I have a Miyata Deluxe unicycle, about a year old, that is beginning
to have some mechanical problems I’m not sure how to fix. It broke a
couple spokes after a particularly disgraceful dismount on the
basketball court, and I fixed those, but I also noticed that the wheel
isn’t held firmly by the fork. On either side, I can pull on the fork
with my hand and it’ll move about a centimeter, exposing the bearing.
That alone wouldn’t bother me, but the wheel is also coming out of
alignment. When the uni receives lateral stress (like when I’m idling,
which at this point is almost always with the right foot down), the
tire starts to rub against the inside of the fork. (There’s not a lot
of clearance on the Miyata Deluxe). Usually I have to bang it back
towards the center, and it’ll stay there until the next time I try to
hop a curb or something.
I took a look at the mechanism and I don’t really see how it’s
supposed to work. The bearing holders only cup the bearing casings on
the outside, so they only appear to keep the fork from flexing inwards,
not outwards. I didn’t see anything obvious I could tighten or adjust
to change the behavior.
It sounds like your bearings are slipping on the hub. This has happened to several of my unis too. The bearings are just press fit on the hub and sometimes that press fit works itself loose. When this happens I pull the bearings off the hub, use Loctite high strength sleeve retainer, and then press the bearings back on. The Loctite will keep the bearings from slipping on the hub. Even though it is “high strength” you’ll still be able to remove the bearings with a standard bearing puller and hand tools.
Loctite sleeve retainer is designed to secure press fit parts. You can find it at better stocked auto supply stores. The OEM number for the sleeve retainer is 64000 or 640. Loctite also makes special stuff for bearing mounts. The part number for this stuff is 68035, but I have not been able to find this stuff in stores. The sleeve retainer is easier to find.
You may also want to take this opportunity to replace the bearings with new ones if you think the slippage has damaged the inner race of the bearings.
When pressing the bearings back on the hub make sure to only put force on the inner race of the bearing. Avoid pressing on the bearing seal or outer race because that could damage the bearing. I use a short piece of pipe or a deep well socket that is the same diameter as the inner race to press the bearing on.
No, I don’t think this is it. When I pull one of the fork blades by hand,
the bearing stays where it’s supposed to be–it’s just the fork blade, and
the bearing holder, which pull off. I can see the bearing when I pull
the fork blade.
)Loctite sleeve retainer is designed to secure press fit parts. You can
)find it at better stocked auto supply stores. The OEM number for the
)sleeve retainer is 64000 or 640. Loctite also makes special stuff for
)bearing mounts. The part number for this stuff is 68035, but I have not
)been able to find this stuff in stores. The sleeve retainer is easier
)to find.
That might work in between the bearing and the bearing holder, too.
I’ll check it out.
-Tom
Oh, now I see. I don’t have any experience with the Miyata bearing holders so I don’t know what might work to keep the bearing in the holder. If you can’t fix your existing bearing holder, unicycle.com does sell replacement Miyata bearings/mounts. But they’re $22 per pair. http://www.unicycle.com/shopping/shopexd.asp?id=143
If the bearings are press fit in the Miyata bearing mount then Loctite just might do the trick.
Is it possible that the bearing did slip closer to the axel, lodged in the new position and will not move easly from the new position? This would allow for the bearing holder slop and bearing movement. If the bearing holders are afixed to the frame properly and the frame has not deformed… well what else could it be? I can put MUCH more force on the bearings as I ride and torque the wheel around than I can with my hand, checking the placement…
It’s great to see that unicycle.com now stocks Loctite.
Remember to always determine if a primer is needed. Many of the Loctite
grades won’t cure without being exposed to an active metal. If one of the
components is: non-metallic, stainless, zinc plated, etc. then the Loctite
won’t achieve much strength. The primer has some kind of active metal in it
with a solvent carrier.
We use Primer N or T.
Let the solvent evaporate off and then assemble. Solvents can damage some
plastics(composites) and rubber, so be cautious.
Loctite has a good website with technical data sheets of each product.
Although I may have preached this stuff before, it is due to a very costly
experience with uncured Loctite leaching out of stainless components to an
area where it was unwelcome. Loctite isn’t just for quick fix scenarios, it
can be a vital component of a well designed machine (unicycle).
It is a press fit. I took everything apart, cleaned everything off,
added some grease and tapped the holders back onto the bearings. It
seemed to work for a short ride–we’ll see if it survives basketball
today. If not I’ll probably grab soe Loctite. Thanks for the advice.
-Tom
In article <rhysling.xwua@timelimit.unicyclist.com>,
rhysling <rhysling.xwua@timelimit.unicyclist.com> wrote:
)
)Tom Holub wrote:
)>
)> No, I don’t think this is it. When I pull one of the fork blades by
)> hand,
)> the bearing stays where it’s supposed to be–it’s just the fork blade,
)> and
)> the bearing holder, which pull off. I can see the bearing when I
)> pull
)> the fork blade.
)> *
)
)Is it possible that the bearing did slip closer to the axel, lodged in
)the new position and will not move easly from the new position? This
)would allow for the bearing holder slop and bearing movement. If the
)bearing holders are afixed to the frame properly and the frame has not
)deformed… well what else could it be? I can put MUCH more force on
)the bearings as I ride and torque the wheel around than I can with my
)hand, checking the placement…
It’s certainly possible the bearings have moved, but their positioning
seems symmetrical. It’s also possible that both crept in the same amount,
but I don’t think that’s likely. I might just have messed up the
press-fit seal somehow. (Too much curb hopping).
Have you noticed that doing tricks badly puts more stress on the unicycle
than doing them well? That’s probably my problem right there.
I must say, working on this thing is rather cumbersome compared to a bike.
I have to remove the pedals to take the cranks off (the pedals interfere
with my crank extractor), and remove the cranks to deal with the bearings.
The four bolts that hold the bearing holders are also problematic; after
a few cycles of installing and removing, three of the four were
stripped to some extent. And you have to install and remove just to
change a tube. Is there any progress on quick-release bearing holders?
-Tom
It would surprise me if there were not bearing shoulders on the axle that prevent the bearings from moving inward. Especially on a quality unicycle like a Miyata. It must be the clamps. The “partially” stripped threads on the clamp bolts already sound suspicious.