Front Axle and Fork Wear Issue
Added 8/9/2006 -
Updated 9/16/2006 - Updated 1/20/2009
NOTE: You can read this page, but don't read it as the "final
Once you finish this page, CLICK
HERE for the 1/20/2009 update, where an entirely
new fix for the issue is reported.
I've just run into an issue that I'd heard about once
and actually investigated at one point. It's turned out to be
something that I would consider fairly serious. Back when I
had installed my wheel fairings during or just after my 25 hour flyoff
period, I had heard about someone being concerned or having issues with
the sleeves around their axle rotating and wearing on their forks.
They determined that there is not enough pressure against
thin sleeve that pushes the bearings against the wheel to keep it from
rotating around the axle shaft, and when it rotates, it causes wear on
the forks, since they're aluminum. The person at the time
watch to make sure yours aren't turning on the shaft, and that they
called Van's and they sent him a set of shims, or some parts of some
type that fixed the issue. A couple other builders also
Well, not being one to ignore a problem if I know about it, and having
experienced a slight nosewheel shimmy on deceleration after installing
the wheel fairings, I called Van's for myself and told them that I had
heard about this issue, and that they had some parts that could be
requested or sent out. The person I talked to had no idea
was talking about and didn't seem to think there was an issue.
So, satisfied for the time being, I thought I'd watch it and see how it
Now, 107 hours later, I'm not a very happy camper. I had what
seemed to be a slight nosewheel shimmy on touchdown, only between about
45 and 35 kts. I had one shimmy yesterday that seemed worse
normal, so tonight I jacked up the plane and thought I'd look at the
axle and look for wear.
First of all, it is NOT apparent by just an assembled visual
inspection. With the fairings off, I didn't see anything out
the ordinary except for the fact that my bearing rubber seals had been
torn up a bit. Then I looked a little closer and found that
valve stem which was before just very close to the fork for the whole
25 hour flyoff, had been now bumping the fork slightly. So I
pulled the wheel off and that's when the fumes started coming off my
head. As soon as the wheel was off, it was easy to see that
collars on the axle had indeed been rotating. The wheel had
loosened a LOT and easily could flop side to side at least 1/8" due to
Part of it is caused by the collars wearing into a taper where they
meet the bearings. If the collars were about twice as thick,
would be MUCH better in this respect. The worst part though
that the grooves were worn pretty deep, effectively loosening those
collars a huge amount. The groove on the right side of the
in the photos is probably about .020" deep. But the one on
Left fork is .040" deep....which is HUGE. Immediately I
to wonder about the integrity of the fork itself, but for now I'll
assume that it is still OK, or that I can at least still deal with it
Look closely at the collars below. The outer sides are still
fairly flat, but they were the side that ground the grooves into the
forks. The inner sides are tapered as they hit the curved
the bearing near the center where it rides on the axle shaft.
Look closely at the rubber seal. It's torn, and
pieces missing. Even the axle itself shows a little wear from
where the rotating collars wore it a little.
Now for the fix:
Please refer to 1/20/2009's update HERE
Tomorrow I will be calling Van's, and I'll show them the photos if
they'll take the time to look. If they have a fix, I'll try
get it sent overnight so I can continue my flying plans that I had for
the weekend. Hopefully the forks are acceptable....my guess
they could be. If they were less than $100 though, I'd
buy them for peace of mind. At 107 hours, it's pretty
to find something that can cause this much permanent parts damage.
Barring anything else from Van's, there is one fix that I would
strongly suggest people think about. (of course, if there's
official fix that they'll publicize, use that one) I would
suggest putting a very large Stainless Steel flat washer just inside
those forks, and shorten the axle shaft by the same thickness as the
washers. I'd also shorten the collars, but not by the entire
thickness of the washers. This is because those collars will
wear into a taper again. IDEALLY, the collars would be
by something twice as thick. The large flat
to be large enough that they're bigger than the collar diameter, so
that if the collar ever spins again, it will rotate against the steel
washer, and not the aluminum fork.
