The International Cessna^® 170 Association

N9149A wrote:So you guys running 4 ply tires. Do you think the side walls have more give than the same size and brand tire with the same pressure but with 6 plys?

Yes.

Yeah, although it's been so long since I landed something with 6 plys I couldn't say how big the difference really is.

This is so funny. How many times we all gather around here at the forums and argue about which dooma-flitchy-flop is stronger/better/longer-lasting and then we turn around and wonder which tire has the softest/flimsy-est sidewalls that might make our landings better.
A bad landing is a bad landing. A bad landing with a flimsy side-wall tire is harder on the flimsy side-wall tire than it would be on the sturdy side-wall tire. (Not criticizing the minimum-standard 4-ply tires certified for our airplanes. Just discussing the way we think.)
What are we looking for? Softer landings? Then spend more time practicing. Stronger tires? Then buy a stronger tire. (Can't help but imagine the owner who installs the stiff 180/185 gear because he thinks the early gear too springy,...then buys "softer" sidewall tires trying to make up for stiff touch-downs.)
Just laughing, guys. We're all so funny.

Thanks to all the good advice I installed my new Michelin 700 6x6 tires today. I learned quite a bit in the process. Having previously owned an aircraft with drum brakes, I was a little taken back by the disc brakes when it came time to remove the old tires. I got that figured out and installed the new tires following the advice from gahorn. However, when putting the tires/wheels back on the airplane, I discovered the pucks were dragging on the disk. I tried loosening the wheel nut, and tried loosening the bolts holding the removable pucks. Loosening the bolts to the removable puck just doesn't seem right to me. I am thinking about installing some sort of spacer, maybe a piece of sheet metal, to allow more space beween the removable pucks and the disk. I am sure others have dealt with this in the past and would welcome any advice. Thanks again.

Hold on there Robert. You need to tighten the wheel bearing nut just so. Not to snug, not to loose. There can be no play between the wheel, bearing and axle but it can't bind either.

As for the brake cylinder bolts, those need to be tight as well and there should be no shim installed between the brake shoe and the cylinder.

Disk brakes will drag a little. If you feel yours are dragging to much perhaps your wheel cylinders have gum and grim built up around the cylinder puck which will not allow the puck to recede into the cylinder when no pressure is present.

Try this. Take a large C clamp and use it to push the cylinder puck back into the cylinder a little so that when the brake is assembled there is no drag. Step on the brake. This should expand the puck applying break pressure. if when the brake is not applied there is more than a little drag left you need to look further.

These breaks are very simple but more than I want to get into here. If you need to get into them I suggest you get someone local to show you once. You'll be able to take care of them from there.

Robert,

Assuming you have Cleveland wheels and brakes, it sounds like you may have a similar problem to what I had after my airplane had sat for a while (many years ago). The brake assembly is supposed to "float" on the bolts that attach to the bracket, making them self-center on the first brake application after assembly. The attach bolts are actually pins with shoulders to prevent the cylinder from tightening against the bracket. If the brakes were reassembled at some point without antiseize on the pins, over time the pins can bind in their bores in the cylinder. Mine had to be pressed out... not good. If you can't wiggle the brake assembly a bit, then they are bound up. The brakes will still work somewhat due to the flexing of the bracket, but that shouldn't happen. There was a recent discussion on this forum as to what kind of antiseize compound to use on the pins.

Miles

The axle nut should be tightened against the wheel as tightly as possible BY HAND (fingers only, no wrench or pliers) ... then tightened additionally ONLY to the next-available hole which allows the cotter to be installed. This places the minimum amount of "pre-load" upon the wheel bearings without excessive tightening.
Sounds like the brake calipers are not assembled/installed correctly... or perhaps someone operated a brake pedal while the wheel/disc was removed (thereby expanding the pucks so they are not binding upon reassembly), or...nore likely...the pucks/calipers are simply a bit out of alignment. (While the wheel is still in jacked up, operate the brake pedals frimly, release them, then try to rotate the wheel again. The brake application will align the pucks/calipers/discs to relieve any binding.

Gentlemen,

FWIW...here I go again on my second favorite subject:

According to the charts DESSER used to have on their website, the 4 ply tires are about 2-3 pounds lighter (each) in any size than 6 ply tires. Noting the TCDS calls for 4 ply, there is no safety or performance reason to go with more than 4 plies as George explained, particularly in view of the newer materials. So much for the good news, BAD news is the 4 ply tires are rarer and more expensive than the more common 6 ply tires. Personally, I favor the more flexible sidewalls and lighter weight.

Curiously, AFTER flying my 170B prior to purchase, I checked the air pressure on the 800X6 6ply tires and found the pressure too low to be detectable on a standard automotive tire gage. Yet my Mark II eyeballs could not detect any significant tire deformation with the a/c resting in a three point stance during the pre-flight walk around and the plane handled fine on the ground.
My usual two centavos worth:
chuck

gahorn wrote:The axle nut should be tightened against the wheel as tightly as possible BY HAND (fingers only, no wrench or pliers) ... then tightened additionally ONLY to the next-available hole which allows the cotter to be installed. This places the minimum amount of "pre-load" upon the wheel bearings without excessive tightening. ...

I was taught that if you've just repacked the wheel bearings, to lightly snug the axle nut with a wrench to squeeze out excess grease, then finger tight as recommended above. Any thoughts on that George?

