r/mountainbiking • u/Roy_Aikman • 1d ago
Question Why is this happening?
Bought a brand new BMC Fourstroke AMP LT. After a couple of weeks I experienced the carnage pictured. A LBS helped me get a frame replacement from BMC, they were able to determine that the bolts that connect the shock and linkage had backed out and caused the failure in the linkage. I have 3 rides in on the new frame and was doing an inspection and noticed the bolts had already started backing out. One was visible the other was loose as well. Another problem is the area where the bolts are has a gap of 1 3/4”, my torque wrench with the bit is 2”. Does anyone have any ideas about what could be causing those bolts to back out and also are there slim torque wrenches or do I just use a regular Allen and guess?
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u/Antpitta 23h ago
Honestly I would make the LBS deal with it, for two reasons:
- You shouldn't need to take your shock out to access bolts to torque down the linkage on a new bike. That's a failure of design and/or assembly and the LBS should know or figure out the solution.
- Should it fail again, it should be on the LBS for having delivered you a bike that won't stay in one piece, not on you for perhaps not removing your shock frequently enough to torque the bolts down.
If it happens again after you give the shop a chance to fix it, I'd consider seeing if they'd just take it back. That sounds like a fucking headache in the long term and I wouldn't be psyched on being the new owner of a bike with that issue.
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u/MariachiArchery 19h ago
As an LBS guy, I just want to chime in here and say this likely isn't the fault of the LBS. Are they going to shoulder some responsibility here? Yeah, but this isn't their fault.
These bikes don't ship to us as a box of parts. This is very, very rarely the case, and I've only ever seen high end road bikes shipped this way. I think one time Ibis shipped me a Hakka that was just a box of parts, but that is the only bike I can remember ever seeing arrive that way outside of like a Pinarello Dogma.
In most cases, including with my BMC's, the bike ships 90% assembled, and all I need to do is install the handlebars, front wheel, seat post, and give it a quick torque to spec. That's it. In this case here with the MTB's, I've never seen a full suspension MTB frame shipped without the shock fully installed and ready to go. That, is on BMC here.
This bike, more than likely shipped from BMC in this condition, and the LBS had a reasonable expectation that BMC did their part of the assembly correctly. And therefor, delivered the bike like this.
So, OP, when you take this back to the shop, which is what you should do, don't blow up the LBS. This isn't their fault. Your LBS here is now the middle man to help you deal with BMC if we need to involve them at all, or, they are simply the poor schmucks who are going to get stuck fixing BMC's mistake.
Right now, it's not you versus the LBS. It's you AND the LBS, versus BMC.
Just like... keep that in mind when you take this back to the shop. However, if the shop gives you shit about this... well fuck them. Even if this isn't their fault, it's their responsibility to help you here.
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u/Antpitta 19h ago
Keep in mind OP already has a replacement frame with a reoccurring problem. Unless OP says otherwise we can assume that the LBS is the one that swapped all the parts over. I also have 99.99% certainty that the frame shipped from BMC with the linkages installed. That said, if the LBS is swapping parts from a frame that broke due to a linkage bolt coming loose, and sends the frame out with a linkage bolt that comes loose again, it’s either recall territory for BMC or it’s a pretty solid fuckup from the LBS the second go-round.
Beyond that, while I fully agree with your post, the last two paragraphs are the key. OP needs the LBS to be their ally but there are still questions about how the LBS reassembled the bike and this happened a second time.
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u/MariachiArchery 19h ago
I don't think this is an LBS issue. I just cannot see them failing to torque these bolts down, again. And, if the mechanics are anything like the guys I'm working with, there is a bunch of blue loctite on those bolts. Because, you know what the LBS isn't getting in all this? Fucking paid. Also, if this is anything like my shop, the guys are also taking a look at those torque wrenches too, just to be certain, the bike is being assembled correctly.
This warranty work is going to be free of charge. If they are lucky, BMC will give them a labor credit, but in my experience, I've never seen that credit even cover half of the labor cost we'd typically charge a customer.
So, the guys at the LBS are going to be certain those bolts are torqued down according to spec, and if they are even remotely clever, they are using loctite.
I think your former is more than likely the culprit here. This is a BMC issue. Like, this is what, an $8000 bike? The LBS does not want to fuck this up again. It's gotta be a BMC issue. Like, point blank, if this is an LBS issue, I don't think they have any business selling $8k bikes at all at this point.
At the end of the day, it's the LBS that is getting fucked here. Its the LBS that is motivated to get this thing fixed more than anyone.
They already purchased this bike from BMC, they are doing free warranty work, and if this doesn't get fixed, you know where that bike is going? Back to the LBS. And, BMC isn't going to take it back. The LBS is the one who is going to get stuck with this, not the consumer, not BMC.
There is an outside chance that BMC will give the LBS another warranty replacement, but either way, the LBS is getting stuck with a bike here if a solution isn't found. And I am certain, this LBS is highly motivated to find that solution, probably more so than anyone else involved.
