Unexplained stem failure (Thomson-w/pics)

Nov 1, 20 14:14

Post #1 of 35 (5012 views)

Can anyone speculate on what might have caused the failure of the faceplate of my stem?

The stem was first installed in January 2016 as part of a new bike build. I installed a new bar in 2018, and I haven't fiddled with it since. The clamp-ons use the Redshift QR attachment hardware, but I have the Profile Design T3+ extensions and F-35 armrests.

I had been riding regularly up until I contracted COVID in late September. A couple weeks later, I tried riding a short distance around the neighborhood to see if I was recovered enough to start riding again, but no, so I put the bike back on the stand.

Fast forward two weeks and I thought I'd try again, but as soon as I tried to ride out of the driveway, the bars slipped badly. The stem faceplate had split sometime during that two weeks. Is this type of failure unheard of?

Of course, I'm also wondering if I should replace the X2 faceplate (available from Thomson for a reasonable charge), or replace the entire stem. That would be more expensive, and require a trip to the LBS to properly adjust the headset - and typically a long wait for the LBS to get the work done.

◼︎ We shall soon be in a world in which a man may be howled down for saying that two and two make four, in which people will persecute the heresy of calling a triangle a three-sided figure, and hang a man for maddening a mob with the news that grass is green. - Chesterton

Re: Unexplained stem failure (Thomson-w/pics) [TMI] [ In reply to ]

Nov 1, 20 14:28

Post #2 of 35 (4994 views)

It’s not unheard of, but the Thompson doesn’t have a whole lot of material on the face plate, so what is there will be subject to higher loads.

I’d replace the stem. It’s dead easy, just tighten the top cap first, go slowly until you “just” eliminate all the play, then tighten the pinch bolts. Super easy.

A reliable stem is pretty cheap.

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Re: Unexplained stem failure (Thomson-w/pics) [ In reply to ]

Nov 1, 20 14:40

Post #3 of 35 (4979 views)

I had been looking at the Profile Design 1/Seventeen line of stems, but couldn't find any info on them in this forum.

◼︎ We shall soon be in a world in which a man may be howled down for saying that two and two make four, in which people will persecute the heresy of calling a triangle a three-sided figure, and hang a man for maddening a mob with the news that grass is green. - Chesterton

Re: Unexplained stem failure (Thomson-w/pics) [TMI] [ In reply to ]

Nov 1, 20 14:53

Post #4 of 35 (4960 views)

Why would you need to go to a bike shop?

Re: Unexplained stem failure (Thomson-w/pics) [TMI] [ In reply to ]

Nov 1, 20 14:54

Post #5 of 35 (4958 views)

The failure is localized, personally I'd just replace the faceplate unless there is visible damage elsewhere.

Figuring out the cause would require closer inspection, but here are some possibilities:

-Over-torqued (it appears to have broken at the highest stress point on the plate).

-Stress concentration due to a small defect during the forging process or subsequent machining. This led to a small crack that propagated across the plate.

-Corrosion. This does not look to be the case, looking at the crack and the general condition of the surrounding hardware.

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Re: Unexplained stem failure (Thomson-w/pics) [TMI] [ In reply to ]

Nov 1, 20 14:58

Post #6 of 35 (4951 views)

not at all an uncommon failure point on Thomson stems; usually an overtorque issue but also if proper and equal gap not maintained top to bottom of faceplate.

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Re: Unexplained stem failure (Thomson-w/pics) [ABarnes] [ In reply to ]

Nov 1, 20 15:08

Post #7 of 35 (4933 views)

"...but also if proper and equal gap not maintained top to bottom of faceplate."
This is a really important point.
Along with tightening in a couple of stages. Otherwise the loads aren't evenly distributed and the face plate gets extra bending across the front (where it broke).

I had a face plate crack on a machined stem a couple of years back - 4 bolt plate and having taken it on and off multiple times over years, eventually one corner of the plate cracked where it was a little thinner than elsewhere.

I'd just swap the face plate myself unless you think you've damaged the stem body eg in a crash.
The fact they are available separately tells you a lot!

Re: Unexplained stem failure (Thomson-w/pics) [ In reply to ]

Nov 1, 20 18:42

Post #8 of 35 (4830 views)

No crash involved. I used an automotive feeler gauge to make sure that the gaps were equal.

