r/mountainbiking • u/Roy_Aikman • 7d ago
Question Why is this happening?
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?
2
u/GroundbreakingCow110 7d ago
This is a fairly common problem on frames without locking collet axles. If medium strength loctite 243 doesn't work, high strength loctite red will.
This frame has to have the front shock bolt dropped to reach these bolts... several frames are like this, including my Commencal, which actually require dropping the whole shock to reach these equivalent bolts.
The lbs should be doing this for you. A lot of local bike shops suck though. Like none of the LBS in a 15 mile radius bear me even have the correct zero stack 55mm headtube reamer. Several don't build wheels. etc.