Boom Cracked at Handlebar clamp While Climbing

[ak-tux]

Today, while I was climbing a hill on my S40, I heard a rhythmic clicking sound in sync with my left foot. I thought it was my wheel. Stopped and checked and wheel was fine. Spokes , derailluer, brake all was clear. I hopped back on and the sound momentarily disappeared but came back when I put power. It completely disappeared as I descended back home.

As I parked my bike I suddenly noticed the new crack on the boom at the handlebar clamp area. The clamps are evenly tightened with equal gap spacing on all the four bolts. (I think I once checked with a torque wrench and it was 5Nm or there about.) I have only had one minor fall on this bike more than a year ago and it was to my right side as I slid on a sandy patch on the road. This crack is on the left. A couple of years back it also once fell on the derailuer side while I was opening my gate. So this crack seems to me like a result of repeated rythmic stress while pedalling.

The area of the crack is perfectly in line with the push pull forces of pedalling the MBB. I suspect others may have experienced this?

I feel very sad. I have grown to love this bike. According to strava, I have logged 16,138 Km on this bike in 2 and half years. I have fine tuned the fit to near perfection, modified the seat padding to minimize eliminate the recumbutt. It has truly become a joy to ride. It's a sad day for me.

Its an S40 model 2019.
(It had a front disk brake but the original front wheel freehub started to sieze. I had spare rimbrake wheel so I changed the front to a Tektro rim brake. )

 

[Frito Bandito]

It is aluminum, so is it possible to have an aluminum welder weld it? Or do you plan to buy another boom?

 

[Robert Holler]

Give us an email as we can get you a new slider.

 

[Beano]

It is aluminum, so is it possible to have an aluminum welder weld it? Or do you plan to buy another boom?

Welding Aluminum is more difficult than you think, it's not like welding steel.

 

[Frito Bandito]

Welding Aluminum is more difficult than you think, it's not like welding steel.

A slider is probably cheaper than having a welder fill the crack, but I don't know if Ak-tux knows a good welder who can do that inexpensively.

 

[ak-tux]

It is aluminum, so is it possible to have an aluminum welder weld it? Or do you plan to buy another boom?

My only fear is that welding aluminium is a lot more delicate than steel. If not done properly it can result in an even weaker joint on an already high stress area. I think it needs TIG or MIG which have don't have access to at the moment. I also read that 7xxx grade series aluminium alloys welds should/can be heat-treated to strengthen it to avoid cracking at the welds.

In short, Iam not sure it would be safe unless it's done by a profesional welder. I will research on that. I don't want to end up with the handlebar yanked away from the boom in the middle of a sprint!

My homemade MBB was a steel frame. I could easily get a gas welder to make make my modifications and any repairs.

 

[Frito Bandito]

No worries. Looks like you can get a new slider fairly easily so you shouldn't be down for long

 

[ak-tux]

No worries. Looks like you can get a new slider fairly easily so you shouldn't be down for long

Thanks. I will religate it to the trainer for now. (I got a used Cycleops fluid2 that works well for my S40.) I think it's safe enough indoors on a stationary trainer in this case. No risk of crashing incase the handlebar comes loose.

For the outdoors, I will go back to my homemade MBB for some time.

 

[ak-tux]

After this incident, I couldn't help but think if it was possible to redesign the end of the boom to make the handlebar clamp area a replaceable zero offset Oversized stem that screws in or clamps to the end. It might add some few extra grams but it make is easier and cheaper to replace. It will also make it easer to put an offset instead of having a curved slider option.

Food for thought.






or

 

[chicorider]

Definitely contact Robert Holler at Cruzbike. He has helped me with parts needs more than once. It sounds like he can set you up with a replacement.

 

[Always-Learnin]

ak-tuk...

Looking for a S40/Q45/V20 Straight Boom Slider

Hello out there, if anyone recently upgraded to a curved slider and may be having the original Straight Slider that they don't need, kindly inbox me. It will be local USA shipping to Texas. I estimate that to be about $20, I'd like to replace one on my S40 which developed a crack at the...

forum.cruzbike.com

Boom is on the way...

 

[ak-tux]

ak-tuk...

Looking for a S40/Q45/V20 Straight Boom Slider

Hello out there, if anyone recently upgraded to a curved slider and may be having the original Straight Slider that they don't need, kindly inbox me. It will be local USA shipping to Texas. I estimate that to be about $20, I'd like to replace one on my S40 which developed a crack at the...

forum.cruzbike.com

Boom is on the way...

Boom received!

 

[Always-Learnin]

Boom received!

Awesome!!!

 

[ak-tux]

She is back on the road!

Thanks @Always-Learnin Jim, for the Boom. It fits perfectly.

 

[Always-Learnin]

She is back on the road!

Thanks @Always-Learnin Jim, for the Boom. It fits perfectly.

View attachment 15055

Hallelujah!!!

 

[macg4d1g]

Gorgeous S40, AK! Love the red accents with the black and gray. So glad you're up and running again. I just got an S40 as my first Cruzbike. In fact, you commented on a progress post I made. Thanks for posting this thread. There's a lot of peaky hills where I live and, at 185 lbs, I'm pulling hard when I climb. I'll keep an eye on that clamp.

 

[Bill Wightman]

Glad you are back up and running. From hindsight you will notice that threads runs right through the middle of the crack, the crack started near a transition from thick material to thin material, and lastly the fitting weld is very close. So the weld heat affected zone possibly slightly weakens the local aluminum heat treat levels, the thick-to-thin transition at the bolt creates a stress riser, and the female thread root at (30 degrees) is probably where the crack actually initiates (thread root lines up perfectly with the crack). Metal fatigue is a sneaky little problem.

 

[Tuloose]

View attachment 14860

I cracked the handlebar clamp on my V20 in the same place. These clamps aren't very sturdy.

 

[ak-tux]

Oh sorry!
After I got the replacement boom, I was very carefull to ensure not to exceed 5Nm evenly on the 4 bolts. I used a torque wrench this time. No guess work. I pray and hope it never happens again.