However, I absolutely could not keep the bars from rotating with the recommended torque. Whether cleaned with alcohol, coated with grease, or with carbon paste applied, the bars would slip. I am sure that they were torqued above 6 Nm.

I already have a new bar in the parts box that I intended to install, but it has a similar smooth finish that is just as likely to need a higher than recommended torque to avoid slipping.

Of course, I could be doing it wrong.

◼︎ We shall soon be in a world in which a man may be howled down for saying that two and two make four, in which people will persecute the heresy of calling a triangle a three-sided figure, and hang a man for maddening a mob with the news that grass is green. - Chesterton

Re: Unexplained stem failure (Thomson-w/pics) [TMI] [ In reply to ]

Nov 1, 20 19:02

Post #9 of 35 (4807 views)

I don't know if your.faceplate is carbon but even if it is not, that is the one area.on the bike I strongly feel you have to use a torque wrench. If you go carbon it is an absolute must since all 4 screws should share the same load.

If you replace this yourself, and yes it's very easy,.do it with a torque wrench.

Also carbon paste is required.for this area. The risk of slippage is too high to not use it.

Last edited by: lightheir: Nov 1, 20 19:03

Re: Unexplained stem failure (Thomson-w/pics) [TMI] [ In reply to ]

Nov 1, 20 19:07

Post #10 of 35 (4800 views)

TMI wrote:

I already have a new bar in the parts box that I intended to install, but it has a similar smooth finish that is just as likely to need a higher than recommended torque to avoid slipping.

You previously said that in order to replace the stem, you would have to take your bike to the LBS to have them adjust the headset. If you can complete the full re-cable that is necessary to swap bars, you can learn to adjust your own headset. Not trying to demean or talk down to you. Just encouraging you to learn a new valuable skill since.

Re: Unexplained stem failure (Thomson-w/pics) [lightheir] [ In reply to ]

Nov 1, 20 19:22

Post #11 of 35 (4782 views)

Thomson doesn't make carbon faceplates.

Re: Unexplained stem failure (Thomson-w/pics) [TMI] [ In reply to ]

Nov 1, 20 19:27

Post #12 of 35 (4775 views)

If that’s the case, just replace it. I highly recommend the Uno ultralight range of stem. They are stiff, light (~100g/90mm), but most importantly, the installation process is far better (bottom out top bolts, torque bottom bolts). Never had a problem with them slipping or biting into handlebars.

https://www.ebay.ca/itm/193721309489

TMI wrote:

No crash involved. I used an automotive feeler gauge to make sure that the gaps were equal.

However, I absolutely could not keep the bars from rotating with the recommended torque. Whether cleaned with alcohol, coated with grease, or with carbon paste applied, the bars would slip. I am sure that they were torqued above 6 Nm.

I already have a new bar in the parts box that I intended to install, but it has a similar smooth finish that is just as likely to need a higher than recommended torque to avoid slipping.

Of course, I could be doing it wrong.

Re: Unexplained stem failure (Thomson-w/pics) [ In reply to ]

Nov 1, 20 19:45

Post #13 of 35 (4758 views)

Yeah, the bars and stem are all aluminum.

The only threadless stem I've tried to work on actually had a starnut that wasn't properly secured. I'm confident my current frame should be able to be adjusted like I've seen in various videos.

Changing a faceplate is easier than changing the whole stem, as long as I can get the torque to hold.

◼︎ We shall soon be in a world in which a man may be howled down for saying that two and two make four, in which people will persecute the heresy of calling a triangle a three-sided figure, and hang a man for maddening a mob with the news that grass is green. - Chesterton

Re: Unexplained stem failure (Thomson-w/pics) [beston] [ In reply to ]

Nov 1, 20 20:23

Post #14 of 35 (4739 views)

beston wrote:

If that’s the case, just replace it. I highly recommend the Uno ultralight range of stem. They are stiff, light (~100g/90mm), but most importantly, the installation process is far better (bottom out top bolts, torque bottom bolts). Never had a problem with them slipping or biting into handlebars.

https://www.ebay.ca/itm/193721309489

TMI wrote:

No crash involved. I used an automotive feeler gauge to make sure that the gaps were equal.

