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Discussion Starter · #1 ·
I have a 2017 BMC Roadmachine 01 with the custom D-shaped carbon seatpost. Recently the longer of the two bolts that go vertically thru the top of the seatpost into the clamps that hold the rails of the saddle snapped in half. I was able to easily remove the bolt and replace temporarily with a hardware store M5 version (and little o-ring) that is close but not quite the same. Local bike shop contacted BMC and they will only sell me the complete seat post (with clamp and bolts). I scoured the internet for this bolt and cannot find it. I think it would be called something like "M5 Socket Cap Head 45 mm length - half thread. But the part is non-standard because of the taper from the cylindrical head to the bolt shaft that allows it to fit snugly into the carbon cavity recess of the seatpost. I have attached a picture. So has anyone else experienced this and more importantly have any idea how to find a replacement bolt? Thanks!

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You could try mcmaster.com but if you don't find a satisfactory replacement then your best bet is just buy the entire post. It saves a lot of fruitless searching.

Friends never let friends buy bikes with proprietary parts.
I may be way wrong... but I shopped frames online for a year. BMC seat-post clamp was a recurring problem .


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Discussion Starter · #5 ·
Use the bolt you got, get some finish washers, pick one and drill it out to fit the bolt, done.

Good idea, thanks! Hope I can find one small enough.
 

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BMC really needs to step up their customer service and offer these bolts for individual sale.

To ask a customer to spend big $ to buy unnecessary parts in order to get the correct bolt is ridiculous. Or at least supply warranty dealers these bolts so they can replace them once worn, etc.

I believe the reason for the beveled bolts is to allow the bolt head to lay flush or below the surface. I could be wrong but I’m not sure if is for strength or structural integrity.

Maybe try to reshape a rubber grommet so it sinks into the recessed part of the seat post. Put the bolt into the grommet.

Please let me know how it goes or what you ended up doing.
 

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BMC really needs to step up their customer service and offer these bolts for individual sale.

To ask a customer to spend big $ to buy unnecessary parts in order to get the correct bolt is ridiculous. Or at least supply warranty dealers these bolts so they can replace them once worn, etc.

I believe the reason for the beveled bolts is to allow the bolt head to lay flush or below the surface. I could be wrong but I’m not sure if is for strength or structural integrity.

Maybe try to reshape a rubber grommet so it sinks into the recessed part of the seat post. Put the bolt into the grommet.

Please let me know how it goes or what you ended up doing.
Agree. Especially when a company uses proprietary solutions for things, they need to step up and really support those products. BMC frames don’t come cheap. A boutique brand should provide boutique customer service.


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I have a 2017 BMC Roadmachine 01 with the custom D-shaped carbon seatpost. Recently the longer of the two bolts that go vertically thru the top of the seatpost into the clamps that hold the rails of the saddle snapped in half. I was able to easily remove the bolt and replace temporarily with a hardware store M5 version (and little o-ring) that is close but not quite the same. Local bike shop contacted BMC and they will only sell me the complete seat post (with clamp and bolts). I scoured the internet for this bolt and cannot find it. I think it would be called something like "M5 Socket Cap Head 45 mm length - half thread. But the part is non-standard because of the taper from the cylindrical head to the bolt shaft that allows it to fit snugly into the carbon cavity recess of the seatpost. I have attached a picture. So has anyone else experienced this and more importantly have any idea how to find a replacement bolt? Thanks!

View attachment 480034

View attachment 480035
I have a 2017 BMC Roadmachine 01 with the custom D-shaped carbon seatpost. Recently the longer of the two bolts that go vertically thru the top of the seatpost into the clamps that hold the rails of the saddle snapped in half. I was able to easily remove the bolt and replace temporarily with a hardware store M5 version (and little o-ring) that is close but not quite the same. Local bike shop contacted BMC and they will only sell me the complete seat post (with clamp and bolts). I scoured the internet for this bolt and cannot find it. I think it would be called something like "M5 Socket Cap Head 45 mm length - half thread. But the part is non-standard because of the taper from the cylindrical head to the bolt shaft that allows it to fit snugly into the carbon cavity recess of the seatpost. I have attached a picture. So has anyone else experienced this and more importantly have any idea how to find a replacement bolt? Thanks!

View attachment 480034

View attachment 480035
This is a safety issue that deserves a recall.

I've had a bolt break on my 2018 RM02 break 4 times. BMC and my LBS have been kept in the loop each time. So far they have been 1. responsive and empathetic, but 2. not actually that helpful.

Bolts cannot be purchased and they are proprietary to BMC. Very aggravating. BMC has sent me replacement bolts (twice) at no charge. The first time they warranted the entire seatpost/assembly and the second time they sent the just clamp and bolts. In both cases there was no cost to me. However, the larger issue with bolts breaking has not been addressed and is much more concerning.

I would strongly advise against using anything other than BMC parts. If you use other parts you risk BMC or your LBS holding you accountable. You should reach out to BMC and your LBS, documenting every step along the way. The bolts should be 6mm, not 5. Also, a mechanic pointed out that their seat clamp does not nest well on the seatpost when torqued to specs. That adds shear forces on the bolt, making the (undersized) bolt even more likely to break.

Again, This is a safety issue that deserves a recall.
 

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Can you chuck a proper sized hardware store bolt into a drill and hold a file to the bolt head while the bolt is being spun by the drill to create the taper that is needed? Kinda like a cheap version of a lathe.
It would be easiest in a drill press, but a hand drill would perform the same function if steadied on the edge of a bench.
 
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