Part failure - steering stem

Discoloration on the stem seems it cracked another time and the last time was the final straw. 

That’s crazy…ever come loose? I don’t think that should be a concern while riding dirt bikes but it sucks that it is. 

Fingers crossed you didn't crash, or came away without injury. This is absolutely terrifying. I've never seen a break like that, but I wonder if it was over tightened at some point. 

How are you alive!!?  

Didnt Varize or someone snap theirs a few years ago?  

that didn’t just happen in one day of riding, I would say lack of pre ride checks and regular maintenance.

Overtightened - Not likely, a castellated nut, generally tightened by a relatively small C Spanner, or even a bloke with a punch and a hammer, I very much doubt would  stress a steer tube, unless it was garbage metal, or had a machining fault that created a stress riser. 

I'd contact Ride Engineering, from the get go, about this failure .

I would recommend taking it to an Engineer / Machinist and let them diagnose if there was any 'fault' with the machining. Sharpe / non radiused finishing at that break point might be identifiable. That's the sort of thing that can lead to such a failure .

Of course, some Monumental 'Hit'(s) at some time in the  last 2 years of using it, may well be a factor.

By the OP's Not mentioning injury, he's got away rather well from such a major failure.  

I'm glad he's OK. 

Frightening Stuff!

If it was overtightened, you would have noticed it steering a lot harder from too much pressure on the bearings: the poor man's steering damper.

Sometime crap happens. Like mentioned above, a stress riser in the original that wasn't able to be visually seen. These are dirt bikes, not fighter jets. They aren't doing NDT on every part before assembly. Random parts pulled l for QA/QC sure, but not all of them. Even then, if damage isn't directly visible I'm sure it moves on to assembly.

Hmmm, that’s a scary one…

Did you have any big crashes prior to this? It is clear it cracked previously, then fatigued over time till it broke through completely just recently. But what caused that is the question… Stems in general don’t see a lot of stress unless something is out of whack. Over-tightening the bearing won’t do it. It’s much bigger than that. 

Two things come to mind:

1) It was a bad design and a crack initiated then grew through till it broke. If this were the situation, we’d hear about it a lot more than once. I haven’t heard of this as a problem from any manufacturer, so that’s unlikely. Or perhaps it was a weird one-off machining issue where there was an unintentional stress riser, which started a crack and it eventually grew through and broke. Possible, but not terribly likely with proven CNC programs and a reputable machine shop making the parts. Or there was a localized defect in the material. Possible, but unless they sourced garbage material, highly unlikely.

2) You had a previous crash that was big enough to bend the stem. Note that crash big enough means force big enough, which you may be surprised how little of a crash that can take if all things happen at the right (worst) angle. It doesn’t necessarily mean a huge crash. If you keep riding with a bent stem, it goes through a stress cycle every time you turn the bars, which adds up quick and causes a crack to propagate and eventually crack through under a big enough load

We’ve seen this once before on out parts for reason #2. The rider had a big crash that bent the stem and they kept riding on it and it eventually broke. We got the stem back, put it between two v-blocks on the bearing diameters and it had a runout (bend) of more than 1mm(!). Every time they turned the bars, it went through a full, and rather significant, stress reversal, which is a recipe for fatigue failure.

I can’t tell from just photos, but I bet this is option two. As much as I hate to stick up for Ride “Engineering”, from my best guess I doubt they are at fault here. Likely just an earlier crash with damage that went unnoticed and fatigue did its thing. A bit of a freak thing, but it happens. Get a hold of them and see if they’ll relace the stem for you. Tell Adrian In stuck up for him and maybe he’ll be surprised enough to make it happen. 😂

Those stearing stems should not break.

I've been close to MX for 46 years both as a racer and a professional mechanic and I have never seen a break like that.

I'm guessing that came from the production line with a fault in the material @Luxon MX 

Luxon may solve this mystery for us.

My bad lol. I just saw Luxon's post now. Still got to read his reply.

Look how thick the profile is at the point of failure- it’s like 12mm. How does a tube that thick break in half?

No way that’s caused by even temporary over-tightening. You could put 150 FT/LBS of torque on that stem. The threads would strip but the stem wouldn’t break like that.

Fatigue crack, starting where the thread meets the bearing diameter.  You can see the discoloration in the front part of the break, looks like it failed totally when that got to the bore in the centre. The thread should ideally run out into an undercut to relieve the spike point, where the thread finishes. 

This is why you check stuff. 

Even a rattle can spray would find that crack early. 