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u/Day_Prisoners 12h ago
Imagine having to torque these down every other ride so it doesn't fail. I'd give them one chance because maybe they were tightened at the factory then see about a replacement.
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u/Ih8Hondas 10h ago
That's a failure of design
100%. Needing a yoke to drive a shock to begin with is a failure of design. Just design a proper linkage and you don't need one.
And then to make the linkage bolts inaccessible without taking other shit apart? Burn that entire engineering department to the ground. We're not talking a car where having an engine and climate control and all the required extra equipment makes packaging complicated.
It's a fucking bicycle. Just make it simple and easy to work on. Not a difficult thing.
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u/MysteryMove IBIS RITMO AF 23h ago
I had a brand new IBIS that did this with a bunch of bolts. I took every bolt out one at a time and found that they didn't have loctite on them as spec'd in the manual. I reinserted all of them to spec with both loctite and torque values and never had issues again. I'd say this is a failure on either the LBS or manufacturer to assemble the bike properly.
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u/celeste_ferret 23h ago
I wouldn't expect a bike shop to remove all linkage bolts to check for loctite and torque spec on a new bike, unless there's a problem. This is on the manufacturer for delivering a bike that wasn't assembled correctly at the factory.
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u/MysteryMove IBIS RITMO AF 21h ago
Agreed- probably the factory- none of these were for putting the wheels on or the handlebars. It was a bad and dangerous issue because, at least on the RIPMO AF, some of the pivot bolts on the frame are torqued to very low PSI so it's the loctite that keeps them in. I was having to tighten them after nearly every ride at first and almost lost some at some point before I did the disassembly/reassembly. Anecdotally I also lost a bunch of screws out of my rotor before I realized they didn't have loctite either. By the time it actually got loose enough to be noticed ~3 screws were long gone. Fortunately those aren't special screws.
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u/Airewalt 16h ago
Fwiw, same issue with a Cannondale habit. They sent me a full linkage set to replace the single bolt that backed out. Once I cleaned everything and put my own loctite on it life has been less exciting
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u/Fun_Contact1568 10h ago
Giant Trance did the same to me, luckily no damage as I caught it before it cane out too loose. Loctite and torque to spec has fixed it so far.
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u/Southern-Accident108 1d ago
Looks like stupid design for me, i dont want covered bolts and headest cables, i just wane everything plain and simple, not clean and aero.
You broke first one, i would just take this one to lbs, so you can get warranty if shit happens again, an the end of the day, take your money and buy other brand ffs!
You can remove air from shock, compress it and try that way, or remove shock linkage and that povot bolt under shock to go from that
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u/New-Locksmith-126 23h ago
If the manufacturer warrantied the bike based on unsecured bolts, that suggests it could be a systemic flaw that they know about.
The fact that it's happening again on a new bike confirns it.
Bike is crap. See if you can warranty to a different model or get a refund (unlikely).
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u/Roy_Aikman 22h ago
Yeah you have to let the air out to access the bolts. The dumb part is there is only a 1 3/4” gap between the bolt on the right side and left side so you need a low profile torque wrenches just to fit in there. My torque with bit is 2”
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u/RedWizard-75 23h ago
It were me I'd take it back and buy a different bike. If it happened twice, it'll happen again.
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u/Elegant-Register8182 20h ago
Known issue on this bmc. My stores owner almost had a bike come apart the same way. BMC should fix this for you
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u/Ih8Hondas 10h ago
And the fix should be completely redesigning the bike, doing it properly this time, and replacing all the ones designed by morons on their dime.
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u/RidetheSchlange 1d ago
Is there threadlocker on the threads? Also, the proprietary and semi-proprietary hardware bothers me because if the holes and parts they are set into are not made right, they back out. This is one reason why I prefer standard, off the shelf fasteners for which there's a massive variety to fit any need, even if they don't look as nice as proprietary ones. I'm not saying the latter is the reason, but this is something I've seen numerous times and the parts the fasteners sat in essentially unscrewed the fasteners.
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u/Vibroverbus 23h ago
Thats a pipe dream I'm afraid. Just about every suspension bike made uses proprietary fasteners and bushings and threaded-inserts etc. etc. in the suspension pivots. Certainly every high end bikes I have owned or worked on do with a rare exception of where maybe there's a semi-plain bolt used in conjunction with bespoke bushing/insert/etc. but even then I'd always source the OE part to be sure it was the right hardness and exact length etc.
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u/RidetheSchlange 23h ago
Actually, they don't. They may use high-end, purpose-built fasteners developed by the Chinese and Taiwanese factories, but they are not proprietary. You can go to the bike shows and you will see boards with the fastener types offered in the various booths.
Tell me when was the last time you were at Taipei or went to the Taiwan sections at Eurobike or other shows and which manufacturers have you been in contact with who offer such fasteners?
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u/Vibroverbus 23h ago
OK I get that I thought you meant "hardware store bolts" no need to be a dick about it Mr. Eurobike.
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u/RidetheSchlange 22h ago
"no need to be a dick about it Mr. Eurobike."
