The Shiny New AM831 Group Buy (A) Thread!

[scourge]

It is worth showing the link assembly issues with pictures rather than just words to get the message better across, so I've drawn some (not to scale, dimensions exaggerated, showing the principles).

This is the 831 assembly of the upper link to one of the rear triangle eyelets, as far as I could make it out. Grey is the aluminum link, black the carbon triangle, blue the ball bearing and pink the screw. The screw presses the inner race of the bearing against the link, so the screw and inner race are one piece with the link. There is some clearance between the screw head and the triangle so that the parts can rotate with respect to each other.





This assembly would be alright if the two eyelets of the triangle (only one shown) were perfectly rigid relative to each other, but that is not the case. So, what prevents the outer bearing from sliding out of the triangle eyelet (to the left) is in practice only the press force of the outer bearing race in the eyelet, as Maffly stated.

Inevitably, when the triangle is submitted to lateral forces, the bearing will end up sliding to this position, where the eyelet contacts the screw head, and rubs against it as the triangle and link rotate relative to each other. After a while, clearance may build up between the outer race and the eyelet, whereby the bearing will move freely in and out... The rubbing with the screw head will cause wear and potentially loosen the screw...





The situation wouldn't be improved if the bearing were pressed from the outside. The bearings should be in the link, not the triangle, as per the SC assembly shown below.





Yellow is a tube for taking up some of the axial force exerted on the bearings by the screw. Here, the bearings are mounted in the link and rely on the rigidity of the link between the two eyelets. The bearings cannot slide out.

Dammit, the 831 link and triangle need to be redesigned!!

A not too drastic redesign would be to provide something for keeping the bearing in the eyelet, such as a retainer ring.

What about the assembly of the lower link to the triangle? I haven't looked close at that yet.

What about the gap to the left of the bearings? The one between them and the aluminum linkage. Is that a concern?

[JJJ]

Maybe this was covered, but did anyone find a US based source for the Derailer hanger and more importantly the nut the axle bolts into?

No US source, this is a Chinese frame! The hanger is available on Aliexpress here https://www.aliexpress.com/item/1005001935571629.html
Choose the "FS831 Use".

[JJJ]

What about the gap to the left of the bearings? The one between them and the aluminum linkage. Is that a concern?

No concern, no parts can move to fill in that gap - the inner and outer races of a ball bearing can't move axially relative to each other.

[sips56]

I don't know if it fits, but Cube brand bikes has some models with a derailleur hanger that looks the same. I don't know if it will definitely work or how hard it is to find, but would at least be something to search for. Also, the threaded part should come with the hanger and be part of a set that sandwiches part of the frame in the middle and has a screw that holds everything in place.

Yeah that is what I found as well.  Ended up ordering for bike inn UK as nobody over here carries Cube pieces.  This bike is starting to be a money pit, and with the pivot issue I am starting to lose hope it will work out and be a scalable solution for my customers. It is a shame because it is pretty dam close to be a great bike.

[slo]

Inevitably, when the triangle is submitted to lateral forces, the bearing will end up sliding to this position, where the eyelet contacts the screw head, and rubs against it as the triangle and link rotate relative to each other. After a while, clearance may build up between the outer race and the eyelet, whereby the bearing will move freely in and out... The rubbing with the screw head will cause wear and potentially loosen the screw...

What about using bearing retainer compound? I had a similar problem on a different frame with the bearing race in the rear upper triangle that was machined too deep which allowed the bearing to move in the race. The bolt head was flat and tightening was limited because it contacted the link and not the bearing. Adding washers and bolt length would not solve the issue. I used Loctite 603 to fix the bearing in the race and it seemed to fix the issue although I did not use the frame much after that.

[JJJ]

What about using bearing retainer compound? I had a similar problem on a different frame with the bearing race in the upper triangle link that was machined too deep which allowed the bearing to move in the race. The bolt head was flat and tightening was limited because it contacted the link and not the bearing so washers would not solve the issue. I used Loctite 603 to fix the bearing in the race and it seemed to fix the issue although I did not use the frame much after that.

That means taking the bearing out and pressing it back in with the compound, right? Not sure the bearing will come out unharmed, meaning a new bearing would have to be pressed in. And then it would be even harder to replace in the future...

I was thinking about drilling two or three holes radially in the eyelet around the bearing, and threading them for grub screws that you could tighten against the outer bearing race. Not sure how well carbon can be threaded, though.

[sips56]

That means taking the bearing out and pressing it back in with the compound, right? Not sure the bearing will come out unharmed, meaning a new bearing would have to be pressed in. And then it would be even harder to replace in the future...

I was thinking about drilling two or three holes radially in the eyelet around the bearing, and threading them for grub screws that you could tighten against the outer bearing race. Not sure how well carbon can be threaded, though.

I removed the bearings yesterday and had no issues. You just need the right bearing tools to do this.

[sips56]

What about using bearing retainer compound? I had a similar problem on a different frame with the bearing race in the rear upper triangle that was machined too deep which allowed the bearing to move in the race. The bolt head was flat and tightening was limited because it contacted the link and not the bearing. Adding washers and bolt length would not solve the issue. I used Loctite 603 to fix the bearing in the race and it seemed to fix the issue although I did not use the frame much after that.

Did you put the loctite on the inner race and bolt or on the outer race and the carbon frame?

[Jotegr]

I removed the bearings yesterday and had no issues. You just need the right bearing tools to do this.

What proper tools are those? Neither of my pullers fit inside the rear triangle.

[sips56]

What proper tools are those? Neither of my pullers fit inside the rear triangle.

I have several sets of press tools  including the rrp http://www.rapidracerproducts.com/products/tools/bpet.html

[FlaMtnBkr]

Since the bolt presses against the inner race coming from the outside, you should be able to tap the bearing out fairly easily since it's not in a blind hole. Mine moves so easy it will probably fall out or take a light press with a finger tip.

[JJJ]

Since the bolt presses against the inner race coming from the outside, you should be able to tap the bearing out fairly easily since it's not in a blind hole. Mine moves so easy it will probably fall out or take a light press with a finger tip.

I believe this is the root cause of the "flex" issues. The press-fit was botched on some frames, and those where the bearings are still tight are OK for the moment, like mine. But this is only temporary, alas. The bearings will end up moving axially and loosen. Then you need to fill the clearance on the screw side with a washer, but then the parts will rub, which makes no sense with a ball bearing mount.

[JJJ]

Back again with some comments on the upper link bearing mount.

On the left, the actual mount, to scale. On the right, the nearest correct way to do it - an elastic retainer ring holding the bearing in its recess.



This is a suggested (IMHO good) correction for the existing frames, to scale, using a standard pair of 6703 bearings that fit in the recesses for the bolt heads. Needs a new pair of bolts as drawn - I have a mechanic workshop in the neighborhood, and will check if they can do this and for how much. Probably cheaper if I can order a certain number of pairs. A minor issue is the tolerance of the carbon width (approx. 3mm) between the two bearings, and whether the inner race of the new bearing will rub against the carbon. I've ordered a pair of 6703s to experiment with.

[sips56]

JJJ let us know if you are moving ahead with bolt creation after your initial testing. I would happily buy in.
 

[slo]

Did you put the loctite on the inner race and bolt or on the outer race and the carbon frame?

Just to be clear this was a fix for a different frame, not the AM831. It was a similar issue although not the exact same configuration. The bearing was loose in its seat and the lateral sliding caused the rear frame to move excessively. I used the retaining compound to hold the bearing in the frame. Similar to the proposed retainer ring or set screw solutions. However it is not ideal because removing the bearing would be difficult.