Next, you need to keep the collar from turning. My thought
drill and tap a hole through the fork side, right where that groove
ended up, for a 10-32 allen head lock screw. Then, on the
shaft, and collar, you would notch the collar slightly, and place the
axle in place and drill into the axle itself a little hole.
way you can then insert a screw, or allen head lockscrew from the
outside of the fork, and have it end up right between the collar and
axle, preventing it from rotating. You could do the same
in a couple different ways, but this should work.
One other part of a fix should include improving the way the collar
meshes with the bearing. As previously mentioned, it would be
much better if the collar was twice the thickness. Barring
it may be a good idea to pile on some JB weld or something to the
intersection of the collar and bearing. This will possibly
and help prevent the bearing inner race from rotating on the axle shaft
as well. The fit is too loose to easily prevent the bearing
rolling on the shaft, so something should be done about that.
In an ideal world, you could have the axle shaft thicker in the center
where the bearings are, and thinner on the outer edges. This
allow you to use stacked washers as shims to adjust the bearing preload
separately from the axle bolt tightness. Or even for the
system, perhaps a couple of large but thin nuts could be used on each
side to tighten the bearings and then the 2nd nut to lock the first one
from backing out. At any rate, if there is someone with
to a machine shop, this could be a good opportunity to redesign this
axle area and make some bucks because now that I've really had the
chance to ponder it, the design was completely deficient in the first
place. It should have been designed better from the start, so
that none of the common wear parts would take out that expensive fork,
or cause an accident by cracking the fork ear off where the metal
to page 46-06 on your plans for visual information
I both figured out an idea, and just got off the phone
at Van's. Yes, they are aware of the issue.
did change the U-1023 spacers that are delivered with the kits and now
instead of thin stainless steel, they're thick aluminum spacers, that
should spin less easily, especially stuck against the similar aluminum,
as it might tend to gall and stick. He didn't know why they
didn't make it an S.B. and send out new parts. So, this is
DEFINITELY something to address for anyone who hasn't yet, and these
parts should be available free. This isn't to say that the
fix is ideal, but certainly better than what I had to fly with for 100+
The NOSE FORK ASSY part is somewhere around $160, for those who are
interested. I may end up doing that, depending on how
am....which remains to be seen.
I am getting the new spacers via UPS ground, instead of overnight,
because I also have one other thing that I'd like to try and
accomplish. Personally, I think I know what needs to be done
protect those forks. Today at fastenal I found 3/8" ID x 1.5"
stainless fender washers and they're .050" thick. A very
Aviation hardware washer would be the AN970-6, which are only 12 cents
at Van's and are 1-5/8" diameter and .063 thick. The idea is
that if that U-1009 axle is cut down in length by the same thickness as
2 of those washer, you could then install a large-area flat washer
against the fork, and that would prevent EVER having that fork wear.
You never want to unnecessarily wear an expensive part.
So, on my order is a few AN970-6's, -7's, and a new U-1009 axle.
The axle was about $15, and I ordered it so that I could
these parts to ship UPS ground, and still feel good about chopping up
my old U-1009 and shortening it at a local machine shop so I can put
these washers in for the weekend. If the new spacers work
with my shortened axle and washers, then I will just leave it that way
permanently. Small price to pay to fix the issue fast....less
than an hours' flight time. The bigger problem is until I
get over it, or buy a new fork assy, I'm going to have that nagging
thought of the fork damage. There's still about .290-.300
thickness to that fork, which should be good, especially if you hold
that nosewheel off well on landing.
More photos to come as things come together...
8/10/2006 Update (p.m.)
Today I stopped by a machine shop and had them take off
.115" off my axle, to accomodate 2 AN970-6 washers on the outer edge.
Yes, they are .063 each, so .126" would have been the
but I wanted the axle to be even just a little more snug than before,
because any flexing inward will bring that valve cap closer to the
fork. As a side note, this from John D. today...a
someone sent him:
"returned the nosewheel to Matco to have it replaced with WHLNW511.25
which is correct for the valve stem on the tube and avoids the
clearance problem with the supplies WHLNW501.25."
