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How much Main Wheel Drag?

Dbro172

Dbro172

Well Known Member
The plans indicate to snug down the nuts on the main wheels until a bit of drag is noticed, then back off one flat of the nut and install the cotter pin....

Does this mean that there should be absolutely no drag on the main wheels? As if they should spin freely? If so, what concerns me is the (probably immeasurable) amount of side to side "slop" on the wheel and bearings. Is this normal?

Should there be a bit of drag on the wheels? If there is a bit of drag intitially, does it decrease after a few T/O & Landings?
 
Wheels

Conventional wisdom....
1. When installing a wheel, always assume it is a weapon.
2. Always deflate said tire during assembly and dis-assy.
3. Red dot on tire goes where the valve stem exits the rim.
4. Use baby powder to dust the tube prior to placing tube in tire.
5. Always have someone else around to be able to call for help or render assistance.
6. Never just swap bearings without swapping the race as well.
7. If anything catches your nails on the race, swap the race and the bearings.
8. Muffler tubing from auto store works great for pressing the race out/in with the assistance of an oven and a freezer.
9. You pack the bearings and when you place them in the wheel assy, put some grease on top by hand prior to placing seals on it.
10. The bearing is torqued down to seat the bearing in the race, then it is backed off and re tightened to place everything back together. If you just torque it down, maybe it could mis-align slightly.
11. During tightening back down, you want the wheel to spin about 1.5 times and come to a complete stop. Then cotter key it.
12. Always treat it like a weapon. If you don't belive me, look up over inflating wheels on YouTube and watch them blow the safety cage apart.
13. Feel free to use new hardware when you reassy the wheels. Cheap insurance for sure. If you see discoloration, time to swap out your bearings.
14. Always follow the appropriate instructions and don't be afraid to ask questions.
15. If you have toe-in/out problems, put wax paper on the floor and roll over it to see what your wheels are doing.
16. If using multi-leg jacks, place a piece of paper under each leg during jacking to see if the jack is tilting to avoid your aircraft falling off the jacks.
17. Close the hangar doors as much as possible when you are jacking an aircraft.
18. If you are having shimmy problems, try lowering the tire pressure.
19. Never conect a high pressure bottle to your tire. Always have a low pressure regulator on a bottle.
20.Wear appropriate protection for what might happen.
Treat it like a loaded weapon. People have died doing this.
 
No, NO, NO

bruceh said:
I ran across this technical bulletin about preload on Matco's site.

The bearings with the integrated rubber dust seal need to be torqued between 18-26 inch pounds.
Click to expand...

John Thocker has taught me to read carefully - - This is NOT what the document says!!

"Manufacturers specification state, for example, that the two 1.25 inch tapered roller bearing used on the WE51 will produce between 18-26 inch pounds of torque (drag) when properly installed."

Note the BEARINGS will be properly torqued when the ROLLING TORQUE (the torque to turn the wheel) is 18-26 in-lbs . . . . NOT the nut torque!

Dbro172 said:
The plans indicate to snug down the nuts on the main wheels until a bit of drag is noticed, then back off one flat of the nut and install the cotter pin....

Does this mean that there should be absolutely no drag on the main wheels? As if they should spin freely? If so, what concerns me is the (probably immeasurable) amount of side to side "slop" on the wheel and bearings. Is this normal?

Should there be a bit of drag on the wheels? If there is a bit of drag intitially, does it decrease after a few T/O & Landings?
Click to expand...

Yes, there will be some drag. It is necessary to keep the inner races from rotating. And, yes, there is some break-in of the bearings after some use, then they stabilize. I don't know what the real world experience for our RV's is to recommend an hour check. Maybe some RV experience will speak to this as it was your original question.
 
Last edited:
Main wheel drag

One additional issue which I had only on the RV was the piston in the caliper easing out the inner pad against the disc and creating an artificial feeling that the bearing had seated when I was tightening the axle nut.
Happened twice while I was trying to figure out what the noise was during taxi until I removed the wheel pants and was able to see the wheels wobbling slightly when I pushed the airplane around.
Although this was over ten years ago, I'm still not sure how that managed to happen as I should not have had the brake pads against the disc When torquing the axle nut.
 
You can avoid brake drag by shaking the wheel with the bearing loose. Grab the wheel near the caliper and rock it back and forth before you snug up the bearing...... It will push the brake puck (piston) back just enough to free the pads from the disc.
 
I just put the Matcoe brakes on my -10 replacing the Groves. They use a bearing with an integrated rubber seal and require a different technique. You tighten the nut , rocking the wheel until the bearing is completely seated. Then you tighten until the seal does not rotate when you rotate the wheel. Then you tighten the nut more until a cotterpin will go in. There is quite a bit of drag at that point, but they are suppose to loosen a bit as the seal wears in.

They do have a bunch more stopping power than the originals!
 
Everything you always wanted to know about setting tapered roller bearings:
http://www.timken.com/en-us/Knowledge/ForMaintenanceProfessionals/Documents/5556-Setting-Techniques-for-Timken-Tapered-Roller-Bearings.pdf


Excerpt from the above ref.:
For example, in the case of a conventional truck non-driven wheel with a single adjusting nut design, manual setting involves tightening the adjusting nut while rotating the wheel until a slight bind is felt. Then the adjusting nut is backed off 1/6 to 1/4 turn to the nearest locking hole or sufficiently to allow the wheel to rotate freely with some minimal end play. The adjusting nut is then locked in this position.
 
Great find Walt. That one goes in the reference file.

Here's the money shot.



It suggests zero freeplay or maybe just 0.001" of preload is "perfect", but that there is no realistic downside to the classic field method for wheel bearing set (as quoted by Walt) because we get up to 5000 hours with axial freeplay as large as 0.008".

The standard thread is (I think) either 1-1/4"-16 or 1-1/2-16. With 16 threads per inch, each rev is 0.0625" axial movement of the nut. Divide 0.0625/8 = 0.0078", so backing out 1/8 turn from zero-freeplay tightness is the limit. Most of us are backing out from drag tight, a point with axial preload, and probably wind up 0.004" or less.
 
Bottom line is where the hole was drilled is what you have to work with. So, you are better off with a little free play than too much preload, so tighten to eliminate end play and unless you are very close to the hole at that point then you will need to back off to the next slot.
 
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