Grease Is the Word

Maintenance matters.

4

The squeaky wheel gets the grease, but it is better if everything that needs it gets the proper grease before it begins to squeak. If you consistently use the correct lubricant for your airplane’s various parts, you will go a long way toward preventing problems that could leave you stranded.

While Experimental airplane owners may use any grease they like, greases made for aircraft work better. Just as you won’t find the best aviation hardware at your favorite home-improvement store, you won’t find the best grease for your airplane at the auto parts store. It’s not that automotive greases aren’t suitable. They are simply designed to meet different needs.

These are the three most popular AeroShell greases, all of which are widely available. AeroShell 22 seems to be the most popular choice among aviation manufacturers.

For this article, we will focus on aviation greases available in tubes to fit the standard grease gun. This covers the vast majority of greases that the owner of an Experimental aircraft would likely consider. We also look at the places where they are best suited.

Making the Grease

Different types of grease are formulated to provide better performance in specific situations. Since different users have different needs, we get a variety of greases tailored to those needs. Helicopter main and tail rotors see different kinds of loads than light-plane wheel bearings. Airliner wheel bearings see higher loads than those on light planes. Amphibious floatplane wheel bearings need a high degree of corrosion resistance. Thus, there is no one grease best for everything.

Grease is mostly oil, either mineral or synthetic. Oil makes up 80 to 95% of grease. The rest is thickening agents and performance-enhancing additives. Thickening agents can include calcium, clay or lithium. Calcium is a popular thickener for mineral-based greases, with lithium being more common among synthetics. Thickeners are there primarily to provide mechanical stability and resist water washout. Performance additives may be included to increase corrosion resistance, wear resistance or resistance to high pressures.

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After you have thoroughly cleaned each bearing, be sure to inspect the race for any pitting or corrosion (left). Replace any bearings that don’t look good—before they fail. After you clean and inspect the bearings, be sure to push new grease all the way into the rollers (right). Keep pushing the bearing into the grease in the palm of your hand until it comes through the top side. Work your way around the bearing until it is completely packed.

Wheel Bearings

Unless your airplane is on straight floats or skis, you will have wheel bearings to maintain. If your plane lives on wheels, you will need a general-purpose grease such as AeroShell 5 or 6—both economical and widely available. AeroShell 22 is a good synthetic grease that will match or exceed the performance of AeroShell 5 and work over a wider temperature range. Mobil 28 is a fine choice if you prefer a synthetic grease, but is slightly more expensive and not as widely available.

If you spend a lot of time in wet conditions or, if you have amphibious floats that have wheel bearings under water much of the time, you will want to lean toward AeroShell 22—this is a product that carries the specific endorsement of Wipaire, Inc., maker of Wipline floats. AeroShell 5 is a good choice if you can’t find AeroShell 22, but avoid AeroShell 14 and 33 for wet environments.

Wheel bearings are typically serviced at the time of the yearly condition inspection, but hard use or extreme wet conditions may dictate a shorter service interval. Remember that when servicing wheel bearings, they need to be clean before you repack them. Pushing out the old grease with new grease does not ensure that the wheel bearing is free of contamination. The effectiveness of any grease will be compromised by contamination, so no cutting corners here.

The actual greasing process can be messy and tedious, but it isn’t too bad once you get the hang of it. Take a glob of grease, about two tablespoons, in one hand and grasp the bearing cone in the other with the narrow end facing up. Place your thumb on top of the bearing and press it repeatedly into the grease until it begins to squirt up through the rollers. Then rotate the bearing and do another section until you have completely gone around the bearing. While you are at it, apply a thin coat of grease to the race. It is a little easier to say than to do, but you will get good at it with practice. Low-cost bearing packers have not worked well for me and higher-priced ones are just not worth it for once-a-year use. The hand method has the advantages of being well-proven and cheap. A pair of disposable nitrile gloves makes the job less messy.

In all cases when servicing wheel bearings, be mindful of safety, both when jacking up your airplane and when using flammable solvents for cleaning.

Scott and similar tailwheels should be serviced every year or every 100 hours. This is done with a convenient grease fitting located on the top of the tailwheel assembly.

Tailwheels

Tailwheels should be greased annually or every 100 hours if you are fortunate enough to fly that much. To grease a tailwheel, first make sure the grease fitting is clean. Any dirt or debris on the fitting can end up on the bearing surfaces and cause damage. If possible, cover the grease fitting with a protective plastic cap. Attach the grease gun to the clean fitting and pump in a few squirts of grease. Keep an eye on the grease seal to ensure you do not push it out of place with too much grease. As soon as you notice any movement, stop pumping. Be sure to use a grease that is recommended by the tailwheel manufacturer. Some tailwheels use sealed wheel bearings, so they obviously do not need to be greased, but the pivot joint will still need servicing.

Propellers

Typically, constant-speed propellers are serviced once a year at the time of the condition inspection. If you fly more than 100 hours per year, you should consider servicing the prop every 100 hours. Be sure to consult the prop manufacturer’s maintenance guidelines for greasing recommendations.

Hartzell traditionally asked you to remove the trailing-edge grease fittings on each blade and pump grease into the leading-edge grease fittings until grease squirted out the trailing-edge holes. However, after an enthusiastic mechanic pumped two full tubes of grease into a King Air prop, waiting for grease to come out the other side, they changed their recommendations. They now say to pump not more than one ounce of grease—about five squirts—and call it good. Excess grease can get into places where it doesn’t belong, leading to removal and teardown of the prop in question.

