Mechanic Question - BB related

[cuda]

what would cause a spindle to come loose in the BB shell?

I picked up a bike (on) Friday from the shop. I had a new Wheels Mfg threaded PF BB installed and a new crank (Easton cinch)

Yesterday after a 20mi moderately aggressive test ride I noticed that the spider rings were loose. I took it back and asked for him to check the spacers and tighten things up.

Today I took a relatively mellow flattish gravel ride but upped the tempo on the pavement segments to put some stress on the cranks to make sure everything was good to go for a longer ride. At about 20miles into the ride the spindle developed side to side play. So now I'm a having a *** moment?

There is now 3-5mm of play in the spindle and I have a gouge in the paint from the small chainring.

What caused this?

[bikinchris]

I've not seen a Bike Friday with a PF bottom bracket.
Unless the bearings are shot already, it has to have come loose.

[cuda]

I've not seen a Bike Friday with a PF bottom bracket.
Unless the bearings are shot already, it has to have come loose.

sorry, I should have written "on" Friday. thanks. I suck.


anyhow the BB is a threaded PF and is still tight in the cups. Yeah, maybe the bearings are defective.

thanks

[DavidC]

Those cinch cranks have a preload adjuster on the non-drive side. It's possible the crank was not installed with proper preload adjustment.

I haven't used a Cinch crank before, but that preload adjuster seems identical to SRAM's system. The process should be:
1. Install spindle into bottom bracket
2. Attach drive side crank arm and tighten bolt
3. Gently tap with a soft hammer onto the bolt area of the drive side. This will fully push the crankset to the non-drive side. I.e. if there's any play in the system it is shifted to the non-drive side.
4. Loosen the set screw on the preload adjuster and tighten by hand, then retighten set screw. (On SRAM there's an arrow on the adjuster for which way to turn it. I'm guessing Easton will have that too.) Don't tighten preload adjuster very hard at all! And don't tighten the set screw too tight either.

You can do this yourself now, no need to go to shop. Just need a rubber mallet or other soft hammer and a hex wrench for the set screw. (You're not hitting hard with the hammer at all, so you could even use a normal hammer and a piece of wood held against crankset to not damage it.) Just be sure to add in step 0: loosen preload adjuster set screw and fully loosen preload adjuster.

Found this. This guy shows you how it's done.
https://youtu.be/VnQHVwGy81g?t=690

[slowpoke]

To be clear, the crank arms are both tight and still on, but the spindle still has lateral play?

DavidC's instructions are pretty much all there, minus adding the required dust caps and spacers. Could the mechanic have forgotten to add them?

The Race Face installation instructions are very clear here: https://youtu.be/iNEel-bLAc8?t=409

[muz]

The fact that you have the small ring contacting the frame tells me that you don't have enough spacers, at least on the drive side. The pre-load ring can only make up for a couple mm of play. You need to have 30mm spacers to take up the rest of the slack. The bottom bracket and the spacers have to be 92.6mm +/- 1mm.

Check out the Cinch bottom bracket installation here (https://cdn.shopify.com/s/files/1/0061/9216/9050/files/Cinch_System_Installation.pdf?62296).

[DavidC]

The fact that you have the small ring contacting the frame tells me that you don't have enough spacers, at least on the drive side. The pre-load ring can only make up for a couple mm of play. You need to have 30mm spacers to take up the rest of the slack. The bottom bracket and the spacers have to be 92.6mm +/- 1mm.

Very good point!

[dddd]

Even though the spindle isn't normally a press-fit in the bearings, often on a particular combination of bb and crank there is the need to use a mallet to move the right crankarm inward to fully meet the bearings.

If this is needed but the crank wasn't fully seated "hammered" against the driveside bearing, then in use the crank may have shifted inward and ended up with the huge amount of freeplay.
Had the crank been fully seated, then the left arm, spacer(s), preload adjuster, together, would have prevented any movement that might allow the crank to move in either direction.
So it sounds like an initially-tight "press fit" of the spindle in the bearings somehow loosened from the stresses of those 20 miles.

Where there is plastic shim material between the spindle and bearings, the initially-tight fit and subsequent freeing-up of the spindle fit would be normal, which would manifest as the poorly-seated crank now free to move side to side.