they don’t have the selection and stock that Boca has. The Ultra sealed types are recommended by Boca for engine front bearings and in the doubled ended sealed state.
This application relies on the bearings own lubricant and due to double sealing is claimed to prevent fuel leakage and corrosive conditions encountered with shields, which by the way should be open at the back for proper engine oil lubrication. As an added engine benefit, bearing degradation through the ingression of erosive elements is substantial reduced. My personal feeling on the rubber seals is that if you are not concerned with the small additional seal friction you will be rewarded with better sealing.
A true labyrinth seal the Ultra seal is not. Don’t let this discourage you from using the Ultra sealed bearing though, as it is a very good compromise between the shielded and rubber sealed bearings. Typical rpm ratings for greased rubber sealed bearings range from 25,000 for a 60 sized mast bearing up to 36,000 for a tiny 5X11mm bearing which might find application in a clutch stackup. Shielded and ultra sealed types will be rated slightly higher. The point being is that these small bearings are never going to burn up their seals at model helicopter rpms, regardless which ones you choose.
I have talked to Boca and they can supply both metric and standard sizes in the Ultra Sealed version. They are available in metric sizes from 3x7x3 to 12x18x4 and from 1/8″x 1/4″ x 7/64″ to 1/2″ x 3/4″ x 5/32″ in inch sizes, which would cover just about every heli application. Some model helicopter manufacturers sell a bearing block assembly so you can expect to save money by replacing only the bearing. Boca also carry thrust, needle, flanged and auto-rotational one way bearings in addition to various lubricants used in their bearings.
Call tool free at 1-800-332-3256. E-Mail <email@example.com> They are located in Florida, USA.
AST Bearings carry a large variety of miniature bearings in three configurations, shielded, rubber sealed, and a superb low torque rubber sealed type. They don’t have the reference to model applications like Boca, so you must have a size for each individual bearing when ordering. Also include any special design requirements such as a flanged type.
Call toll free at 1-800-526-1250. E-Mail <firstname.lastname@example.org> They are located in New Jersey, USA.