Nosewheel bearings

Guys (those of you with a nosedragger),

I still don't have my wheel fairings on. This weekend during preflight I noticed some black goo, tar-like stuff oozing out around the rubber bearing seals on my nosewheel. It did not appear until I had about a dozen landings on the airplane. Since the grease that was in it originally was the normal amber color I was a bit surprised to see this color, and also a bit surprised to see it leaking out as it had been perfectly clean up until this point. Anybody else seen such a thing?

I also checked the rolling friction of the tire and it is still REALLY stiff to turn by hand. I know that when a wheel is properly installed there should be enough load on the bearing to provide friction....i.e. it should not continue to spin around freely after you give it a whirl by hand. But from the first time I installed the nosewheel--properly torqued per the plans with a calibrated wrench--it seemed excessively stiff to me. I remember the plans said that it would be this way until it was broken in a bit. I don't know how long that should take but I checked the nosewheel on my hangar mate's new -7A (with fewer hours than I have) and his wheel turned much easier. I tried loosening the nut on the axle bolt and that made it turn more freely but then I noticed that the spacers were spinning too. I torqued it back up and now it's ridiculously stiff again. My hangar mate's -7A has the wheel pant installed so I can't see whether the spacers are spinning on his. I called Vans and Gus said that it's quite common for people to call and complain that the spacers have been spinning instead of the bearing and galling up the fork assembly. He suggested that I could put some screws in through the fork into the spacer to keep them from spinning. This would allow me to reduce the pressure/friction on the bearings, but he cautioned against reducing the torque on the axle bolt too much since Matco calls out 7-10 ft lbs for this assembly.

Personally I think the whole design is a bit iffy from the perspective that there's a very small margin between having enough pressure to keep the spacers from turning without so much pressure the that rotational friction on the bearings/seals is excessive. It makes me wonder how many people are flying around out there with the wheel pants on, completely unaware that the spacers are spinning away while the bearings are doing nothing. On the other hand, if the rotational friction is excessive it *may* have contributed to some of the bent nose gear incidents that have occurred in recent years. It's pretty scary watching the nosegear at high speed, even during a good landing....the more rotational friction, the further the gear is going to bend back/under when it first makes contact at high speed. I think I'll disassemble the whole thing, check the bearings for overheating, repack them, put screws in through the fork/spacer assembly, and tighten it up until it feels "about right".

Any comments/experience from others with this assembly would be appreciated. FWIW, I understand that the -6A's had a different design (which some local RVators consider to be superior to the current design...).

Thanks,

--Mark Navratil
Cedar Rapids, Iowa
RV-8A N2D flying 15.8 hours

Hi Mark!

Looks like your getting some hours on the 8! Sorry, no advice from me on this. Just got in from the shop where I've been working on fluting wing ribs and saw your post. Thought I would say hi.

Hope someone has a good answer for you. Good luck!

I had the same problem on my 6A that was the first RV that I built. When i called Vans and told them that the spacers were spinning on the axle bolt they told me they never heard of such a thing. I never put much stock in what they told me after that. I think I was the first one to drill and counter sink for a # 10 screw to hold the spacers. For double measure i steaked the bearings to the spacers. I did the same thing on my 7A. After you do this you can take some pressure off the bearings and let the wheel rotate more freely

casper said:

For double measure i steaked the bearings to the spacers. I did the same thing on my 7A. After you do this you can take some pressure off the bearings and let the wheel rotate more freely

Click to expand...

What do you mean by "steaked the bearings to the spacers"? How did you do this?

--Mark Navratil
Cedar Rapids, Iowa
RV-8A N2D flying 15.8 hours

Rv-6a

I have no fluid coming from the hub after 176 hours but during the recently completed Annual Condition Inspection I observed the resistance to rotation of the nose gear and I backed off the axle bolt enough to get some rotation after my hand left the tire. It resists rotation and it does not wobble but the amount of resistance before was more like a nose skid than a nose tire. I have only made three landings since then but they all seem fine. Not very scientific I'm afraid.

I would have to find out where the black stuff is coming from if I were in your shoes.

Bob Axsom

czechsix said:

What do you mean by "steaked the bearings to the spacers"? How did you do this?

--Mark Navratil
Cedar Rapids, Iowa
RV-8A N2D flying 15.8 hours

Click to expand...

