Oops. I answered too quickly without noting you quoted John.

When I was young and immortal (and poor), I often rode parts with known cracks, and I definitely would have ridden that stem. I'm with scarlson and rhm , the crack is unlikely to fail catastrophically. But I've turned into a scaredy-cat since I got old and breakable. Knowing it's there would bum me out on high-speed downhills.

Here's a TTT that failed on me when the bike fell over:




Totally different location than OP's crack though.

Mark B

Thanks obuckler for starting this thread. This 3TTT Record was destined for my next build until I took a closer look yesterday. I'm pretty sure this one came on my Italvega Nuovo Record back in 1975.

This was about 40 years ago. It cracked across the clamp; that's all I remember.

I have a 3TTT stem from ~1980 that cracked in the same place a couple years back. I only noticed because it was creaking.

Of course not, my least favourite child gets all the cracked parts.

Huh, seriously considering what that says about me. Recall I got my cracked Cinelli stem from my dad...

EDITORIAL: It never ceases to amaze me how many C&V fans will spend thousands of dollars on a classic bike and CHEAP OUT on a critical item like a stem that can be replaced for $50-$75.... SMH

Yes, verktyg tis I but I would NEVER make a comment like that!

Think of your head as a cantaloupe or maybe a small watermelon or honeydew (honey-do)... Back in the 70's I knew some Docs doing their residencies at several local hospitals. They described making morning rounds in the the neurology wards as "watering the vegetables"! Sad...



Please refer to my first response above.

SAD but very true...

Back in the early 70's when we were young and dumb and everything was trial and error because there was no one around to teach us any better, we (all the local shops) frequently used undersized alloy bars with Cinelli and 3TTT stems.

They were much prettier than the ugly cast aluminum "death stems". Although they were hard to find we could get those forged stems with 22.0mm quills for French and some other European bikes that used metric tubes.

Back then, Cinelli and 3TTT bars were also hard to get plus they were super expensive so we clamped the beautiful Italian forged stems down on 25mm alloy French bars. DOH! After cracking or breaking the clamps on 2-3 stems during assembly, we learned better - the hard way.

Back in 1975 I mounted a Milremo badged internally reinforced 25mm Philippe Professional bar in this 26.4mm Cinelli stem. I used it for over 35 years on at least 3 different bikes that I put a lot of miles on.




One day I realized that the 38cm wide bars were way too narrow for me. When I spread the bar clamp to remove the old bars, the front of it went flying across my workbench with a musical ping!

This break is in a different area but it brings up a point. I suspect that many cracked or broken bar clamps can be traced back to clamping down on undersized bars. Unlike steel which can be repeatedly deformed, aluminum has a much lower capacity for repeated bending before it fails.

Someone gave me this 3TTT stem. On closer examination I saw the cracks in the clamp... Into the junk box!





Here's a Philippe stem with a similar crack:



It appears that some of these cracks may be due to flaws in the forgings but who knows.

I'm always cautious about buying used stems, especially if the clamp needs to be spread. You never know the history of any bike component, especially something as critical as a stem!

verktyg

Dibs on your clamp bolt.

12 years too late... !

verktyg

For the crack of the OP a pretty obvious design flaw looks like the reason for the crack starting - the cone-shaped-with-ridges seat of the nut. And as other examples show similar cracks - what were they thinking?

My EXACT thoughts (that I forgot to mention)....



Old Andrew Agassi Form over Function TV ad.

Like Italian women's 6" spike high heel shoes...



Back when they first came out, I always thought that those 2nd generation 3TTT stems while beautiful, looked a little "light in the loafers" around the neck...



verktyg

I am not familiar with that stem. If the "backer nut" is press fit into the stem, then the issue is not a design flaw as much as a manufacturing quality issue of the boring the hole for the nut (too small). I have not seen the shape of the press fit so can't speculate too much more. Just one more!
The crack is on the peak of the shape as compared to the breaks shown in the follow-up posts which are across or nearly parallel to the bar. This is important because if the break did propagate all the way in the direction of the existing crack, what would fail? The only failure that makes sense to me is that the press fit "nut" would be more likely to rotate. Even then, I don't think it would because of the remaining force around it.
I don't like apparent failed parts or those that might fail any more than the next guy. It just doesn't look good, and it attracts all kinds of opinions, some expressed well and others in an unnecessary sensational way.

