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Airplane Maintenance for the DIYer: Changing a Tire

Airplane Maintenance for the DIYer: Changing a Tire

Published in Maintenance & Technical.

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In this article—the first in a series describing various preventive maintenance actions—A&P Jacqueline Shipe goes through the entire process of removing and reinstalling an aircraft tire. 

All aircraft owners will periodically have to replace a tire. Even planes that don’t get used much eventually require tire replacement due to dry rot and sidewall cracking of the rubber. 

Tire replacement is one of the items the FAA considers preventive maintenance that owners may legally perform on their aircraft. Changing a tire isn’t mechanically complex, but it does require the owner to use some caution. 

Proper aircraft jacking procedures have to be used, and if the plane is jacked outside, first check the weather conditions to ensure that the wind is not going to be too high. Major damage can be done to the airframe structure whenever a plane falls off a jack. 

Once the plane is properly jacked, the removal of the wheel assembly can begin. (For information about aircraft jacks and proper procedures, take a look at Shipe’s “Airplane Maintenance for the DIYer: First Steps” in the May 2016 issue. —Ed.)

If the plane is equipped with wheel pants, the wheel pant has to be removed first. This is usually a pretty straightforward process, just be sure to keep the removed screws and bolts identified as to which receptacle they came out of, because sometimes several different diameters and lengths are installed. 

Removing a main wheel

The next step is to remove the outboard brake backing plate (if the wheel is a main wheel) so that the brake disc will be free to slide off the axle with the wheel assembly. 

There are two or more bolts that connect the backing plates to the caliper that have to be removed. They may or may not have safety wire on them, depending on the design. 

Once the outboard brake is off, the next step is to deflate the tire by removing the valve core. It is important to do this before removing the big axle nut, because if any bolts holding the wheel halves together are loose or damaged, the wheel assembly could blow apart as the axle nut is loosened. 

Most axle nuts have either a clevis pin with a small cotter key or a single large cotter key to keep them from backing off. 

When the axle nut is removed, the wheel assembly will slide off. Some manufacturers employ a spacer that may or may not slide off with the wheel; care needs to be taken to ensure it doesn’t get misplaced.

Removing a nosewheel

Nosewheels usually have a removable axle that slides through the wheel and nose fork. This is generally held in place with a single long bolt and lock nut that secures two cup-shaped retainers. 

Nosewheels are fairly easy to remove unless the steel axle is corroded and frozen in the aluminum fork, in which case the axle has to be driven out. A wooden dowel should be used to drive out the axle because it won’t gouge or mar the aluminum fork.

 

Breaking the tire bead

Once the wheel is removed, the tire bead needs to be broken from the rim of the wheel halves. Get a piece of plywood to lay the wheel on (so it won’t get marred), then forcefully push the tire down all the way around. It will eventually pop down off the rim. This process has to be repeated on the reverse side as well. 

Some folks use flat blade screwdrivers or pry bars to pry the tire away from the wheel, but this can result in major scarring of the relatively soft cast aluminum that the wheels are made of. 

If the bead is really stubborn and just won’t break loose, you may have to enlist the help of a mechanic and a bead-breaking tool made specifically for the task.

Splitting the wheel and removing the tube 

Most wheel assemblies are two-piece, and the wheel halves are split by removing the through bolts and nuts holding them together. After separating the wheel halves, the tube can then be removed from the tire. 

Some mechanics replace the tube with every tire change, and some re-use the old tube as long as it looks good. Tube manufacturers recommend always replacing tubes when replacing a tire because they stretch while in use. 

Once an old tube is removed, it can be barely inflated—just enough to expand it a little—so the entire exterior can be inspected. Tubes with deep wrinkles or that have signs of damage or age, such as dry rot cracks around the valve stem, should always be replaced. 

When ordering a replacement tube, pilots may want to get the type that doesn’t lose air, such as a Leakguard or Airstop inner tube. They do reduce the frequency of having to air up the tires by quite a bit, especially if they are serviced with nitrogen instead of compressed air. 

Reinstalling the tube

The outside of the tube and inner part of the tire need to be coated in talcum powder before installing the tube. The powder keeps the tube from sticking to the sides of the tire and helps prevent chafing. 