However, I absolutely could not keep the bars from rotating with the recommended torque. Whether cleaned with alcohol, coated with grease, or with carbon paste applied, the bars would slip. I am sure that they were torqued above 6 Nm.

I already have a new bar in the parts box that I intended to install, but it has a similar smooth finish that is just as likely to need a higher than recommended torque to avoid slipping.

Of course, I could be doing it wrong.

+1

I use the Kalloy UNO stems on many of my bikes. Light, cheap...and as mentioned the bolt tightening system works great. The one upgrade I do is to swap out the bolts for stainless versions. I also use carbon assembly paste, even with Al bars.

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Depression, Neurocognitive problems, Dementias (Testing and Evaluation), Trauma and PTSD, Traumatic Brain Injury (TBI)

Re: Unexplained stem failure (Thomson-w/pics) [TMI] [ In reply to ]

Nov 1, 20 23:40

Post #15 of 35 (4668 views)

TMI wrote:

No crash involved. I used an automotive feeler gauge to make sure that the gaps were equal.

However, I absolutely could not keep the bars from rotating with the recommended torque. Whether cleaned with alcohol, coated with grease, or with carbon paste applied, the bars would slip. I am sure that they were torqued above 6 Nm.

I already have a new bar in the parts box that I intended to install, but it has a similar smooth finish that is just as likely to need a higher than recommended torque to avoid slipping.

Of course, I could be doing it wrong.

Logic would tell me the design of the stem and using tri bars with extensions was a recipe for disaster. Four bolts spread to each corner would but a more even force across the complete section of the bar being clamped. With the two bolts the force wont be as even across the area. With a standard road bar you won’t have the same leverage trying to rotate the bars and you most likely would have gotten away with the designed torque. I am sure a four bolt faceplate clamp will be much more effective at designed torque with tri bars.

Re: Unexplained stem failure (Thomson-w/pics) [Shambolic] [ In reply to ]

Nov 2, 20 7:16

Post #16 of 35 (4509 views)

A quick look at your picture and it is obvious that the aerobars are way overtorqued.
Far enough that I would recommend handlebar replacement and new bolts as they are now quite bent.
There is only one person to blame in this scenario.

Re: Unexplained stem failure (Thomson-w/pics) [lyrrad] [ In reply to ]

Nov 2, 20 7:35

Post #17 of 35 (4485 views)

lyrrad wrote:

A quick look at your picture and it is obvious that the aerobars are way overtorqued.
Far enough that I would recommend handlebar replacement and new bolts as they are now quite bent.
There is only one person to blame in this scenario.

How can you tell by looking at the picture?

Re: Unexplained stem failure (Thomson-w/pics) [Titanflexr] [ In reply to ]

Nov 2, 20 10:25

Post #18 of 35 (4418 views)

Titanflexr wrote:

\ The one upgrade I do is to swap out the bolts for stainless versions.

I actually really like the bolts that come with the higher end stems (Still only $20-$30). I find they don't rust/corrode easily (or at all). Not sure if you're using a better grade of SS though.

Not sure why these stems aren't more popular as they're I think they are a genuine improvement over most handlebar clamping mechanisms!

Re: Unexplained stem failure (Thomson-w/pics) [TMI] [ In reply to ]

Nov 2, 20 10:54

Post #19 of 35 (4399 views)

Quote:

However, I absolutely could not keep the bars from rotating with the recommended torque. Whether cleaned with alcohol, coated with grease, or with carbon paste applied, the bars would slip. I am sure that they were torqued above 6 Nm.

It might be a good idea to measure the actual diameter of your bars. I wouldn't be surprised if they were a bit undersized. This could explain both the break in the faceplate and the inability to keep the bars from moving.
IME, this stem design doesn't work super well with bars that are on the low side of the nominal diameter window.

Tech writer/support on this here site. FIST school instructor and certified bike fitter. Formerly at Diamondback Bikes, LeMond Fitness, FSA, TiCycles, etc.
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Re: Unexplained stem failure (Thomson-w/pics) [TMI] [ In reply to ]

Nov 2, 20 14:31

Post #20 of 35 (4309 views)

Just get an FSA omega stem from amazon - since you're using an FSA omega handlebar. They're like $30 and are rock solid. The Uno stems that someone else has recommended in this thread are also a solid choice.

