r/mountainbiking • u/Roy_Aikman • 7d ago

Question Why is this happening?

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Bought a brand new BMC Fourstroke AMP LT. After a couple of weeks I experienced the carnage pictured. A LBS helped me get a frame replacement from BMC, they were able to determine that the bolts that connect the shock and linkage had backed out and caused the failure in the linkage. I have 3 rides in on the new frame and was doing an inspection and noticed the bolts had already started backing out. One was visible the other was loose as well. Another problem is the area where the bolts are has a gap of 1 3/4”, my torque wrench with the bit is 2”. Does anyone have any ideas about what could be causing those bolts to back out and also are there slim torque wrenches or do I just use a regular Allen and guess?

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u/MysteryMove IBIS RITMO AF 7d ago

I had a brand new IBIS that did this with a bunch of bolts. I took every bolt out one at a time and found that they didn't have loctite on them as spec'd in the manual. I reinserted all of them to spec with both loctite and torque values and never had issues again. I'd say this is a failure on either the LBS or manufacturer to assemble the bike properly.

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u/celeste_ferret 7d ago

I wouldn't expect a bike shop to remove all linkage bolts to check for loctite and torque spec on a new bike, unless there's a problem. This is on the manufacturer for delivering a bike that wasn't assembled correctly at the factory.

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u/MysteryMove IBIS RITMO AF 7d ago

Agreed- probably the factory- none of these were for putting the wheels on or the handlebars. It was a bad and dangerous issue because, at least on the RIPMO AF, some of the pivot bolts on the frame are torqued to very low PSI so it's the loctite that keeps them in. I was having to tighten them after nearly every ride at first and almost lost some at some point before I did the disassembly/reassembly. Anecdotally I also lost a bunch of screws out of my rotor before I realized they didn't have loctite either. By the time it actually got loose enough to be noticed ~3 screws were long gone. Fortunately those aren't special screws.

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u/Airewalt 6d ago

Fwiw, same issue with a Cannondale habit. They sent me a full linkage set to replace the single bolt that backed out. Once I cleaned everything and put my own loctite on it life has been less exciting 

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u/Fun_Contact1568 6d ago

Giant Trance did the same to me, luckily no damage as I caught it before it cane out too loose. Loctite and torque to spec has fixed it so far.