In other words, Van's is sending out the wrong wheel for the
application on this plane...because they use this wheel for the RV-7's
and such, and didn't want to have to stock 2 parts. So we get
receive the one that isn't made for the application, and therefore
unless you swap wheels, you're going to have minimal valve stem
clearance.....pretty nice, huh? <not>
Anyway, I had the axle cut shorter at a machine shop, and then I just
had to guesstimate how much to take off the 2 spacers.
they had worn into a taper on the inside, to fit against the bearing, I
had them only cut down by .085" total. I did .035" on one
and .050" on the other. That way I could have a slightly
sleeve on the left side, so my valve stem had just that little extra
clearance from the fork. This brought forth a small
problem... Tonight when I assembled it as in the first photo
below, it looked great. VERY much better than original.
Then, when I put the whole wheel together, I found that the
spacers had worn probably at least .120" because there was tons of slop
in the spacers yet, even though they now had a nice flat surface to sit
between, and had been cut less than the axle, and the washers were in
there to fill in some space. The spacers just spun.
decided since I already ordered another axle, I'd take my bandsaw and
VERY carefully trim off some more axle, and just use one more washer on
the left side. That should keep that valve stem even FURTHER
away. If I was right, I could get it so there would be plenty
pressure on the bearings and spacers to hold them in place so they
don't spin. Sure enough, it worked just great. I
torque that bolt down tight and keep the spacers from spinning, and the
bearing too. Just to be totally sure they never spun again, I
drilled a couple of holes in the stainless spacers, and remounted it
all. Then I made a pilot hole in the aluminum axle shaft, and
took it all apart and tapped it for an 8-32 screw on each spacer.
Then I cleaned it up, regreased, and put it all together.
Now it is very solid, and should never wear the fork
just am left with a crappy fork...so I'll probably just get a new one.
Once my new spacers and axle come in, I may tear it all
and use those pieces, but I'll still probably cut the axle and spacers
down and use the washers on the outer ends. It will prevent
forks from being the sacrificial component. The bearing, for
future reference, is a Timken LM-67000L-A. About $25 at the
local bearing supply shop or Van's.
A note about tightening the axle nut... Tonight on the RV-10
list, someone said that George Orndorff (A Van's tech center place),
says that the bolt should only be snugged, and then rechecked often in
the first few hours. I don't personally believe this is true
the RV-10, but perhaps it is on the other models. Here's why.
I studied this long and hard, and now I fully understand why
this is such a huge freaking issue. It didn't make sense at
first, having worked on dozens and dozens of automotive bearings in the
past. You see, on automotive apps, the bearings are pressed
the backside, and a nut and washer holds the bearing tight.
it pushes against a different area of the bearing. And the
seal is usually a seal that is pressed into the hub, with a seal around
the shaft on the ID of the seal. This is NOT how these
are on this application. On THIS application, you are
that the sleeves, the axle, the bolt, AND the inner race area of the
bearing do not ever rotate. The problem is, if these bearings
were a tight knurled, or press fit onto that axle shaft, it might be
easy to keep them from rotating by just not letting the shaft spin.
But, what happens here is that the grease seal is a large
that the wheel spins around....so the seal is on the OD of the bearing
in this case. That's why my stinking seals were so torn when
wheel wobbled. The kicker to the problem is, if you don't
the spacers very tight against the bearing, there's not enough force to
keep the bearing from turning on the shaft. If the bearing
on the axle shaft, then it's becoming USELESS as a bearing.
that point, you're using the aluminum axle as the bushing, and the
wheel is rolling by spinning the hard steel bearing race against your
soft aluminum axle shaft.....instead of turning the roller bearings
inside of the wheel's outer race. The seal itself has a lot
drag against the wheel as it spins, and this drag will make it so that
the wheel tries REALLY hard to make the bearing spin. As it
out, if you don't have tight spacers, it's really easy to get that
bearing spinning. And once the bearing is spinning, the
stuffed right up against it will spin too. And once they
spinning, they'll spin against the fork. If you have the
stainless ones like me, they'll ABSOLUTELY then start carving into your
forks. If you have the new and improved thick aluminum ones
I can't comment firmly on because I haven't seen them), then they would
have more surface area against both the bearing and the fork....so on
one hand the bearing will try to turn it harder, but the fork will
prevent it harder as well. To me, this is STILL going to be
less than ideal situation until you PREVENT the spacers from turning,
and you PROTECT the forks from being worn if they do turn.
lock screws I put in should keep the spacers still. The
will protect the forks. The one further improvement that
be simple would be to drill a tiny hole in the fork on one side, that
drills into the aluminum axle, and then tap for a small hex head
internal setscrew lock, so that you could pin the axle from rotating at
all too. Beyond that, the only real improvement I could
is if you could find a way to either press-fit, or hold that inner
bearing from turning on the axle. Perhaps knurling it, epoxy,
small keyway and shear key, or something like that would be the ticket.
