The Shiny New AM831 Group Buy (A) Thread!

[sips56]

I don't have this frame but these Look like main pivot bearing preload spacer sleeve and the spacers that go between the mainnpoivot bearings inner races and the linkage.

The sleeve sits inside the frame between the pressed in bearings.

One would think and these conclusions are logical, but the sleeve seems to have no home, and these beveled bushings/spacers only seem to fit and/or make any sense on the upper most link on the top tube. That said, there is another set of spacers that did not have a bevel that fit behind those bearings in what seemed like a better way.

Anyone who has the frame and disassembled please provide any guidance you may have from disassembly as what bushings/spacers go in each pivot location.

Thanks,
Luke

[FlaMtnBkr]

The video above says TanTan down in the corner which means another (3rd or 4th?) company making them. I would be curious how that works because it's not the only frame made by more than one company which all seem to be manufacturers that claim to make frames. I'm wondering if it's something like a shared workshop or makerspace where tools and molds are co-owned or rented to reduce investment costs? And why you will see areas with multiple businesses of the same type in a small area if you search and map one of their addresses.

I don't really like saying this, but I think this frame has a pretty serious design flaw with the upper linkage and connection to the rear triangle/ seat stays. It can probably be made to be rideable in most cases, but what is left to be seen is how it effects the frame in the long term. I'm guessing there will be flex or bearing problems on most frames eventually. If it were me I think I would stop making frames and address it now instead of making more with problems. And I think it would be an easy fix. Would be nice to get some input from the maker and not just invitations to a group buy...maybe we also need a pole to see how many people with the frame are having issues already?

I think I will start a new thread with my build and what I've run into and try to get some pictures to help show what I'm talking about. I need to pull some stuff apart and take some pictures so might be a few days. I noticed something was wrong and made a washer to help a long time ago, but didn't really look at the design until I was messing with it a few days ago and there is definitely a problem.

Anyways...I really want to like the bike but at this point I don't think I would buy it again, at least not until a couple issues get worked out. And I think the only way that will happen is if current owners get vocal and let the maker(s) know there is a problem, as well as potential  buyers that most likely don't want something that doesn't work right...

[scourge]

You can count me as on having problems with flexing in the frame. I even posted a vid in the other thread. Really hope there is a fix to this. A simple fix would be great, but even if it's buying a new linkage or rear triangle I just hope a good fix comes.

[cybrsrce]

The video above says TanTan down in the corner which means another (3rd or 4th?) company making them. I would be curious how that works because it's not the only frame made by more than one company which all seem to be manufacturers that claim to make frames. I'm wondering if it's something like a shared workshop or makerspace where tools and molds are co-owned or rented to reduce investment costs? And why you will see areas with multiple businesses of the same type in a small area if you search and map one of their addresses.

I don't really like saying this, but I think this frame has a pretty serious design flaw with the upper linkage and connection to the rear triangle/ seat stays. It can probably be made to be rideable in most cases, but what is left to be seen is how it effects the frame in the long term. I'm guessing there will be flex or bearing problems on most frames eventually. If it were me I think I would stop making frames and address it now instead of making more with problems. And I think it would be an easy fix. Would be nice to get some input from the maker and not just invitations to a group buy...maybe we also need a pole to see how many people with the frame are having issues already?

I think I will start a new thread with my build and what I've run into and try to get some pictures to help show what I'm talking about. I need to pull some stuff apart and take some pictures so might be a few days. I noticed something was wrong and made a washer to help a long time ago, but didn't really look at the design until I was messing with it a few days ago and there is definitely a problem.

Anyways...I really want to like the bike but at this point I don't think I would buy it again, at least not until a couple issues get worked out. And I think the only way that will happen is if current owners get vocal and let the maker(s) know there is a problem, as well as potential  buyers that most likely don't want something that doesn't work right...

Agreed, A manufacturing fix would be an upper link that has bearings like the HT2 - https://www.santacruzbicycles.com/en-US/bike/hightower/2-carbon, some modification to how the triangle attaches, and a different stronger layup of the seat stays to prevent roll even when you have good positive contact at the linkage.

If you don't mind the feeling like you have a flat and a really unpredictable rear wheel path at the most inconvenient times, this may be the frame for you. 

[Snacks]

Do you guys think if we were to replace the upper link with a HT2 link it would fix the problem? Granted, that's assuming it would fit

[Deso]

Fitting a SC link in there would be great. anyone able to test this? If so.. they are only 60 euros to order online.. doubt it though

[JJJ]

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.

[JJJ]

Interesting. The lateral testing around 20sec doesn't seem to have any slop or play in the rear triangle that some users are having.

That's not "lateral" testing the rear triangle - they're applying torque to the bottom bracket to test the torsion of the front triangle.

[sips56]

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.

JJJ thanks for sharing. This definitely helps everyone who has not studied this linkage for hours understand the issue happening inside this pivot. I am not convinced however that it is only the linkage at fault. I believe this is part of the issue (and likely easier to correct) than the 2nd issue which I believe is the triangle being flexy on its own. If anyone has evidence to support that the triangle is appropriately stiff because they jammed enough nylon into the pivot that it stopped flexing all together (within what we know is acceptable based on other bikes) please prove me wrong. I have inserted the outer bushings by making a custom set of nylon spacers. It seems to be helping some. I also inserted some smaller “janky” inserts race but It was binding the whole pivot from moving freely which was unacceptable. Perhaps if some perfectly toleranced metal inserts where made it would work, but to JJJ points the engineering is faulty.

