Need advice - front axle and fork threads stripped

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flyguy
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Need advice - front axle and fork threads stripped

Post by flyguy » Thu Nov 02, 2017 4:48 pm

About a month ago I swapped out my front tire, and two days later something didn't feel right about the front of the bike. When I got home that day, the first pic below is what I saw ... the front wheel was about to come off the bike. The axle had backed out of the fork almost entirely.

As you can see from the photo of the fork and the axle threads, they are all damaged. You can also see at the end of the axle, one of the threads looked like it had been severely damaged, and the "lip" on one of the threads was obviously chewing up the fork threads. I have no idea how or when that happened.

I could move the axle almost all the way into the fully seated position by hand, as the threads on the axle and fork didn't even meet any longer. A new axle would not be a solution, and replacing the axle and the starboard fork would run over $1,000 just for parts.

Luckily, I work at an excellent aviation museum that still flies our planes, and we have a dozen very talented FAA certified mechs who are mostly bikers themselves. The solution one of them had after looking things over is to re-lathe the axle to remove the "chin" on the port side of the axle that limits how far it can go when being screwed in. That will allow the axle to protrude far enough through the fork to rethread it to a smaller thread and put a castellated nut on the outside of the fork to hold it in place more securely than the two tiny set screws on the port fork on the 2013 retro. Fortunately, the axle on this model has tapered threads on it, so letting the axle protrude further into the fork will allow the few "deeper" undamaged threads to engage, and the security of the nut on the outside will act as "belt and suspenders" while also looking much more M70 / Retro / military and "Steam Punk" which is just fine for a Ural!

We are putting this solution into place tonight, so hopefully will be back on the road. IMHO the front axle / fork arrangement on the 2013 retro is far less robust than other models and years that have a whole lot more holding the axle in place, so if your Ural is like mine, you can learn from my issues.

I'd like to hear from some of the experienced folks out there about what you might think of the proposed fix, and if you have any other ideas that might be better?

Thanks to everyone out there on these forums that I've learned so much from in the past four years!
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Re: Need advice - front axle and fork threads stripped

Post by Red Dwarf » Fri Nov 03, 2017 12:23 am

Your repair plan sounds fine.
In a perfect world, you could restore the fork threads with a bronze bushing and keep the axle full size.
Then install new axle or have your aviation mechs build up the damaged threads with new metal and then rethread.

I don't know for sure if the locking action of the outer nut against the fork threads is important but it can't hurt to have it.
Good luck and hopefully your axle setup will soon look like mine. :cheers:

edit: I believe that you should at least install a thin bushing in the fork leg to clean up the damage.
front wheel.jpg
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Re: Need advice - front axle and fork threads stripped

Post by jaybird » Fri Nov 03, 2017 2:10 am

Red Dwarf wrote:Your repair plan sounds fine.
In a perfect world, you could restore the fork threads with a bronze bushing and keep the axle full size.
Then install new axle or have your aviation mechs build up the damaged threads with new metal and then rethread.

I don't know for sure if the locking action of the outer nut against the fork threads is important but it can't hurt to have it.
Good luck and hopefully your axle setup will soon look like mine. :cheers:

edit: I believe that you should at least install a thin bushing in the fork leg to clean up the damage.
front wheel.jpg
How did you wind up with that nut on the outside?

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Re: Need advice - front axle and fork threads stripped

Post by dneprlover » Fri Nov 03, 2017 3:46 am

Common enough ' Ivan ' repair on the older bikes. But they usually machine down a rear spindle to suit.
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Re: Need advice - front axle and fork threads stripped

Post by Tomcatfixer » Fri Nov 03, 2017 4:44 am

Looking forward to images of the remanufactured axle and install.
- Chad

Gordonsville, Virginia, USA

Current rides:
2015 Ural cT "Mobile Chernobyl", 2001 Ural Patrol "Little Red Bear", 1999 Ural Tourist "The RPOC", Mid-Nineties Ural Tourist "The Heap", 1994 Honda VFR750F

Previous rides:
2007 Honda VTR1000 FireStorm (Super Hawk in U.S.)
2001 Buell Blast! - - - - - - - 2005 Yamaha FJR1300
1993 Honda CBR600F2 - -1984 Yamaha FJ1100
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Re: Need advice - front axle and fork threads stripped

Post by flyguy » Fri Nov 03, 2017 9:59 am

Here are the pics from the installed fix. Relathing the axle to move the "lip" that stops the axle from seating past the correct distance allowed around 3/4 inch further travel into the fork. Rethreaded that and put castellated nut on it that comes flush with the end of the axle. Had to go SAE instead of metric on the threads and nut as we couldn't find one the right width in metric to match the length of threaded axle available.

