Stripped Miyata hub threads

Unicycles and Equipment
1

This sucks. Really sucks.

I went to change the cranks on my Coker yesterday and made the very unfortunate discovery that the threads on the hub had stripped. The hub is DOA. It’s a custom widened Miyata hub by The Unicycle Factory. I’m going to be needing a new hub and a new wheel build for the Coker now. :frowning:

I’m not sure what caused the threads to break off like that. I always use a torque wrench when installing the cranks. I tighten the nut up to 40 foot-pounds. The nut has never been over-torqued. I use a torque wrench in part to make sure that this type of hub failure would never happen.

Some possible factors:

  • I use red high strength Loctite on the threads. Could the Loctite be strong enough to break the threads when removing the nut to change cranks? It has never been difficult to remove the nut using a regular 6 inch socket wrench by hand. I have never measured the torque necessary to break the Loctite bond when removing the nut. I don’t think it’s excessive because it has always been easy enough to remove, but with no torque measurements I can’t know for sure. Maybe using blue medium strength Loctite is a better idea just to be on the safe side.

  • The last cranks on the hub were 170 mm Black Widow Euro cranks. The cranks have always pressed well on the hub tapers. I didn’t realize how far they pressed on the hub tapers till I looked at them while investigating the broken threads. The ends of the tapers in the cranks were right even with the shoulder of the tapers on the hub. In other words the cranks were pressed on as far as the nut would push them on. The nut was at the end of the threads on the hub. Yikes! That’s not good. No more Black Widow Euro’s on Miyata hubs for me. The Black Widow’s just aren’t a match for the tapers on the Miyata hub. This could possibly be a factor in overstressing the threads on the hub.

It is a concern that 40 foot-pounds may not leave a margin of error for stripping or breaking the threads on a Miyata hub. I’m not sure if the red Loctite was a factor or if the poor fitting Black Widow Euro cranks were a factor.

I seem to recall that there may have been a batch of Miyata hubs that was more brittle and prone to failure than normal for the Miyata hub. Can anyone confirm? Is it possible that my hub was made from that batch?

The other side of the hub also has a small chip in the threads that is going to start a bigger failure just like the threads on the other side of the hub. Both sides got the same treatment when installing and removing cranks. Both sides failed at the same time. One side stripped a big chunk of threads while the other side just has a little chip that would grow and probably fail very soon.

My decision now is to decide whether to replace the hub with another widened Miyata hub from The Unicycle Factory or go with the UDC Super-Wide Chromoly Hub. If I go with the TUF widened Miyata hub I may be able to reuse the spokes since the hub will be the same. If I go with the UDC hub I’ll definitely have to get new spokes from The Unicycle Factory and those spokes are expensive.

I have a large high resolution picture of the broken threads in my Miscellaneous Stuff gallery (last photo on the page right now). And I’ll attach a smaller resolution picture here.

Right now I’m going to go try to cheer myself up with a muni ride.

strippedmiyatahubthreads.jpg

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Re: Stripped Miyata hub threads

Sorry to hear about your hub. I felt bad enough when the stud on a
really cheap hub broke. Though there is always that element of
perverse joy in knowing you’re enough of a badass to break things…

Anyway, do you know any machinists that owe you a favor? I’m thinking
you could cut off the studs, then bore and tap holes for use with crank
bolts.

Ken

3

Will the whole wheel fit under a mill?

4

Re: Re: Stripped Miyata hub threads

I did this recently with a stock Coker hub with moderate success; delaced the wheel (noting the position of each spoke), chucked it in a lathe, cut the remaining threads off, and drilled it in the lathe. I was then able to tap it with the special 8mm x 1.0mm “fine” thread tap that bolt-type bicycle spindles use (available from biketoolsetc.com). The wheel hasn’t been ridden yet, so I’m not sure how it is going to hold up. My concern is that it IS possible to do this with the cheaper hubs (like the stock Coker hub) because the metal is soft, but the results won’t last because the metal is soft. With a higher-quality hub the spindle may be hard enough that it is difficult or just plain impossible to tap.

5

I have one that looks exactly like that on a Sueze hub on my secondary Muni. I got mine used and don’t know the history of it. I was able to drill out the crank so the nut could go down onto the lower few threads as a temporary fix. I’m currently looking for a used splined hub or might just go with a UDC. Mine looked as though it was loctited. I wonder if that is a problem?

6

John,

I have a widened Suzue here that someone gave me, with the same stripped thread problem. I don’t know how it was treated as far as torque, Locktitie, etc. so can’t speculate much on why it stripped. I plan to attempt to repair it, but haven’t decided which approach yet, and have been too busy with other things to do it. As for cutting the stud off and drilling and tapping, the shaft seems to be very hard as it did not mark with a file. That being the case it would probably have to be annealed to do the repair, then re-tempered to get the strength back.
I think a more practical fix may be to TIG weld just enough material onto the threads to be able to file it back to the proper OD and re-thread it with a die. This could possibly be done without breaking down the wheel build, and the heat should be low enough and concentrated enough to not ruin the temper of the rest of the hub. Using heat sink clay or clamping aluminum bars to the square taper can help save the temper also.
Considering the cost involved in replacing the hub, it may be worth attempting it, and all you have to lose is what the welder charges.