I’ve never seen a break like that without hitting something head on. Luxon is probably spot on with some previous damage that over time caused this. I’ve used Ride clamps before and if memory serves me they come with the stem installed. I’ve bought others where you press out the stock stem and use it. It could have also been just a freak case of bad material with the grain wrong and turned the wrong way just enough to cause the perfect storm. 

O’Mara snapped an aluminum stem on his works Suzuki back in 89 Anaheim SX in think….probably didn’t help his confidence …..sometimes when I ride my Evo..90”s bikes I think about something like this happening….is that a stock stem or came with aftermarket clamps? 

Decoster at a Trans AMA . After that, he, I think, never wore anything other than a full face helmet

Tony DiStefano at a SX.

I guess it was Omara, as you say sandman768. I knew there was at least three spectacular failures for Suzuki over a bit of time.

Robgvx , I think, was at the Dutch GP - Lierop I think -  where Jobes Kawasaki lost its front end - though, I think it was the Welded Triple Clamps that failed.

Langston had a front end break off at a SX, didn't he?

Things Break - but basic machining ( and materials ) Ef Ups - as hinted at by philG, - can really , Really Bite you.

Just as an aside, when I fitted WPCCs to my CRE, I decided to keep the OEM bearing set from the 500. (I'd probably use a  later model CRF Top bearing, with a sleeve like I describe later, if I were to do it now - I've an extra set of triple clamps to do so if I wanted )  that necessitated machining down the the top bearing landing on the steer tube, to take the smaller ID bearing ( I think it went from 29mm, to 26mm? ) and I made damned sure that No Stress raisers were made. Of course, I had to do an insert for the Top Triple clamp to match the new , smaller OD of the top of the steer tube, and Every 'edge', had No 'edge'. I also, press fitted a round bar of 7075 into the steer tube from the top of the ST, to 25mm below the bearing contact. Over Kill, basically. The bottom bearing, required a sleeve, as the Honda one was 1mm  bigger than to OD of the Steer tube at the bottom. Things can be done, but you've Got To DO IT properly.

Here's the bits I made ( minus the lower bearing sleeve ) to fit the WP front end, and take the 20mm CR axle and wheel - that sleeve at the top opposite the top nut, is the sleeve to re-match the top triple to the machined Steer Tube :

Oh, and the Steer stops on the lowers to match the CR frame stop - you can spot the  sleeve above the bearing to enable the use of the lower CR bearing :

Sorry for commandeering this, but I'm a bit of a Mad Scientist, in my rather basic workshop, at times. And, I guess, overly proud of what I can do. 

What material would that stem be made of? 

Possible bad material pair (ex: stainless-aluminum), crack initiated from a location of galvanic corrosion? 

Possible chemical corrosion crack-fatigue initiated by chlorinated brake cleaner? 

When people snap bolts, they always snap at the end of the thread, because that is where the biggest stress raiser is. 

I looked at @Luxon MX 's website, and he has a lovely pic of a stem showing just how the thread runs into the undercut, to prevent this, the only thing you have to do is make sure that the radius of the undercut isnt too small, or its a sharp corner because that is where everything will break, if it does.  In Aerospace we get more issues with sharp corners, rads, blends and mismatched than with anything dimensional, because that is always where cracks start. 

The other thing to know, is that Hard Anodising can also give issues, while  it improves the wear resistance of the base material greatly, it also causes microcracking in the surface of the material, so be careful where you apply that.  

When it broke, did the top clamp separate from the fork upon landing and the entire front end fell out of the bike? Or did the bike relatively stay together and felt really weird?

I swear I’m ordering Luxon clamps one day. Everything he posts on here is gold.

I have every part luxon makes on my 24 yz450f and his customer service is top notch,  nothing against ride engineering but now is your chance.

can you help me learn? what is an undercut? is that where the final thread drops off into an extended area of a small diameter before there's a shoulder leading to a larger dia?

You want the threads to run out into an undercut, which is a relief smaller in diameter than the thread minor diameter. Shown with the green arrows here:

without the undercut, the threads end at the full diameter, which creates a stress riser and a recipe for fatigue failure (red arrows below).

Billy always with the deep and very clear responses. You’re good people buddy 

Wasn't it Club MX that were breaking clamps or was it the stem?

AH ok thank you. that's excellent. i think i've seen that in AR barrels. 

Neither. We had two sets of KTM clamps break 3+ years ago due to the KTM pinch bolt design on the stem. Every other manufacturer has had the same failures as well. You can read all about that here: https://www.luxonmx.com/blog-luxon-broken-triple-clamps-failure.html

Our Gen3 clamps eliminated the pinch bolt design on KTM/Husky/GasGas and Beta brands and uses the more robust Japanese style steering stem design which eliminated the issue.