Of course, I lost that same 3/4 inch on the insertion side of the axle, but enough of the tool access hole remains to use it.

Seems to be rock solid on short ride around the block last night. Doing a longer test ride this morning.

We did discuss ways to build up and re-thread the axle and bushing but decided to go simple and more robust. After having seen the threads totally destroyed somehow in under 15,000 km over four years, I like the idea of a nut on the outside instead of relying on two dinky set screws.
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Re: Need advice - front axle and fork threads stripped

Post by Lokiboy » Fri Nov 03, 2017 10:13 am

An excellent modification, Flyguy.

This modification is so common sense you would think from a manufacturing standpoint it would be easier to do than threading the fork as IMZ is currently having to do.
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Re: Need advice - front axle and fork threads stripped

Post by dneprlover » Fri Nov 03, 2017 10:47 am

Lokiboy wrote:An excellent modification, Flyguy.

This modification is so common sense you would think from a manufacturing standpoint it would be easier to do than threading the fork as IMZ is currently having to do.
From an engineering common sense point of view, the L/H thread that Ural use is much better practice. Those threads usually only strip out because of clumsyness ( cross threaded ) or not being tight enough so the spindle rocks and hammers on the thread.

The spindle shouldn't just be snugged up, it should be tight and the rotation of the wheel tends to tighten it up further unless the clamp is pinched up hard as well.

Personally, I feel it failed because it's never been tightened up correctly for a long time.
Last edited by dneprlover on Fri Nov 03, 2017 10:49 am, edited 1 time in total.
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Re: Need advice - front axle and fork threads stripped

Post by gobium » Fri Nov 03, 2017 10:47 am

Question when re thread?
Left or right hand threads?

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Re: Need advice - front axle and fork threads stripped

Post by gobium » Fri Nov 03, 2017 10:54 am

dneprlover wrote:
Lokiboy wrote:An excellent modification, Flyguy.

This modification is so common sense you would think from a manufacturing standpoint it would be easier to do than threading the fork as IMZ is currently having to do.
From an engineering common sense point of view, the L/H thread that Ural use is much better practice. Those threads usually only strip out because of clumsyness ( cross threaded ) or not being tight enough so the spindle rocks and hammers on the thread.

The spindle shouldn't just be snugged up, it should be tight and the rotation of the wheel tends to tighten it up further unless the clamp is pinched up hard as well.

Personally, I feel it failed because it's never been tightened up correctly for a long time.
Are you familiar with new ural retro fork legs and pinch bolt?
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Re: Need advice - front axle and fork threads stripped

Post by dneprlover » Fri Nov 03, 2017 10:59 am

No Gobium, I'm not. What is the difference between those and the millions of other Urals on the road?
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Re: Need advice - front axle and fork threads stripped

Post by gobium » Fri Nov 03, 2017 11:09 am

Pinch bolt is not best designed on retro
If loose, wheel causes axle to over tight and pop the soft fork leg threads

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Re: Need advice - front axle and fork threads stripped

Post by dneprlover » Fri Nov 03, 2017 11:20 am

gobium wrote:Pinch bolt is not best designed on retro
If loose, wheel causes axle to over tight and pop the soft fork leg threads
Good point. One I was not aware of. I have seen loose axles devour threads because they were not tightened up enough but was not aware there is a pinch bolt issue on some newer models. Thank you for the information.
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Re: Need advice - front axle and fork threads stripped

Post by flyguy » Fri Nov 03, 2017 11:39 am

Just out of curiosity about how effective the set screws are in restraining the axle I removed the wheel and simply put the axle in the forks. Cinched the set screws down hard, and then gently tapped the axle with a very small hammer. The axle moved easily. The set screws are just metal-on-metal, not digging into anything.

You would think they would have lathed two channels into the axle so that the set screws could keep the axle from moving, but then no one was expecting the Retro threads to be so easily (pardon the pun) screwed up. Anyway, the current "fix" makes for an easy visual walk-around cue that all is OK. If the Big-A$$ nut is still there on the outside of "Kilroy's" front fork, life is good!

Here's a pic of Kilroy in the new "bike barn" retirement throne room. Cigars, beer fridge, comfy chair, music, and an occasional single malt. On the other side of the door is outdoor kitchen, gas fireplace, head, and pool. I may never see the real house again!
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Re: Need advice - front axle and fork threads stripped

Post by Red Dwarf » Fri Nov 03, 2017 3:17 pm

jaybird wrote:How did you wind up with that nut on the outside?
Apparently that's the way the factory did it in 2012.
Didn't supply a wrench for it, though.
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