If you've done all of the other steps, and have tight
you probably wouldn't have any huge issues from that point.
The worst thing about it is that no matter what you do, you really
don't have independent control over how tight the bearings are
seated...separate from how tight the axle bolts are and how long the
spacers are. Just to let you know how this all ends up the
have it tonight, the wheel will not continue rolling if you spin it by
hand. I don't think it's too tight from a bearing
but the grease seals against the wheel hub provide a lot of drag, so
they don't let the wheel spin real freely.
A couple other tips, while I'm at it. By the time you get to
hours on your plane, re-check that large nut that holds the fork on.
Mine needed to be tightened almost one full flat to the next
castle stop, to retorque it after it took it's set. I think
spec is about 24lbs. pull of breakout force to rotate the nose at an
The second tip that I can't yet verify is fairing balance. To
prevent shimmy, I've heard that a good idea is to balance your fairing.
Since I had a little lead shot around, and I wanted this all
be perfect now, tonight I weighed out a little lead and taped it to the
nose of the nosewheel fairing. I got it so that I could hold
where it mounts, in the centers of those 4 screw areas, and get it to
be about neutrally balanced. Then I just took a little shot
away, poured the rest into the nose of the fairing, and mixed a couple
of squirts of epoxy. I poured the epoxy into the nose over
shot, put down one layer of cloth, and then a little more epoxy.
By tomorrow that stuff won't be going anywhere, and I already
re-checked the balance and it's now much less tail heavy, so maybe that
will improve things too.
New Axle Parts
Please refer to the
1/20/2009 update HERE
No big news. I'm flying with the above mod right now.
For those wanting to see VANS latest with the axle and spacers
(Update: Matco has MUCH better as of 1/2009),
here are the new parts I got today. The washers are just AN970-6
and AN970-7's. The -6's have the right center hole size, and
work great with the thin stainless spacers. The -7's have a
larger hole, but would have enough O.D. to work perfect with the new
These are the spacers provided from Van's per their Service Bulletins HERE
Here's more info from Mike Lauritzen
from Cleaveland Tools
I just got off the phone with Ken K. the Engineer at Van's and
he enlightened me on how the new parts are to be installed on this nose
First the axle is supposed to be "floating" in between the fork not at
such a length that it is compressed by the fork. I was under the
impression that it was supposed to be just the right length so that
when the spacers were tight against the bearing (causing the bearing to
remain stationary) that the axle would then be tight. I saw something
about using a feeler gauge and sanding the end of the axle. According
to Ken the axle is used to support the bolt and keep the bearings
centered, and it's length should be about 1/16" shorter than the sum of
the other parts when torqued.
Second the entire assembly should be torqued to the torque spec for the
bolt that goes through the fork and axle. He says this seems like a lot
of torque, but Matco says that it is fine for that bearing and it gives
enough pressure for the new spacers to lock on to the bearing. He says
the wheel will be draggy, but that is the way it is supposed to be.
Again at this point the axle will be floating inside the assembly. The
assembly can also be checked simply by re-torqueing during inspection.
This method of adjustment skirts the 'this feels about right' method of
** (Note: Initial reports by Bob Condrey are that this works well)
concepts, maintenance procedures and tips within this site may not be
considered acceptable, and have come from a variety of potentially
unreliable sources. As with any do-it-yourself project,
airplane and doing the maintenance is an "at your own risk"
undertaking. Treat any information you find on this page and
web in general with caution and know that you alone are responsible for
the safety of your airplane, and the maintenance performed.
the ideas posted here were put out with the concept of increased safety
in mind, there are no guarantees. (Hey, it's 2006, what's a
guy to do)