What did you do TO / WITH / FOR your bike today!

Fred Nurk

No custom title here
Took the chain off to isolate the cranks and it is indeed the crankset that's the cause of the bumping feeling! The 8mm hex bolt was a bit loose but even with tightening it was still bumping a bit.

If I spin the crank arms 180 degrees then push down on both arms, I feel the bump (how the fuck do you describe a really short movement?). Spin again and rest, same bump.

I wonder if the bearing pre-loader could do with some tightening? Other than that or using the seatpost breaker to really tighten up the cranks, I'm out of ideas.
Did you use the correct amount ot spacers on the BB?
Did you tighten the BB up correctly prior to installing the cranks?
As per the RaceFace install for other cranks, the test for a correctly installed crank is generally as shown... https://res.cloudinary.com/fox-fact...fect_Cinch_Installation_Web___Copy_og8odi.pdf
Despite all the different methods of crank attachment, the play ends up being the same if they're loose.

There's only one place for the play to develop unless the cranks are really fucked, and that's at the connection. Don't lean on the pedals to check crank play...
 

Rorschach

Didnt pay $250 for this custom title
It was more using a bearing on something with such a miniscule amount of rotation that had me surprised. I would've expected IGUS bushings or somesuch...
True. I hear it works pretty well though for such a simple system.
 

Cardy George

Piercing rural members since 1981
They act a pivot for the seatpost don't they? Similar to the Kingpin on the Cannondale Topstone
Topstone Carbon | Gravel Bikes | Cannondale
Kinda, sorta, but no. The flex point is actually down at the seat tube/bb junction, so up where the bearings are it doesn't pivot so much as slide. The rest of the frame is rigid. My guess is the little black tube bears weight and rotates inside the seat tube as it flexes and the bearings allow that more easily.

Either way, it's a very effective system for what I deal with 99% of the time.

And it's the first time I've broken a pivot, Mr Beebenson, last time I cracked the frame.
 
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