The tube should have a balance mark on it. This needs to be aligned with the balance mark on the tire, which is generally a red dot. 

In the absence of a balance mark on the tube, align the valve stem with the red dot. This matches the heaviest part of the tube with the lightest part of the tire and makes it much easier to balance.

 

Reassembling the wheel

Once the tube is installed in the tire, the wheel halves (and the brake disc, if it is a main wheel) can be assembled together. Slightly inflating the tube a tiny amount helps to ensure it won’t be pinched between the wheel halves. 

Place the wheel halves together so the bolt holes align. The bolts can then be slid through and the washers and lock nuts installed. Lock nuts should have enough tension on them so that they cannot be tightened by hand, otherwise they should be replaced. 

The correct torque should be observed when assembling the wheel halves. These are made of cast aluminum and are strong, but over-tightening the nuts and bolts can lead to cracking. 

 

Balancing the tire

A wheel balancer is a fairly expensive tool to buy, and tires aren’t usually replaced on an individual airplane often enough to merit owning one for most folks. Large imbalances in a wheel assembly can be detected by mounting the wheel on the axle and installing the axle nut, but leaving it slightly loose so the wheel rotates freely. 

Once the tire is spun a few times, if the same spot always ends up coming to rest on the bottom, this indicates an imbalance and weights will need to be added to the light side. Using stick-on lead type weights purchased from an aviation parts warehouse or automotive store, add enough weight so that the wheel comes to a stop in random places as it is spun freely on the axle. The balance is more critical on the nosewheel assembly because it will cause a shimmy if there is even a slight imbalance. 

 

Reinstalling the wheel on the aircraft

Once the wheel is balanced, it is ready for installation. The axle should be wiped off and greased, and any corrosion should be removed with an abrasive cleaning pad. 

A general-purpose Scotch-Brite 7447 pad (maroon color) works well and can be purchased anywhere automotive paint products are sold. These pads are abrasive enough to clean off rust, but not so abrasive so as to scratch the metal. Use elbow grease to scrub the axle until it is shiny.  

The nosewheel axle is prone to rusting internally. Any rust should be removed here too, and the internal part of the axle should be either painted with a rusty-metal primer, or coated in LPS 3 or other corrosion-inhibiting compound. 

During the final installation, the axle nut needs to be tightened enough so there is no free play detected as the tire is grasped and pushed inboard on the top while pulling outboard on the bottom, or vice versa. (This checks for side-to-side free play, and there should be none.) 

The wheel should spin somewhat freely, but there needs to be a slight amount of tension on the axle nut. If the nut is too tight, the wheel won’t spin much at all by hand, and the wheel bearings will be more likely to fail from having too much of a pre-load placed on them. 

Once the correct tension is achieved, align the cotter key hole in the axle with the opening in the nut and install the cotter key. Be sure to bend the edges of the cotter key in such a way that they won’t get entangled in the valve stem or rub on the wheel bearing retainer. 

After the wheel is secured in place, the valve stem should be removed and the tube inflated and deflated two or three times to remove any wrinkles. Then the valve stem can be reinstalled and the tire inflated to its proper pressure. (Correct tire pressures are found in the POH.) 

After the outboard brake and/or wheel pant are reinstalled, the tire change will be complete. The aircraft owner will also have the satisfaction of having completed the work himself (or herself)—and will have hopefully have saved a few bucks in the process.

 

Jacqueline Shipe grew up in an aviation home; her dad was a flight instructor. She soloed at age 16 and went on to get her CFII and ATP certificate. Shipe attended Kentucky Tech to obtain her A&P license. She has worked as an airline mechanic and on a variety of General Aviation planes, and has logged over 5,000 hours of flight instruction time. Send question or comments to .

RESOURCES >>>>>

Leakguard butyl inner tubes by Aero Classic
Aircraft Spruce & Specialty
aircraftspruce.com
Airstop® aircraft inner tubes
Michelin North America Inc.
airmichelin.com
LPS 3 Premier Rust Inhibitor
ITW Pro Brands
lpslabs.com