I will go ahead and attempt the fix on this hub and let you know how it goes. That is better than experimenting on your built wheel.

As for the Locktite, I completely understand why people use it but… It is my thinking that on something where you will be disassembling it regularly (like I do to swap cranks) OR will be re-torgueing regularly to take up looseness (as in square taper “settling in”) that you are better off with antiseize on the threads.

Scott

7

With the Loctite I never re-torque the crank nuts just to see if they’re still tight. I leave them be. They stay tight and stay in place. I’ve also never had a loose crank since Loctiting the crank nuts. Tighten once and let them be.

I don’t change the cranks on the Coker very often. Most of the time I keep the 140’s on it. A few times during the year I’ll swap to the 170’s and leave them on for a while then switch back to the 140’s.

The broken threads are actually where the nut is when I’m using the 140’s. With the 170’s the nut is bottomed out on the threads. Maybe there is something about the 140 mm cranks that caused problems. They’re old steel 140’s from my old Schwinn.

The Suzue hubs are hardened quite well. It’s not going to be machinable while it’s hardened. That hardness is also what makes the threads so brittle. If the hub didn’t get hardened correctly it could cause the threads to be more brittle than they should be. There’s a lot of variables in heat treating and no guarantee that it will always happen to the desired properties.

My current plan right now is to unbuild the wheel and carefully mark each spoke where it was in the hub. That way if I get the hub repaired or get another widened Suzue I’ll be able to put the old spokes on in the same relative locations. I’m still undecided whether to go with another TUF hub or go with the UDC hub.

On the plus side, the muni ride was great. I only thought about my broken Coker hub a few times during the ride and that was only because I was trying not to think about it. I had one of my fastest rides up the climb and passed four bikes going up. They weren’t the most fit cyclists (mom, dad, and two kids) but they did get a good head start on me.

8

We tryed putting black widows on my coker. It didnt work at all. Their holes are to big I guess and just go right down the taper. It was hard to not make them hit the frame. We just gave up on them.

I use the super wide UDC hub. I like it a lot. I used to have the stock guy on there I think the suzue I wasnt a fan of. I was able to use the same spokes too. The rebuild really isnt that hard. Just get a friend to put the nipples on and work from the hub and you got it spoked in no time. Trueing it isnt even that hard either.

9

Have you tried the Black Widows on the UDC hub or were you using the stock hub at the time?

The problem with using the old spokes on a UDC hub is that the spokes have already been stressed and bent to fit the geometry of The Uunicycle Factory widened Miyata hub. Even though the UDC hub will take the same length of spokes the UDC hub will not have the same geometry and the same shape and angle of the spoke holes. The old spokes would not be happy in a different hub. The spokes may break due to the new stress.

10

Brilliant!

11

Re: Stripped Miyata hub threads

I have had this happen to three square taper hubs in the past 4 or 5 months. The first to go was the Suzue hub in my muni, closely followed by the Suzue hub in my freestyle uni. These hubs were almost the same age and lasted three years with a lot of use. I came to the conclusion that the Suzue had reached the ends of their lifetimes and had gotten old and worn out.

That conclusion changed when the same thing happened to my 29er’s hub. This hub was a prototype UDC hub, less than a year old and hadn’t had much use. I now believe the biggest cause in the failure of these hubs was the way I mounted cranks on them. Instead of using a mallet to seat the crank on the taper, I used a pedal/crank tool to torque up the crank nut. I believe this unnecessarily stressed the axle threads and contributed to their failure. The moral of the story is to use your mallet, folks!

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Re: Re: Stripped Miyata hub threads

Tony Melton using a mallet.

mallet.jpeg

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Sorry to hear about your hub, John.

It sounds as though the combination of red loctite and ill-fitting cranks did the trick. Red loctite is designed to be a permanent fixing and removed with heating with a blowtorch. In addition, the assembly is not designed to have the nut pushing against a fixed hard obstacle like the end of the threads. A properly fitting assembly will involve a tight, yet somewhat flexible connection that allows the connection to “breathe”, as it were, under stress. In your scenario, there was no give-and-take in the threads, so I surmise that the forces probably exceeded the 40 ft-lbs considerably. Proper assembly and component choice removes most of the problems associated with this type of hub. In your case, it sounds like the Black Widows are proving not to be a good choice for unicycling cranks. Thanks for the information. Although I did not in your case, I, for one, will not recommend them to future customers.

Otherwise, it sounds like your practice of torquing on the crank to spec was the proper approach and a good habit. Don’t abandon that!

The widened Suzue hub is the best wide hub currently available, in my humble opinion. It has a thicker hollow axle and carefully tuned bearing surfaces. It isn’t powder-coated, which makes any developing rust immediately evident, and treatable. With proper treatment the hub will last a long time. And it has been extensively tested under extreme conditions.

