8KCAB Tires and Wheels

EJWash

EJWash

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Hi All, Taxied my 1975 8KCAB from an open hanger (planeport?) to an enclosed hangar on my airfield. Low ceiling, so no flying. When I went to push the plane back into the hangar, I met great resistance. Well, the left main gear tire was flat! It had to have just happened, as taxi was smooth and uneventful. Welcome to airplane ownership! After ordering a jack pad from Bogert, I removed the tire and brought it home. Great. Now I need to order a bead breaker. Once I solved the tire issue, hopefully just a tube gone bad, any advice on cleaning the wheel? It looks like the 1975 original to me, and I didn't see anything about R&R in the logbooks. It went through Annual in September of '21. Axle and bearings look greased. Or, is greasing a normal practice when a wheel is removed? What type of grease? Thanks!
 
EJ,

I've been helping my IA friend in his shop while he has been trying to hire a new person. His routine is to always wash the bearings and seals in avgas (outside), blow them out with compressed air, and then regrease the bearings with the red synthetic stuff and oil the felt seal with 3-in-1 oil which is basically the same as the straight weight oil that is specified.

maybe others will agree, we'll see.
 
Yeah. Can’t be too careful with wheel bearings. Just remember that a bearing failure on a Decathlon is a non-event. Just makes noise. Yet the outer front bearing on your 1965 Mustang is the same size and manufacturer - and gets as much wear and tear in a day as your Decathlon bearing does in a year. A failure of an outer bearing on a Mustang probably means the loss of a wheel, and possibly a life! Lightplane bearings cannot get that hot unless you taxi on the freeway at 65 mph.

Hopefully you all do your auto bearings at least every six months?
 
bob,
i'm not an A&P or IA but from what I've seen, the grease from an airplane wheel bearing doesn't have much keeping it in the bearing so any chance you have to clean it out and repack it, it's worth the effort. granted, the wear on a typical light airplane bearing is minimal, but why not service it when you have the chance?
 
My point was - it is far more critical on an automobile, yet nobody ever does it routinely. I watched a guy repack a brand new set of Grove wheels - they had about five hours on them. I said "why are you doing that?" He said "it's required."

Auto grease is different - it runs at higher temperatures. Our wheels typically need lubrication when cool.

I realize I am odd man out - but I have had two auto wheels leave the vehicle, one at 70 mph (repacked and overtightened by a Ford dealer) and the other in a parking lot. I have never had a lightplane bearing fail. Early Cub bearings were greased wood blocks,
 
Thanks fellas. Any thoughts on cleaning up magnesium wheels?

On another note, I'm thinking that I should give the same exact treatment to the right tire/wheel. If the left went south, how much more time before the right follows? I mean, both tires/wheels are in the same environment.
 
EJWash said:
Thanks fellas. Any thoughts on cleaning up magnesium wheels?

On another note, I'm thinking that I should give the same exact treatment to the right tire/wheel. If the left went south, how much more time before the right follows? I mean, both tires/wheels are in the same environment.
Click to expand...
It depends on the failure mode. A nail in the tire? A pinched tube? If so fix the flat, grease the bearings and go flying.
If you find a valve stem sheared (due to low air pressure) then by all means check the other side for proper inflation. Ditto if the bearings on the wheel you're working on are dry or the grease is filthy/gritty...do the other side too.
BTW; have you ever changed an aircraft tire out before? If not you may want to find an A&P or EAA member to show you the do's and don't 's...it ain't like changing a bike inner tube. And getting something wrong could cause problems down the road (runway).
Chris
 
Hiperbiper said:
It depends on the failure mode. A nail in the tire? A pinched tube? If so fix the flat, grease the bearings and go flying.
If you find a valve stem sheared (due to low air pressure) then by all means check the other side for proper inflation. Ditto if the bearings on the wheel you're working on are dry or the grease is filthy/gritty...do the other side too.
BTW; have you ever changed an aircraft tire out before? If not you may want to find an A&P or EAA member to show you the do's and don't 's...it ain't like changing a bike inner tube. And getting something wrong could cause problems down the road (runway).
Chris
Click to expand...
Hey Chris,

Thanks. I haven't gotten as far in the tear-down process where I can ascertain the issue. No, I haven't changed an airplane tire before. Although, getting A&P help in my parts is months away. Without hand's-on guidance, it's You Tube leading the way.
 
The problem is pinching the tube between the wheel halves. Sometimes you can collapse things and get a visual or a "feel", but sometimes you have to rely on the "click, click" of wheel halves hitting metal to metal.
Pinched tubes are more common than you might think, and often will hold air until some really heavy braking event. They can also cause brake disc wobble.
 
Bob, I can't think that tubes all of a sudden get pinched between the wheel halves. Or, is this possible?
 
That was the part you were addressing - how to change a tire. No, of course they don,t break those bolts and sneak up inside the wheel half during operation.

Almost everything else about Cleveland tire changing is straightforward. Don’t forget to put the disc back on.
 
You don't need special tire tools like a bead breaker. Unlike a car wheel, the halves of the aircraft wheel pull apart when the thru bolts are removed.

The main difference between aircraft bearings and auto/trailer bearings is the lack of a watertight seal on the axle. Boat and car bearings have a double lipped rubber seal on the inner axle, while our planes just have a felt ring. 99% of the time when a boat or car axle fails, it is because the seal failed and let water in.

I used to tow my boat a lot. 500 mile trips on the interstate at 70 mph. Combined with dunking in the ocean weekly, that is a very demanding environment for bearings. The slightest salt water intrusion into the bearing will cause corrosion and failure, which melts down the bearing and destroys the axle in spectacular fashion, usually on a Sunday night in a rural area. So if you are serious about trailering and you operate in the ocean, you repack your bearings every year or you eventually learn your lesson the hard way

But an airplane is not a boat trailer. For a hangared aircraft flown in fair weather, you could probably go 10 years between repacks without problem. Having said that, those bearings do not have a watertight seal, just a piece of felt to keep moisture out, so they do need to be greased on a regular basis. As Bob points out, bearing failure in a taildragger is a non-event, just some extra noise.

Boat trailer bearing hubs are an unholy mess. I've tried just about every possible degreasing substance possible. IMO the best is mineral spirits. Toss in a dish, let soak for a bit, then clean out the nooks with a parts cleaning brush, blow out, hit with a shot of brake cleaner to dry, and repack. Do not allow the bearing to spin if you blow out with compressed air.
 
Yes! And guess how often we re-grease the Wipline bearings? Every single flinging time the aircraft lands on water. Even though the wheels really don't rotate much.

Most autos go five years between repacking. Sure, those rubber seals are better - but they wear out almost as fast as prop seals. I am currently getting ten years on C-85 prop seals - and admit that my 65 Mustangs have never had new bearings or seals.
 
Yep. Falcon bearings - teeny things; probably the inners are Decathlon-sized. It is the small outers that die - they are almost as small as Scott tailwheel bearings.
 
My newer Corvettes have complete hubs that are replaced.
When they chatter in a turn they get replaced.
The old ones have simple tapered roller bearings just like our aircraft have.

Chris
 
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