Mornin’
Yesterday afternoon, I was in the middle of a long ride. I started noticing some crunchy “feedback” that could be felt through the cranks as I spun. Didn’t think much of it as I thought probably just needed chain lube (riding lots of dirt and dusty gravel and I ride singlespeed, so I got a couple rides without applying lube). It was bothering me a ton, so I finally stopped and checked out what the heck was going on. Turns out my bottom bracket threads completely sheared from the bottom bracket cup. (Image links below). Thankfully this wasn’t catastrophic, just made for a shitty ride home.
My guess is the cup managed to loosen itself up, and my cranks were acting as a lever to completely crack the interface between the bb cup and threads?
This is the second time I’ve managed to loosen up a right-hand bb cup from Wheels MFG and cause damage. I sort of think it may have to do with these cups not having as much thread engagement as sram gxp/dub, shimano, etc. comparing this cup to a sram gxp cup, there’s about 4-5 less threads.
I’m pretty anal about torquing parts to spec. This was torqued to 25-30 ft lbs as prescribed, using the correct bb cup socket. No spacers in-between the bb shell and frame, so there was maximum engagement of bb threads.
Looking for advice to possibly prevent this in the future? Or maybe others have had similar issues?
I’ll get off my soapbox, thank you all.
https://i.imgur.com/CpVxHge.jpg
by Tommycattt
2 Comments
How old is your frame? It’s possible that you also don’t have great engagement with the threads on the BB cup. Something like Loctite 545 thread sealant may help. Usually, I use antisieze on BB cups, but I have had a FG bike that I had to use 545 on because of shitty BB manufacturing (not saying it’s the case here). Lower tolerances can lead to less than ideal engagement.
This is a consequence of the very low clearance between a 30mm BB spindle and a BSA shell. These cups are simply too thin and are prone to breaking at that stress riser of the last thread. We’ve seen it a few times. This is probably a contributing factor for SRAM going to DUB to get an extra 0.5mm of material into their threaded cups.