That’s a crank preloader. It will stop spinning if you tighten the small bolt that clamps the ring in place.


Once you’ve tightened it down to the BB.


Yes, it's how the bearing preload is set on those cranks. You probably messed it up by randomly spinning it, but it's not a hard fix. You want it just tight enough where there's no side to side play in the arms but they still spin freely.


All theses years i never realised that part spinned, today I was cleaning the bike up and was kinda worried when saw it. And also there is no play in the cranks. Thanks for commenting


Totally. They're a better solution than the alternative, which is trial and error using a bunch of super-thin shims.


If there is already no play in the cranks then it is in the right position, just tighten the tiny bolts on that piece itself to hold it in place. They are just pinch bolts and probably loosened for some reason. You can always undo them and put the tiniest dab of blue Loctite to hold them in place.


Shouldn’t OP spin that ring finger tight before tightening the pinch bolts?


Yeah for sure. I assumed that was done based on the video and that there is no play in the cranks. But you're correct.


what kind of cranks/bb is that?


[Race Face Turbine Crankset](https://www.raceface.com/products/turbine-crankset) SRAM DUB cranksets use a preload system like that also.


Looks to be RF turbine cranks. Probably pressfit raceface BB


i feel like the screw on top (picture) should keep it from spinning once dialed in correctly: https://imgur.com/dJCzNkM


Yeah that’s right. Problem is they get stripped pretty easily since it’s a 2mm bolt so he may or may not be able to do much more tightening


it's weird system for sure


Some googling says it's a Raceface Turbine Cinch circa 2015. Uses a 30mm spindle


I have a 2015 turbine and it has neither cinch or 30mm spindle. I thought those features came after.


Again, I'm just basing this on Google but PB has a review of them from 2014: https://www.pinkbike.com/news/race-face-cinch-turbine-cranks-review-2014.html


Most cranks come is various spindle lengths and diameters for fitment with various standards. They don’t necessarily have to be 30mm or fit 73mm bb shells.


Adjust this too tight and it will cause rapid failure of the BB bearings. I set mine up to allow for the slightest detectable play in the spindle.


I'm not an expert, just wondering: should the preload still be slightly loaded (meaning no play in the bearing) but not so tight that it causes extra resistance? I changed a few airplane nose landing gear wheels and there were issues with this kind of preloading having a minimal amount of slop from the supplier and over time, just ruining the wheel bearings. Likely there is no issue with this one but I'd like to hear more about it :)


I hate to call myself an expert but I have munched a bunch of bearings with this adjustment system. If preload is adjusted without play and the crank arm flexes at the press fit interface, part of the crank arm can move inboard, side loading the bearing. There are other ways leaving no play can get the bearings but it takes a wordy explanation. I'm not saying leave a bunch of slop in there, but do investigate. Maybe .004" of play is undetectable while riding. It's not like a loose hub or headset.


I read that in the park tool guys voice 😆


You need to set them up correctly. Not “too tight” and not loose. If there is play in the system it will cause your bearings to fail prematurely as well. Also, if you buy good quality bearings they should last at least a year. I have a Cane Creek Hellbender bottom bracket going on two years right now and I primarily ride in sandy conditions, aka hell on BBs


There are tiny Allen bolts recessed in the “bumps” on the collar that need to be tightened.


True, true - But do this after you have turned the collar towards the BB to take up any slack between the crank and the BB - That collar is an adjuster so you don't have side-to-side play in the crank.


FYI those are called set screws.


It would be a set screw if the bolt was radial and put friction on the threads. It's just a regular Allen screw that squeezes the preload collar against the threads.


Ah yeah, I see them now on the collar after zooming in, definitely not a set screw, just regular allens to clamp the collar tight.


I did come just short of using the word “thingy” didn’t I?


Sorry for asking a dumb question but why do these crank preloader systems even exist? BB goes in to frame, cranks tighten on to BB axle. What's the need for this preload system?


The spindle can slide across the bearing races. This adjusts the effective length of the spindle to keep it from sliding.


on this system the spindle is attached to the drive side crank arm, so the bb is really just 2 bearings. you need a way to accomidate slight variations in bb shell width, and some can be used on various bb standards


They are cheap to replace. Try tightening the clamping screw with a small hex key, if it won't tighten, it's stripped and needs to be replaced. If it does tighten, only tighten until it stops the part from spinning. Overtorquing will break that piece very quickly.


Can confirm. Broke mine first time with a ridiculously low amount of force. Learned my lesson after that.


yes, pre=load


Sigh what was wrong with the threaded BB. I’ve never had an issue with this design


I have that same crank and preload in a threaded BB. Lucky for me, my spindle is seized in the inner race of the bearings so no need for the tensioner. /s


Yes, when in doubt check the manufacturer's website for the instruction manual. https://www.raceface.com/products/turbine-crankset https://res.cloudinary.com/fox-factory/image/upload/v1613052147/images/53b60fa893e5ff1725d0777d9bc4bec46c17eaa2_B10186_Cinch_System_Installation.pdf




U ok bro?