The grease fittings on this Hartzell prop have plastic covers to keep them clean between servicing (left). Ideally, all grease fittings should have these caps. Service your Hartzell propeller at the time of your condition inspection. Be careful not to put in too much grease as per Hartzell’s most recent service bulletin (right). Also, be sure not to mix greases from one time to the next.

Propeller manufacturers all assemble their propellers with grease that they think will sufficiently lubricate and protect their products. They want you to service their props with the same grease and not mix greases. In the past, they gave you some choices. That does not mean you could choose to use any approved grease at any time. It means pick one and stick with it. Mixing greases, especially mineral and synthetic, is not allowed.

As of January 2020, Hartzell assembled their props with NYCO GN 3058 grease, and they expect you to service any prop made after that date with that grease. It is not yet widely available, but Ottosen Prop and Hartzell will sell it to you. Hopefully, other vendors will offer it soon. Propellers made before this year can continue using the grease they have been using. Do not switch to NYCO grease if you are currently using some other grease. Needless to say, if you have a constant-speed prop made by another manufacturer, you should consult them for the most current recommendation on products and procedures for greasing your prop.

If you are currently using a factory-approved grease in your constant-speed prop, it makes good sense to use the same grease for everything else in your plane. That way, you don’t accidentally put the wrong grease in your prop. As an alternative, you can have a dedicated grease gun for prop maintenance and use whatever you like for other things.

Other Applications

What grease you should use for any particular application will depend on the conditions under which it will operate. Choose a grease that best fits the requirements. For example, AeroShell 5 and 22 are particularly good in hot environments, whereas 7, 22 and 33 are the best in extremely cold situations. Among the AeroShell choices, AeroShell 5 and 22 are best in wet conditions. Helicopter mechanics widely use AeroShell 14 for its superior anti-fretting properties. With the information available on the internet, it is pretty easy to do some detailed research if you have a particular need.

Recommended Greases

Here are the grease recommendations of some popular manufacturers. Note that Mobil SHC 100 is not available in tubes from Aircraft Spruce, but Amazon carries it. The smallest quantity available is a 4.4-pound tub for $83.

As you can see, AeroShell 22 is a popular choice among manufacturers. That said, AeroShell 5 also has a good track record. AeroShell products are widely available from aviation vendors, making them a popular choice among mechanics and aircraft owners. Matco recommends BG Products HCF 605 for wet uses and amphibious aircraft. It is available from SkyGeek. Mobil 28 is also popular as an alternative to AeroShell products, and Mobil SHC 100 is widely used by manufacturers during initial assembly. Since it is not available in tubes, it is much less popular with aircraft owners.

Mobil grease products are widely available from aviation vendors. Unfortunately, SHC 100 is only available in tubs, making it less popular with users who do not need large quantities.

Some Takeaways

Use a grease that is approved by the maker of the part you are greasing. The people who make your parts know best what works well for their products. In just about every case, that will mean using an aviation grease. Follow the lubricating procedures recommended in the manufacturer’s service literature. There are right and wrong ways to do most things. Do not mix greases—and especially do not mix mineral and synthetic greases. If you want to use a different grease, thoroughly clean the part before applying a new type of grease. Mixing greases can lead to corrosion and other negative consequences.

Popular Aviation Greases

BrandTypePrice/tubeUse
AeroShell 5Mineral$12.80Wheel bearings and engine accessories
AeroShell 6Mineral$10.75General purpose
AeroShell 7Synthetic$19.50General purpose
AeroShell 14Mineral$9.95General helicopter grease
AeroShell 22Synthetic$12.50General purpose, amphibious (Wipaire)
AeroShell 33Synthetic$17.50General purpose
AeroShell 64Synthetic$21.50General purpose
HCF 605Synthetic$10.76Amphibious (Matco)
Mobil 28Synthetic$14.75General purpose
Mobil 33Synthetic$17.95General purpose¹
Mobil SHC 100Synthetic$83.00/tub²General purpose
NYCO GN 3058Synthetic$27.00Hartzell props
¹Mobil 33 grease not recommended for wheel bearings
²Mobil SCH-100 not available in tubes, only 4.4-pound tubs or larger

 

[This article has been updated with the correct NYCO grease type and Mobil small quantity availability.]

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Dave Prizio has been plying the skies of the L.A. basin and beyond since 1973. Born into a family of builders, it was only natural that he would make his living as a contractor and spend his leisure time building airplanes. He has so far completed four—two GlaStars, a Glasair Sportsman, and a Texas Sport Cub—and is helping a friend build an RV-8. When he isn’t building something, he shares his love of aviation with others by flying Young Eagles or volunteering as an EAA Technical Counselor. He is also an A&P mechanic, Designated Airworthiness Representative (DAR), and was a member of the EAA Homebuilt Aircraft Council for six years.

4 COMMENTS

  1. Note on Mobil SHC 100 not being available in tubes, you can buy it in tubes on Amazon for $13.99. Been using on my RV-12 wheel bearing for several years.

  2. Great article on ingredients of grease Dave. Buy stock in Amazon but, buy your tube of Mobil SHC 100– at graingers.com under $8. Sorry for being late to the party.

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