Cracked front axle

[pago cruiser]

Have been trying to get my WASP Leading Axle forks installed for the last couple weeks, and work keeps conspiring to steal my wrenching time.   Had the LL's on the bike a couple weekends ago, and this afternoon got back on the project to pull the front wheel off and re-engineer the caliper mounts - but that's another story.

The WASP stuff fits tight; as in you have to tap the axle into the bearings - with a hammer.  A little too tight a fit, but that's also another story.

Tapped the WASP axle almost out, and needed to use the VALK axle to tap it out the other side.  Picked it up, tapped it out, dropped the axle, pulled the wheel, took a sip of beer and ... the thought occurred: why did my thumb feel a sharp ridge on the VALK axle?

Dang. I have been riding 50 years, wrenching for most of that, and have never, ever, seen or heard of a stock axle  - hollow or solid - failure on a street bike.

   

The crack line starts on the left in the pic, then works its way up and at angle to the point where the large diameter part that rides in the fork slider boss meets the axle diameter - about 90 degrees from crack start to finish.  While stress risers at rapid transitions are typical failure points - still... a LOT of bikes have this axle design...

Dang.

[Savago]

Nice photo and thanks for sharing this report.

Any theory on *why* it happened?

[RDKLL]

Hmmm, is it possible it could be from over-tightening over the years? Great find and something I will pay mor attention to the next time I take the front wheel off.
Starts between MO and MS and goes to NV
Any more update on the wing-valk project.

No motorcycle riding for me until very late in July but I would still like to ride down and look at it first hand

[Skinhead]

Was that axle from a wrecked bike, or one that had front end damage by any chance?

[The emperor has no clothes]

I would suspect its from using it to punch out the other axle.

[pago cruiser]

Here's another pic of the crack where it wraps around:



It almost hits larger diameter end, but stops about 0.10" shy.  I'm going to find some dye penetrant this week to highlight this for a photo.

About the wrecked bike, don't know, but I don't think so; the bike came from a local bike shop, 36,000 miles on it.  But neither the fork bottoms nor the axle ends are buggered.

Overtightening - maybe.  But I would think that over-tightening the axle bolt would strip the threads before material failure.  I would certainly hope this is the designed-in failure mode.

EDIT - replying to this as it was added during my post  - In using one axle to punch/beat through/tap the other one out - steel should not fail under these low impacts.  I's not as if I was using a 5lb sledge, swinging mightily, multiple times.  Rather, a 1 lb mallet tapping from maybe 6" away, with the other axles moving 1/2"-1" each time.  I generally use a 3/8" socket extension, but did not have enough lengths handy.   

My theory (thought about this a lot last night) is overloading/over-stressing.

The stock VALK is about 750 lbs with a full tank of gas, at about a 50% front-rear weight distribution. With a Motorvation F2 steel frame, sidecar body, battery, air horn/compressor, tools, spares, gear for a week trip, canine, and wife, we are prolly real close to 1200-1300 lbs. Albeit spread over 3 wheels.  

Combine that with:
1. A 6 degree rake to the triples in order to make the VALK steer a bit better due to the hack, and
2. A 1.5" fork extensions to make up for the height lost due to the triple tree rake, and
3. A really rough hard pack washboard and potholed 3 mile driveway, that I usually deal with by speed.  I can ride it at a walking speed, taking an hour to go three miles; or at about 40-45 mph, providing a relative smooth ride, but which works because it is too fast for the forks to respond to the rough road, thereby transferring the rapid loads/unloads to the "hard parts" of the bike.  Like axles and bearings.

With all the above, I think it just overloaded the hollow axle.  A hollow axle is typically a good design on a motorcycle.  Without getting into a "which oil is best" discussion, a hollow axle, when compared to a solid of same diameter, provides good weight savings, with little loss of strength.  

BUT.  It also changes the failure mode.  A solid axle will bend before failure.  A hollow axle cracks, as the load carrying outer diameter does not have a solid core to help absorb forces.  It has almost the same load carrying ability, but has lost its toughness, for lack of a better word.

Not a good failure mode on a part that is difficult to visually inspect on a regular basis.  Just what is the inspection interval on an axle???

All that said, on some machining forums I visited last night, JAP axle material is generally not highly regarded.  Other materials (4130/4140, etc) are much stronger and tougher.   The VALK LL's from WASP came with their own axle - I have an email to them to see what material they use, as their axle is about 2" longer than the VALK stock axle.

I'll post this over on the Sidecar.com forum, as there are some HACK manufacturers over there who have way more experience.  I'll update this as I learn more.

[Tfrank59]

that's more than a little scary.  hope mine's not cracked--I haven't done a penetrant dye test but maybe will from now on!  I know you can get a replacement on evilbay for around $20--hopefully it's not also cracked!

[old2soon]

Wunder How Much of a "fudge factor" is designed into those axles? Going to W.V. last year what ever space was left over in my trailer was given over to haulin my Brothers "stuff" he had for sale. On a detour we hit a nasty gravely steep stretch of road on a down hill. Forks were working a Lot. Haven't done a dye penetrant test since the Navy. Like to see the results of the dye penetrant test when available.  Thanks for the heads up!  RIDE SAFE.

[indybobm]

Could have been a defect when originally made. You might never know.

[Tfrank59]

Well I have to believe that Honda would not have passed that defective part through QC, but it could happen. Axles are normally 4140 heat treated with tempering which keeps them from being too brittle.  Assuming it wasn't cracked at assembly it was just probably not drawn back quite enough.

[pago cruiser]

"Any more update on the wing-valk project."

It's still a project, but got pre-empted by a re-roof on the house, a motorhome purchase, then major systems upgrade (months and months),  bought and brought back to life a DT175 ring-dinger for the bumper, then a month long x-country trip.  Then had a hip replaced (months and months of tough mobility), then a  local shop closed and I had to get my long term project with them home, and have been working on that (XS650 Tracker/Enduro) for a few months).  Then wifey wanted to take the Hack to Minny Soda in July, so am now working on the leading links; which came with buggered caliper mounts necessitating a re-design, which led to the discovery of the cracked axle...

So.  Life is good... I actually had to pull the triple trees off the WingValk frame in order to put stock trees back on the Hack. So it's gone from an almost roller, to sitting on blocks at both ends...   soon, I hope. 

If anyone is interested in a set of 6 degree trees, I'll have some posted for sale eventually...

[mrgeoff]

If the axle was cracked, what would be the symptom that one would draw a conclusion to, that they had a cracked axle, without ever seeing it first...??? would the wheel wobble, fall off, steer funny...??? Just asking...!!! I don't think you would really know until you pulled the wheel off...!!!

[Tfrank59]

I can jump in and speak to this because I work as a machinist in equipment repair. A cracked axle really isn't anything but an accident waiting to happen. There are no problems until it fully fails and then it's catastrophic obviously if the axle breaks in two.  (and I suppose with the pinch bolts on our Forks an axle could break in two and the wheel could still remain on the motorcycle long enough to come to a stop)  but that's why I said above that it's really scary because I don't want to be riding aound with that potential on such a critical part. On that Point you are correct -- you really wouldn't know (short of the axle actually breaking and the Wheel potentially falling off) until you pull the wheel off to check it, which is also why I said I'm going to be doing a Dye penetrant test on my axles whenever I have the wheels pulled

[mrgeoff]

Thanks...!!!