Miles

Well, I have to admit I am drawing on my training as a rear-axle specialist in the automotive world. (Got college and pilot's licesnse paid for, at least) Squeezing out excess grease is probably someone's quick-choice of description, but not really an issue. Excess grease should be removed with your fingers before the bearing is assembled in the wheel. This can be done very easily by hand when the roller/cone is place into the race. (Wheel bearings only require that sufficient grease be present to fill the space between the rollers. It's a good idea to buy a bearing greaser-tool, but the palm of your hand will also work. Don't just smear the grease on the rollers. Press the rollers against the blob of grease in your palm from the ends of the rollers, until the roller-bearing is filled with grease. Use your fingers to remove the excess,...and there's no need to squeeze out anymore. The small amount smeared all over the rollers by natural consequence is entirely adequate.) Using the hand, the installer can roll the cone about inside the race, which will spread the grease and test for smoothness.
(Roller bearings can take quite a bit of "pre-load" and still perform very well in oil. In fact, in oil, they require it. Rear axle differentials actually used a fairly high preload, but they are bathed in EP oil and kept pretty cool because of the oil bath. Such bearings also run in an environment which can transmit high noise levels to the "cockpit" via brake-lines to the master cylinder bolted to the sound-board known as a "firewall" in a car. The "cockpit" of a car makes a good sound box, and customers won't tolerate rear axle noise. Another consideration is the fact that rear axles have pinion and ring gears that must also be pre-loaded against each other or they will "sing" or "whine" due to the pinion's depth against the ring gear. For those reasons, high pre-loads (acceptable in oil baths) are required.)
Wheel bearings technically called "wheel end bearings" ,generally don't recieve much cooling except by convection and airflow. (Admittedly however, aircraft wheel bearings don't travel very far as a rule, compared to other vehicles.) The biggest problem with axle mounted cone bearings installation is "chatter". This is caused by excessive end-play which is removed when tightening the axle nut. But magnesium and/or aluminum wheels (which aircraft wheel bearings are mounted in) expands faster than steel. This means the wheel bearing will become less pre-loaded in service as the mechanism heats up. (The bearings are captive within the expanding wheel, not "floating" like in rear axle differentials.) The greater danger for wheel bearings come from water, dirt, and temperature.
The method you mention Miles, is practiced by auto mechanics and serves them well because the hubs of autos are steel running on steel races, and the much larger side-loads placed on bearing by autos/trucks require it. But in the automotive world, mfrs specify wheel end bearing preloads and/or torques (whether the automechanics actually avail themselves of that data is another matter.) But aircraft rarely do. Excessive bearing preload will result in higher heat, excessive wear, and premature replacement of bearings. My experience is that the casual home-mechanic places too much preload on axle bearings. What we are looking for is zero "end-play" or looseness, without excessive pre-load or crushing of the bearing. I don't use a wrench to tighten the axle nut on an airplane except when advancing it to the next cotter-pin hole, but it's important to have clean, undamaged threads so that handtightening will achieve zero end-play. Dirty threads can prevent the nut from removing all the end-play.
After hand-tightening, the act of further tightening to fit the cotter should guarantee the zero end play, while minimizing the chance of overloading the preload. (The use of tools to tighten the nut can place the nut slightly beyond a cotter-hole, then tightening to the next hole can push the pre-load to the limit.)
Whatever method you use, make certain the wheel cannot be moved axially (in/out) on the axle. Any movement at all is a sign that either bearing races are not seated in the wheel, or that the bearing is not being held sufficient to remove end-play. There should be zero end-play without excessive pre-loading the bearing. (The wheel, without brakes installed, should freely spin on the axle several revolutions before stopping.)

gahorn wrote: The method you mention Miles, is practiced by auto mechanics and serves them well because the hubs of autos are steel running on steel races, and the much larger side-loads placed on bearing by autos/trucks require it.

George,

George, if you'll notice in my post I did not recommend tightening the axle nut with a wrench and leaving it that way, just to do it initally to make sure everything is seated, then back it off and retighten as you originally suggested. I guess what you took a couple thousand words to say is that it won't hurt anything if you snug the axle nut, back it off, run it down with your fingers, then tighten just enough to insert the cotter pin.

Miles

"The biggest problem with axle mounted cone bearings installation is "chatter". This is caused by excessive end-play which is removed when tightening the axle nut."

Hey George I enjoyed the lengthy post and learned some things from it. Very interesting on the oil bathed info. In the quote above do you mean that if one of our wheel nuts is a little loose you can get a wheel or brake chatter? I've been trying to chase this down on my plane and perhaps this is the cause although I would think the nut would have to be awfully loose.

Dave all I know is if you let two nuts loose here at the forum you get a lot of chatter.

We got a smokin deal on some 7.00-6-8ply rated tires. Only problem is knowing when the tires are low on air. They look about the same with or without air.

cessna170bdriver wrote:

gahorn wrote: The method you mention Miles, is practiced by auto mechanics and serves them well because the hubs of autos are steel running on steel races, and the much larger side-loads placed on bearing by autos/trucks require it.

George,

George, if you'll notice in my post I did not recommend tightening the axle nut with a wrench and leaving it that way, just to do it initally to make sure everything is seated, then back it off and retighten as you originally suggested. I guess what you took a couple thousand words to say is that it won't hurt anything if you snug the axle nut, back it off, run it down with your fingers, then tighten just enough to insert the cotter pin.

Miles

Miles, I understood your original msg as you intended it. I just wrote the "long" version for those not familiar with doing this sort of work at all. Your last method mentioned (copied here) is good also.