Next races on the schedule: none at the moment

Re: Unexplained stem failure (Thomson-w/pics) [alex_korr] [ In reply to ]

Nov 2, 20 19:30

Post #21 of 35 (4241 views)

Quote:

It might be a good idea to measure the actual diameter of your bars. I wouldn't be surprised if they were a bit undersized. This could explain both the break in the faceplate and the inability to keep the bars from moving.
IME, this stem design doesn't work super well with bars that are on the low side of the nominal diameter window.

I may be able to borrow a micrometer from work. I have a DEDA bar that is labeled as 31.7mm, but I had been led to believe that was simply an alternative metric conversion and was the same as 1-1/4" (31.75mm)

I may simply buy a new bar and stem. It's been a while since I bought any new gear, so maybe it's time.

alex_korr wrote:

Just get an FSA omega stem from amazon - since you're using an FSA omega handlebar. They're like $30 and are rock solid. The Uno stems that someone else has recommended in this thread are also a solid choice.

It's likely the bar is compromised, too, and it's three seasons old; I usually replace aluminum bars every two seasons. I am surprised at all the UNO recommendations. Even with a 4-bolt design, there's not much more clamping material than the Thomson stem. And I usually avoid any ultralight components.

Whatever I go with, I'll need a -17°/130.

◼︎ We shall soon be in a world in which a man may be howled down for saying that two and two make four, in which people will persecute the heresy of calling a triangle a three-sided figure, and hang a man for maddening a mob with the news that grass is green. - Chesterton

Re: Unexplained stem failure (Thomson-w/pics) [TMI] [ In reply to ]

Nov 2, 20 19:53

Post #22 of 35 (4226 views)

I had that happen on a very old Thomson, gave them a call and they replaced it no questions asked.

Re: Unexplained stem failure (Thomson-w/pics) [TMI] [ In reply to ]

Nov 2, 20 20:21

Post #23 of 35 (4209 views)

Quote:

I have a DEDA bar that is labeled as 31.7mm, but I had been led to believe that was simply an alternative metric conversion and was the same as 1-1/4" (31.75mm)

That's the rub. It *is* a conversion from 1 1/4", and some manufacturers (Deda) round down to 31.7, most others round up to 31.8. Some vary across different products in their line.

If you get a slightly undersized 31.7 bar and a slightly oversized 31.8 stem you can have problems. Ditto, if you have a stem design that really wants to see 31.8, it can be a problem if you're putting 31.7 in it.

Tech writer/support on this here site. FIST school instructor and certified bike fitter. Formerly at Diamondback Bikes, LeMond Fitness, FSA, TiCycles, etc.
Coaching and bike fit - http://source-e.net/ Cyclocross blog - https://crosssports.net/ BJJ instruction - https://ballardbjj.com/

Re: Unexplained stem failure (Thomson-w/pics) [TMI] [ In reply to ]

Nov 2, 20 23:52

Post #24 of 35 (4178 views)

TMI wrote:

However, I absolutely could not keep the bars from rotating with the recommended torque. Whether cleaned with alcohol, coated with grease, or with carbon paste applied, the bars would slip. I am sure that they were torqued above 6 Nm.

Ha ha maybe you should change the thread title now that you've answered your own question??? Yes it broke from being overtorqued, and yes it's common on that design when you overtorque it (on other brands too). You could probably just replace the faceplate and install it properly and be fine. You could also buy a four-bolt stem and that might help solve your slippage problem. Installing a stem is simple and should not require help from your LBS.

Re: Unexplained stem failure (Thomson-w/pics) [TMI] [ In reply to ]

Nov 3, 20 3:20

Post #25 of 35 (4148 views)

I have this issue with my current gravel bike. The bars clearly state 31.8 mm clamp diameter but they must be slightly smaller due to tolerance issues. I have tried a couple of stems and some work a bit better than others but all of them required over-torquing to get a stable attachment. What I have ultimately done is wrap the clamping area in electric tape. This shims out the bar a bit and provides a surface for the stem to bite into. It would require a bit more effort to due this for the stem and aero bars but it will reduce the torque necessary to stabilize the system.

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