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Discussion Starter · #1 · (Edited)
When doing suspension service on my BMC Fourstroke 01 frame I spoted that lower link rotating too hard. When I removed all hardware from frame I saw those cracks or whatever this is.
I'm interesting: is this is "normal" wear in place where aluminium pivot is glued to the carbonframe, or this is signs, that my frame is broken?
Do I need to remove paint from those area to be sure? If yes, can someone suggest secure and simpliest way to do this?
 

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Mine also had that going on, but take a look at the top pic. Mine had some major cracking going on around the bottom bracket area. It started with small hairline stress and then it progressively got worse.

Just this past month I wound up having my frame replaced under warranty. My shop handled it all for me with just doing photos, which was great because I was able to keep riding until I had everything ready for my swap.
 

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Discussion Starter · #5 ·
BMC customer services didn't response for a while. I'm planning to go to the local carbon shop for repair.
But before I will go there I want to strip paint from the frame. Can someone suggest better way to do this, or stick with good old sandpaper?
 

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Interesting I also had a similar experience with my frame. Here is a pic of my BMC FS01. I had it replaced last year after my shop discovered this when servicing my suspension. They worked with BMC for replacement and it took about 2-3 weeks to get the new frame. Would you consider not stripping paint and try to negotiate with BMC for replacement? I think once you start removing paint you are reducing any chance of getting a warranty replacement. Best of luck on whatever route you take! I know it's disappointing and frustrating being off the bike.
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Discussion Starter · #9 ·
Here I found similar story about russian local racer and his fourstroke frame. Only downside this article wrote in russian language.
https://twentysix.ru/blog/multig/126586.html

In short:
Greate frame, but during one of maintenance the same cracks was found. BB was repaired in local shop. And he can rode for another year or so, before crack started to develop again.

P.S. He has another problem with one of bolts. Because author being unable to buy new hardware new custom-made bolt was created, but due to the measurement error it's diameter was 0.5mm less than original and aluminium pivot after couple of years broke as well.

P.P.S. If you have the same frame and you warranity is expired (it is very possible, because literally the same frame was produced from 2013 to 2017 and maximum you could get - 3 years when you register it) and you see those crack on your frame:
1. You can sold it ASAP;
2. You need to take it to the local shop, where lower link can be fixed with additional layers of carbon fiber. The sooner you can do it, the better.
 

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I have three broken Fourstroke frames in my garage. Sold the fourth one and went with alloy Smuggler. I must take hat off for my local shop who did all the negotiations with BMC. I started with FS2 frame and at some point got upgraded to FS1, because they did not have FS2 frames anymore.

IMO the construction is flawed. Quite a small alloy tube glued into the carbon frame. When you hit something it will easily break loose. And you cannot fix it anymore. Carbon and aluminium are electrochemically agressive and carbon will eat aluminium when air and moist will get between them. You cannot glue the tube anymore. I tried it (by professional carbon repair shop and they warned me up front about this) and failed. All area around the lower tube went soft eventually. Also the way how aluminium plugs are pressed into the tubes to retain the ball bearings and are really hard to remove without hammering them out is just poor engineering.
 

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Discussion Starter · #13 ·
Finished product.

When I started, I didn't want to paint repaired places, just want to polish them and put some varnish. But after all carbon work is done, I realise that due to the all those curves in BB area I can't polish them well and create beautiful transfer region between repaired place and original paint.

You can clearly see now all places, where additional layers of carbon was added, those regions visually much thicker.
 

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I have three broken Fourstroke frames in my garage. Sold the fourth one and went with alloy Smuggler. I must take hat off for my local shop who did all the negotiations with BMC. I started with FS2 frame and at some point got upgraded to FS1, because they did not have FS2 frames anymore.

IMO the construction is flawed. Quite a small alloy tube glued into the carbon frame. When you hit something it will easily break loose. And you cannot fix it anymore. Carbon and aluminium are electrochemically agressive and carbon will eat aluminium when air and moist will get between them. You cannot glue the tube anymore. I tried it (by professional carbon repair shop and they warned me up front about this) and failed. All area around the lower tube went soft eventually. Also the way how aluminium plugs are pressed into the tubes to retain the ball bearings and are really hard to remove without hammering them out is just poor engineering.
I'm looking to buy carbon rear triangle for my BMC FS in size M. Is this something you might have for sale out of your three broken frames?
 

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Had the same problem on FS02 after a few months of riding. The dealer now replaced the frame under warranty by the new model FS01 fullcarbon with RAD. Hope BMC solved it. The drivetrain and rear wheel don't fit (boost an no front derailleur option) but otherwise the frame is top spec. I'll put Shimano 1x12 on it.

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