Mark: you asked how do you steak the bearings to the spacers. I used my center punch. On the spacer where the bearing race rides you center punch the spacer 5 or 6 places. You will have to drive the bearings on the spacer, but that is the idea. You don't want the race spinning on the spacer

I drilled and tapped the mushrooms for # 10 countersunk screws to hold them to the fork. The axle washers cover the screw heads and prevent them from backing out. This really helped reduce the load on the bearings and allowed the wheel to spin more freely. It still isn't as free and the mains. I think that the seals add a little drag yet, but much better.

I personnaly think the load on the bearings, using 15 inch lbs on the axle nut, is too high. Now I adjust just to remove any slop and daylight between the fork and the mushrooms.

JMHO

Roberta

Here is a shot of the CS screw held by the washer. The wheel pant bracket will do this when reinstalled.

This "new" design where the bearings take the compressive load of the axle bolt is stunning. The older (I don't know how old, but my finishing kit was circa 1997) setups had a hollow rod machined from aluminum all the way through from one fork to the other to take up the bolt load. The bearing preload was at the mercy of the tolerance stackup, but still a much better design than the current. A couple years ago, one of our 7A builders here was telling me that there was no carry-through, and I simply couldn't believe him, because what he was describing was an exceedingly poor design. Anyway, after this thread started, I believe it.

If I had one of these I would find a way to put a hollow shaft of some sort through there immediately. Use shims to get the bearing preload right.

Sheesh.

Alex P.

I Totally agree, Alex. My Cherokee had a better axle design. At least staking the mushrooms prevents them from spinning and spinning the axle bolt. It also allows you to regulate the preload better than using a bolt torque. Maybe this could be some area a good machinist could make a retro and use a hollow axle that carries through the fork.

Roberta

As an alternative - perhaps you can modify to

The Lancair uses a "mushroom" type spacer, but from the outside. It has a notch cut in it and there are matching brackets that attach to the side of the nose wheel fork to prevent it from spinning. Then uses an axle with a hole thru it and a long bolt.

Attached is a screen shot of the manual as a reference point. While this is the RG version, the FG is the same attach mechanism just with a wheel pant.



Perhaps this will give you some ideas?

Alan, do the parts labelled "axle bushings" come together in the middle? Or, as with the newer Van's design, does the bolt torque affect bearing preload?

Alex Peterson

No, they don't

The "axle bushings" don't touch in the middle. The bolt sets the pre-load. As a matter of fact in order for me to slip the wheel/bearings/bushings into the fork I have to spread it very slightly. I emphasize "slightly". It's easy enough to do with my fingers but the point is, there is NO clearance at all.

Too bad Van's did not use this setup. It looks like it could be adapted to our forks by machining the axle hole to fit the mushrooms and tapping in some holes for the keepers. A new mounting system for the pant would be needed. Do you have any shots of how the fixed wheel pant is mounted?

All wheel bearings are loaded by a bolt and/or nut. The problem is when the bearing is overloaded in an effort to prevent the assembly from turning on the axle bolt as is the case with Van's. At least staking the mushrooms resolves that issue. I do like the Lanceair axle better.

Roberta

Dumb question, and I think I know the answer, but does the tow bar go on the axle nut or the two screws that hold the wheel pant on? I bought the 9A second hand and the builder used the axle nut. During the condition inspection I noticed the galling mentioned here, so I'm trying to eliminate all problems. I think the "force of the tow bar has weakened the fork just enough to allow the mushrooms (spacers) to spin. The bearings were turning on the mushrooms also.

I installed 2, 10-24 screws to hold the spacers in place after "Swedish knurling" the surface the bearings ID rides on. IMHO the seals are causing the heavy drag. At least they don't spin in the air.

Matco wheel

This wheel is a very poor design. I have both the Matco and cleveland setup so I can change tires easily. The Cleveland wheel has a real axel that is slightly shorter than the units that put pressure on the bearing race. I have problems when I use the Matco because of the huge rolling resistance , but no problems with the Cleveland

To prevent rotation of the spacers, the machine screw process described (with photo) by Roberta is sufficient. As far as setting load on the bearings, the objective should be zero endplay and zero preload. The old school thought was that by adding "some" preload, end play is eliminated and bearing life is improved. Problem here is that it is very difficult to measure how much load is actually being introduced, especially when this is done using torque. Torque to clamp ratio is highly variable and is greatly influenced by friction (thread form and the presence or absence of lubricant on the thread and clamping surfaces. That's why torque angle is used on critical faster applications. Preload on a bearing can lead to premature failure. If the wheel rotation is tight after installation, you are causing damage to the bearings.
Terry
RV9A
N323TP