FWIW, the only stem I've ever broken was also a TTT stem. The good news is that I wasn't riding when it happened (bike fell over while I was taking a break). The bad news was that we were on a loaded tour in a very remote area of Michigan's Upper Peninsula.

Back in the 1980's I was riding to work, hit a small bump & hear a crack. *The stem broke, which I think was a 3TTT, but I'm not sure, however the bolt held it together enough that I was able to complete the ride. *Don't remember if I rode it home since it was 30 years ago & I am getting old.

Has anyone seen a crack and caught it before it spread across the face of the stem? At least many people know to look at the base of the crank arm/corner of the spider on Campagnolo Record cranks, and the micro cracks there form fairly slowly. In Sloar's case and the other instances mentioned above, it seems the crack across the stem happens fairly quickly. I assume it would first appear at the edge of the clamp area, but it would be nice to know for sure where to look for the first signs of failure and how much warning one might expect to have.

The testing and quality-control of these parts which assures our safety can't go on for 30 years, except as our final "field testing" at our expense.

Aluminum does have a time-dependent "creep yield" failure mode tendency in tension that steel does not have, so near-infinite life under static tension load depends on an extra measure of designed-in stress reduction (more material) in addition to high levels of processing (i.e. alloying and cold-forging or heat-treatment).

The designers are aware of aluminum's vulnerability to such failure mode, but are designing parts intended to be competitively light.

Such strength/weight performance levels are only realized within a certain time period when parts such as a clamp or a hub flange are subjected to constant tensile stress.
It amazes me that these stem and similar hub-flange failures so often happen when the bike or wheel are sitting unused.

There are no 30-year-old Ksyrium SL wheels out there yet, but the infrequency of failure of their aluminum spokes shows careful design including sophisticated processing of the spoke material.

Most of my vintage stems are of the Cinelli 1A variety. I do have a 3TTT Record stem on my Atala, but it has the same basic form as the Cinelli, with the bolt underneath. I suspect the place most prone to failure would be roughly 180° away from the bolt (highest strain? I'm not an engineer or metallurgist). That puts that spot on top of those stems (where you're more likely to notice it), while for the examples discussed here, that spot is on the front, out of sight while you're riding.

I still think it quite possible that someone tried to clamp a 25.4 bar in a 26.0 stem. The reverse problem wouldn't be possible without a lot of effort.

Back in the early 70's we sold mostly French bikes in the entry level to mid price range models. The better quality Italian bikes that we carried came with Cinelli or 3TTT forged stems plus we sold British and Italian frames.

French size 22mm Cinelli and 3TTT stems were rare as hen's teeth. Standard 22.2mm stems plus Cinelli and 3TTT bars too.

We were young and dumb back then. It was common to fit a wrong sized bar into a stem. Occasionally one of those stems made for a 26.4mm or 26mm bar broke when trying to clamp down on a 25mm or 25.4mm bars.

By the mid 70's common sense, conventional wisdom and experience (bad) and that practice became a no-no among knowledgeable bikies...

Here's a Cinelli 1a stem that that I'd been using since 1975 with 25mm bars. A few years ago I decided to install wider bars with a larger center section. There was a high pitched musical ping as the front of the stem flew off when I gently tried to expand it.



This is a 3TTT Record stem someone gave me on close inspection, I found a bunch of cracks.



The cracks could have resulted from clamping down on an undersize bar or a flaw in the metal called a seam lap or both?

Both of those stems were made of forged aluminum as are the other Cinelli and 3TTT stems mentioned above.

When you buy a used stem, you have no idea of it's history!

It's important to closely inspect a stem - any stem - before using it. Anything that looks odd should be checked with a 10x to 15x loupe or magnifying glass. Closeup pictures with a digital camera can work too.

A few years ago I bought a new Nitto Pearl stem. As I was looking it over, admiring the beautiful finish, I saw something that looked like a scratch. On closer examination I found that it was a crack, either a material or forging flaw.



In their defense Nitto has one of the best reputations for making quality products in the bike industry. Any manufactured products could have unknown defects!

After some searching I found their Japanese website and emailed them pictures with the details.

They got back to me the same day. I received a new replacement stem sent directly to me from Japan the next day.

Nitto even included a prepaid overnight shipping package for returning the defective stem to them so that they could quickly analyze it! They told me that they reinspected all of their inventory.

Have you ever tried to deal with an Italian manufacturer???


To change the subject a little, in the early 70's I had 2 bike boom cast aluminum (death) stems break off while I was test riding customer's bikes, also the top of a steerer on another bike.



I started doing a crude test before getting on any bike that I wasn't familiar with. Holding the bars I subtly lift the front wheel about 2" and bounce it a few times to see if anything feels loose. Over the years I've come across stems, steerers plus fork crowns that were ready to fail.


verktyg

Chas.

Keep in mind, these are/were bicycles and bike components not Swiss watch movements. The street life expectancy for a bicycle was/is about 10 years or less. Most bike and component technologies are market driven with an "Image is everything" attitude (tempered after the fact by lawyers)...

Bike racing is a business to promote something!


verktyg

Chas.

Oh, let's not make excuses for the failure of old parts that have lasted beyond some hypothetical expiration date. These things are old. We get that.

The point I'd like to drive home is that this particular stem has an unusually high failure rate. Lots of guys on this forum are still riding with these, and they should be aware of it. No need for a lawsuit, no need for more exclamation marks, no need for paranoia. But if you're riding a bike with this type of 3ttt stem, keep an eye on it. That's all.