Why didn’t they just replicate the SC pivot?  I rode with a friend yesterday that had a hightower and studied it pretty closely. The bike is very similar with the major difference being how they handled this set of bearings and pivot. Why they decided to reinvent the wheel on this is beyond me. Seems like they should have stuck with both sets of bearings in the pivot. They did so for the top bearings in the link, but decided to do their own thing for the lowers. Can only assume it was related to production efficiency or something similar.

[sips56]

Do you guys think if we were to replace the upper link with a HT2 link it would fix the problem? Granted, that's assuming it would fit

It is more complicated than that. You would need the triangle to be re-designed to accommodate a bolt through rather a bearing i.e with the bearing removed from the triangle something needs to fill the space. 

[Snacks]

It is more complicated than that. You would need the triangle to be re-designed to accommodate a bolt through rather a bearing i.e with the bearing removed from the triangle something needs to fill the space.

Why do you need to remove the bearing? Would it be terrible if you left it there and it sat against another bearing? Well, as long as the bolt fit through it.

Fitting a SC link in there would be great. anyone able to test this? If so.. they are only 60 euros to order online.. doubt it though

I totally would have but they are sold out here in the states

[FlaMtnBkr]

JJJ, thanks for doing that! I have a post that I've been trying to describe it all and started on drawings last night, and you have done it all so I don't have to! And it looks a lot better than what I have so far.

I think the pictures probably really help others see what is going on.

On my frame, if I pulled on the seat stay there was very obvious movement so I made a washer to fill the gap under the bolt head and the carbon of the frame. This reduced the play but I didn't stop to look at the design and what was actually happening. Since the bolt is holding the bearing tight to the linkage, when the frame moved over the bearing was sliding in and out of the frame. The washer just limits the movement but between the bearing moving in the frame and the bolt rubbing on the frame or washer if installed, things are going to start falling apart pretty quickly.

I also haven't looked at the lower link as it isn't as easy to get to. But the bearings are in the linkage so hopefully it will be better. I might as well pull it apart because I still can't get the shifting very good, I'm assuming because the derailleur hanger is out of Sram specs, and have only ridden the bike around the yard. I'm surprised others aren't having issues with poor shifting. While I am picky about shifting, it's not even good enough to go out of the yard and a second issue that needs addressing IMO. After seeing what's going on at the linkage I don't expect to be riding this any time soon or ever if there isn't some kind of fix.

[sips56]

JJJ, thanks for doing that! I have a post that I've been trying to describe it all and started on drawings last night, and you have done it all so I don't have to! And it looks a lot better than what I have so far.

I think the pictures probably really help others see what is going on.

On my frame, if I pulled on the seat stay there was very obvious movement so I made a washer to fill the gap under the bolt head and the carbon of the frame. This reduced the play but I didn't stop to look at the design and what was actually happening. Since the bolt is holding the bearing tight to the linkage, when the frame moved over the bearing was sliding in and out of the frame. The washer just limits the movement but between the bearing moving in the frame and the bolt rubbing on the frame or washer if installed, things are going to start falling apart pretty quickly.

I also haven't looked at the lower link as it isn't as easy to get to. But the bearings are in the linkage so hopefully it will be better. I might as well pull it apart because I still can't get the shifting very good, I'm assuming because the derailleur hanger is out of Sram specs, and have only ridden the bike around the yard. I'm surprised others aren't having issues with poor shifting. While I am picky about shifting, it's not even good enough to go out of the yard and a second issue that needs addressing IMO. After seeing what's going on at the linkage I don't expect to be riding this any time soon or ever if there isn't some kind of fix.

Mine is shifting perfectly with Shimano 12 speed and a 51 cassette. This may just be your setup which I would say is a good thing as you just need to work it out.  The frame play...well that is definitely a bigger issue.

[Maffly]

I think the carbon is stiff enough in the rear triangle. I have nylon spacers in there now that have it working well but I doubt it will hold up long. I put some perfectly sized aluminum spacers off of an Evil pivot in there and it was as stiff as any bike I own. Suspension did not move freely though and would also cause damage.  I think we have all diagnosed the problem correctly. Bearings in the link or pressed from the outside would both have worked. Plenty of bikes do it both ways. The question now is what to do about this.  I think Eddy needs to step up and offer a legitimate fix(doubtful) or refund/return options.  If not we need to warn others about this frame. 

[JJJ]

On my frame, if I pulled on the seat stay there was very obvious movement so I made a washer to fill the gap under the bolt head and the carbon of the frame. This reduced the play but I didn't stop to look at the design and what was actually happening. Since the bolt is holding the bearing tight to the linkage, when the frame moved over the bearing was sliding in and out of the frame. The washer just limits the movement but between the bearing moving in the frame and the bolt rubbing on the frame or washer if installed, things are going to start falling apart pretty quickly.

Yes, I guess you're unlucky there. My bearings don't move in and out of the eyelet... yet. But I do have some traces of rubbing from the screw head.

I've attached a potential fix, using a second ball bearing on the outside. It does need crafting a custom screw, though.