Of course, under these conditions, some are bound to fail. 24 hour off-road racing is an extreme condition for any cycling component. One of the top area mountain bike racers being serviced by our bike shop would bring his bike in after every weekend race for a tune-up and component replacement.

The UDC hub seems to be a reasonable lower-cost alternative. A close look will show rough workmanship, poorly machined spoke holes, and an odd bearing size. Moreover, it is powder-coated, and has shown to hide rust that can compromise the unit’s strength. Yet the hub is substantially less in cost. The customer’s riding needs and budget should determine the choice of hub.

Other, better, designs are in the works, and hopefully someday we will see them on the market. Until then, what we have now is still far better than what we had five years ago.

LiveWire customers will find that, should they follow the correct mounting procedures , their wheel is warranteed for this type of damage.

14

As an experiment I removed the cranks from my freestyle uni that has a Miyata (Suzue) hub. The crank nuts had been put on using red high strength Loctite. I used the torque wrench to remove the nuts to measure how much torque it took to break the red Loctite bond. It took less than 15 foot-pounds of torque to break the red Loctite bond. It was difficult to get an exact measurement. My best estimate is that it was somewhere between 10 to 15 foot-pounds to break the Loctite bond on each of the nuts.

I cleaned everything up and then installed the cranks again using blue medium strength Loctite this time and only went to 35 foot-pounds of torque on the nuts. I’ll see how well the freestyle cranks stay tight.

It takes less than 15 foot-pounds of torque to break the nut free. I don’t see that as a problem. The threads are coarse which means the Loctite doesn’t get as strong of a bond as it would with the same size of nut with tight fitting fine pitch threads. I’m not ready to call the red Loctite a causal factor but I’m still going to switch to blue medium strength Loctite just to be on the safe side just in case.

15

it’s late, i’m tired and have been up for far too long, but all i got out of that last post was

it takes 15 ft lbs of torque to break john’s nuts free…

hahahah.

ps sorry to hear about the hub. i’ve super strong epoxied my nimbus X crank to my suzue hub on my muni. i tore the threads out doing trials on it. (i was dumb and didn’t have a trials uni yet). so far that hub has held up pretty well to some good drops/muni-ing. no more trials though. the second epoxy job worked much better.

16

In swapping a set of stock Lasco cranks on my Coker for a set of PDC’s very nifty adjustable Kookas, I found the thread on the RHS stripped in almost exactly the same manner as John discovered (which lead to his original post - see his attached photo). John, what did you end up doing to repair or replace this? There were a few suggestions in this thread but I couldn’t find the eventual winner. It seems like there’s a range of options, from trying to repair the exisiting unit to replacing the entire wheelset. I’m considering making this an excuse to replace the stock wheelset with the UDC Airfoil upgrade. (Dave Stockton’s lovely wheel would be great, but hard to justify given the amount & kind of riding.) I’d be grateful for advice from anyone who’s had a similar problem - what sort of fix worked for you?

Many thanks!
Doug

strippedmiyatahubthreads.jpg

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Doug, I think the best long term fix is just getting a UDC super wide hub. They are only $30. I think the bolt holding on the crank is a better design than a nut. If the threads were ever damaged, hopefully the internal threading in the hub is harder than the bolt threads. You could simply get a new bolt, or possibly retap the internal threads. The wheel build really isn’t that bad to do yourself (with some help from Sheldon Brown’s tutorial), and you can use the same stock spokes. When I did my first wheel build I was surprised how easily it went. Of course if you have the extra cash, an Airfoil rim is a nice item. Not necessary though if you’re only doing road riding and not running brakes.

Hope this helps.

-Phil

18

When I saw this thread bumped I had a bad feeling that someone else had suffered the same fate. It’s unfortunate when a hub dies, and even more so when it’s a custom hub from The Unicycle Factory (as it was in my case).

I replaced my stripped hub with a UDC extra-wide hub. That meant getting the wheel rebuilt. The UDC hub has been doing very well and it’s a great fit with the PDC adjustable Kooka’s. The old hub is no more.

The UDC hub will be much less likely to suffer stripped or damaged threads. The threads are better machined and there are more threads engaged with the bolt than there are with the nut on the Miyata style hubs.

The good news is that UDC now carries quality Coker spokes so you can get a new set of 14-gauge SS spokes along with the UDC extra-wide hub and Airfoil rim.

I’m curious, did you have any Loctite on the hub threads when they stripped? I’ve been wondering if somehow the red (high strength) Loctite threadlocker I was using contributed to the threads getting damaged. In any event, I’m now using the medium strength Loctite on the crank threads and not the red high strength stuff.

19

Phil, John,

Thank you both for your excellent advice. I will go with the UDC extra-wide hub, 14-gauge SS spokes and Airfoil rim, methinks. This was the first time the original cranks had been off. I didn’t see any Loctite anywhere, so in this case at least that wasn’t a contributing factor.

Doug

20

While you’re paying the shipping, you might consider getting 2 hubs (they’re so cheap). Then you can build a spare stock wheel for an extra $30 instead of ending up with worthless spokes and rim.