I went out and checked 9 of the 11 stems I have with the same clamping design. One was suspect but the loop showed it was a scratch. I will need to file and sand it down to minimize the stress point.

If any Cinelli stem would fail as designed, it would be the 1R. The weak point is right across the middle of the insert. There is a hole for the insert and the thickness of the material is the thinnest around the bar. The wedge pushes the bar against that line but also on either side if the size of the bar is matched to the stem mounting hole.

In the it pays to clean and polish bike parts department, i was polishing up a pre anodized Cinelli stem and saw a crescent shaped black line that would not polish out. was a “crack” well most likely a fault from the original forging.
Time to set aside, bummer as it is a French diameter, not easiest to replace.

In the case of my 3T stem I posted earlier, I was the only owner and it only ever had one set of 3t bars installed,,, once. No repeated opening, no undersized bars.

Mark B

Attractive but fragile. I have one that cracked across the near top of the bar clamp,

It would seem we are on a roll here.

I think it makes a strong case for stress relieving these old souls, they were not really rocket surgery driven in the design or manufacture.

While done fairly well, I think the cutting edge technology of the time was applied sparingly "we know what we're doing, it will be fine".

They really were done very well, few applications where the majority of such parts are still going strong 50-70 years later.

A few minutes with the file and emery cloth would be time well spent.

I'm not joking here, that crack's cause actually eminates from a safety requirement imposed on US-market bike suppliers!

I've seen these failures caused by too wide of a taper on that nut on both Cinelli and 3T forged stems.

The nut was made longer and with a flared taper that got bigger than the hole, so not easily pressed into the hole AT ALL.

The reason for the longer/wider taper was to accommodate an alloy REFLECTOR BRACKET of approximately 3mm thickness, so without said bracket, the tapered nut ends up being forced too far into the lower clamp ear, leading to the ear splitting.

I always check for any sign of such a nut appearing to not fully seat against the rear of the clamp ear, it might be the last red flag given before...

There are a lot of these out there.

Right, right! OK, I'm not crazy. I postulated that earlier, but you probably missed it in the above doomscroll.

Here's mine. Still riding it. And before you ask, yes it looks like that even after I remove the nut. And yes, that's a crummy decaleur poorly brazed on. Bit of a rush job so I'd have a bike to take on my work trip to Michigan. The crack is because of the Arnold Industries lightweight aftermarket nut, which appears to have been the wrong size.

I did miss your posting, even as I had too-quickly scanned the thread for any mention of the reflector bracket.

Perhaps your decaleur's loading also may have contributed to your stem's clamp ear splitting? It somehow never occurred to me that the hole bore was actually tapered.

My first experience with one of these tapered nuts was while tightening a stem, and tightening it some more, wondering why the nut didn't fully seat. I vaguely recall having then removed the nut forcefully and grinding it to a smaller size. The reflector bracket being the issue did not occur to me at that time because I had bought the stem used, without the bracket..

Your cracked stem is now seeing very different force distribution than it was designed around and tested for.
With that crack, I would definitely not ride on it.

The crack was there when my dad gave it to me, which was years ago. Decaleur was added just a couple months back. I also mentioned that above, but it's ok! This thread is a wild one. I actually ground down the nut to make it fit better (no longer spreading the crack) when I was prepping it for brazing the decaleur. In the dark. In the rain. At midnight before my 6am flight.

It appears that on the Cinelli stems, the counterbore is not tapered, but the Arnold Industries nut does have a bit of a taper in this area. I think that's what caused mine.

You are lucky to be so perceptive. I know a hundred guys who would have just blithely cranked it until they cracked it.

I did a little cleanup. A picture was deleted as being in bad taste. A couple posts referring to it were deleted as well - nothing wrong with them but don’t make sense without the deleted image.

Daredevil's some of you are.
That's OK, a man must know their limitations. As I am now full of grey hair, just more conservative.

Trigger Warning:
If carrying groceries, this can happen to your fruit and worse to you body.....please be careful, bad things can happen when equipment fails. Making no light of the dangers or injuries involved.....Best to be safe than sorry.

IMO, It's much better to spend a few dollars on a new stem than risk serious injuries that could last a lifetime....broken bones and lost teeth are not worth it. As others have said would you use it on your child's or best friends bike and feel good about it?
Best, Ben

The horror...

rip Mr. Watermelon