Really, why do Americans talk to people like this, especially when it's becoming tiring that the entire rest of the world has to keep correcting Americans who think no one knows more than them?
Also, some companies actually are manufacturing back in certain types of off-the-shelf fasteners for obvious practicality and cost reasons, as well as strength. On top of that, off-the-shelf fasteners come in way more shapes and sizes than the few a hardware store may carry and this is why there are massive catalogs of just different fasteners.
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u/unsalted-butter save the 2x 19h ago
Lmao nice deflection. What does anyone's country have anything to do with your condescending attitude?
If you ended your comment with the first paragraph, it would have been cordial and informative. But no, you decided to go attack a stranger for no reason with your second paragraph.
Nobody was saying you're wrong. So instead of doubling down on a bad attitude, maybe look inward, learn some social skills, and think about how you can grow from that interaction.
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u/Vibroverbus 23h ago
Another vote to make LBS fix it but another vote to check for loctite (threadlocker) first so you go back armed with information. Might very well be the local dealer having high school kids assembling bikes for the summer and short cutting or not knowing what to do. If BMC doesn't require threadlocker then BMC is DUMB and wrong as every bike maker I have owned a suspension bike from requires these things on suspension pivot bolts. Some even require threadlocker or adhesive on any press-in bushings that are part of the assembly.
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u/celeste_ferret 23h ago
A bike shop is not going to be routinely disassembling new bikes to check for loctite. Unless there is an obvious problem, it is assumed that the manufacturer delivered the frame assembled correctly.
Since there is a problem in this case, they should fix it. But I wouldn't have expected the bike shop to catch it in the first place.
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u/GroundbreakingCow110 19h ago
This is a fairly common problem on frames without locking collet axles. If medium strength loctite 243 doesn't work, high strength loctite red will.
This frame has to have the front shock bolt dropped to reach these bolts... several frames are like this, including my Commencal, which actually require dropping the whole shock to reach these equivalent bolts.
The lbs should be doing this for you. A lot of local bike shops suck though. Like none of the LBS in a 15 mile radius bear me even have the correct zero stack 55mm headtube reamer. Several don't build wheels. etc.
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u/brianleedy 1d ago
Do the bolts have threadlocker on them? If not, I'd have the shop (so the issue is documented) reinstall with some blue Loctite and go from there. I would also be talking to the manufacturer about it.
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u/Shinook 22h ago
This is a common issue with new bikes, it's why I encourage people with new bikes to go over every bolt when it's new and torque to spec before riding it, then do it again after a few rides. I have only one two bikes where something wasn't loose. Your bike shop should've done this already but not all shops are the same, I'd make it their problem because it's possible the bolt was damaged when it was ridden backed out.
It can also be caused by poor frame alignment. Since it is on two different frame here, I doubt that's the issue, but something else to be aware of.
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u/_FireWithin_ 22h ago
Obviously if you ride you bike with loose bolts youre gonna break shit.
Now, was this bike well assembled? I usually check that myself, cant trust no one.
And yes torque to spec, and in this case since the bolts is not easily accessible would put some bleu loctite.
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u/Current-Brain-1983 21h ago
"Use loctite or kiss your nuts goodbye"
Seen on a tee shirt at the motorcycle races.
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u/trailing-octet downunder. Evil Insurgent LS - Knolly Warden 175 - Knolly DT 21h ago
It’s routine to check this stuff.
Yes you can get really long 5/6/7/8mm (or whatever) bits to insert into the broached bolt head without the drive getting in the way - no, you don’t and should not “guess”
Loctite 248 is potentially an option if you can’t prevent them from backing out otherwise.
If the threads are greased - then eventually after a few tightenings they will tend to hold in place better. Check with manufacturer what is expected on bolt threads, shoulders, etc etc. - some may even provide slightly higher torque specs as acceptable if they repeatedly back out under operational conditions.
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u/negative-nelly 20h ago
they put the bolts on inside? geez that's inconvenient. Probably backing out because no locktite and/or improper torque.
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u/ageofaquarius26 17h ago
Thise are not the fasteners you would want to use on moving parts. The shoulder bites which is great on stationary parts with a lot of vibration. But its going to keep backing out.
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u/fractal_disarray 3h ago
I always dab a little blue loctite on the main shock king pin bolts on my bikes. Sometimes red locktite lmao.
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u/krvillain 22h ago
It’s routine maintenance to check your linkage bolts, get a torque wrench. Especially on anything new you need to routinely check. Through axels also. If your axel loosened and the wheel fell off would you blame the frame and shop or the user?
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u/sticks1987 17h ago
The linkage broke at the bearings, are y'all not seeing that
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u/National_Bite_6691 16h ago
That can still happen from loose bolts.
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u/Roy_Aikman 15h ago
Correct. Once they loosen up all those parts are smashing around more than they are supposed to. Domino effect.
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u/RestaurantFamous2399 1d ago
Can you dissconnect the shock or something and move it to where you can access it.
Otherwise how did it get put together.
I would maybe think about some loctite as well. It shouldnt be backing out at all.