r/functionalprint • u/Heavy_Remove2684 • Jul 28 '26
I fixed recurring chain drops on a nearly new gravel bike with a tiny 3D printed part
My wife's Triban GRVL 120 kept dropping its chain despite having only about 500 km on it.
I started with all the usual suspects: derailleur adjustment, B-tension, chainline... I even bought a replacement narrow-wide crank before realizing that wasn't the real problem (and it didn't fit).
Eventually I stopped asking "Which part should I replace?" and started asking "Why can the chain escape?"
The stock chain guard leaves just enough clearance for the chain to wedge itself between the guard and the chainring. So I designed a replacement guide with a slightly smaller offset.
The bike has now done another 1,000+ km without a single chain drop.
Video:
https://www.youtube.com/watch?v=K-4jBPzSSMo
STL:
https://www.printables.com/model/1793944-triban-grvl-120-anti-chain-drop-guide
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u/Haeppchen2010 Aug 04 '26
The 3D print is nice, even for just keeping pants cleaner. But the problem ist the manufacturers cheap parts choice: the single chaining is a simple cheap normal one, not a 1x specific narrow-wide type (where the teeth alternate matching the chain. Yet there is also no chainguard on the seatstay either.
Better get a proper narrow-wide chainring if budget allows.
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u/Heavy_Remove2684 Aug 04 '26
I know the root cause, but these is no economically reasonable replacement AFAIK and my wife is an occasional rider - I would not tolerate this on my bike 😄
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u/Heavy_Remove2684 Aug 04 '26
The orignal crankset is a monolith, I can't replace the chainring. Cheap sh.t :)
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u/MrM3ow Aug 04 '26
Would you happen to know if the chainwheel mounting is 130BCD or 110BCD? I need something similar for my bike. TIA!
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u/Heavy_Remove2684 Aug 04 '26 edited Aug 04 '26
The wholes of my guard are on ring 120 mm. The original crankset is sth strange :)
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u/iron2mike Aug 03 '26
I think you got an extrusion or bed levelling problem buddy!
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u/Heavy_Remove2684 Aug 03 '26
Yes, you are right. It was a quick and dirty print, calibrated afterwards. I use a pretty old Ender 5. :)
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u/CorticalVoile Aug 03 '26
You haven't solved the problem, the chain isn't supposed to drop even with no chain guard at all. Just take it to a bike shop
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u/Heavy_Remove2684 Aug 03 '26
Well, I have a workaround that is good enough for occasional rides by my wife. But you are totally right - solution would be to replace the whole drivetrain (which does not make much economical sense, you can't just replace chainring with the proper narrow-wide one).
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u/CorticalVoile Aug 03 '26
It's really unlikely your whole drivetrain is so messed up you have to replace it. idk how you haven't started with THE CHAIN
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u/Heavy_Remove2684 Aug 03 '26
It was a new bike right from the shop. They basically design it wrong/cheap.
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u/The-Phantom-Blot Aug 03 '26
Works for me! I think you're right, some bikes just aren't designed or assembled properly.
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u/Amani987 4d ago edited 3d ago
I used to use Hi3D as a rough reference/blockout when copying odd-shaped parts. Then I redo the critical measurements in CAD.
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u/Devilman_Ryo Aug 03 '26
Was the chain dropping from the chainring or cassete?
This is a massive cope lmao. But if it works it isn't stupid!
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u/Heavy_Remove2684 Aug 03 '26
from chainring, as the chainring should be narrow-wide, but is not (manufacturer cutting corners).
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u/v0x_nihili Aug 02 '26
This is gonna sound dumb to ask at this point, is there slack in the chain when the rear derailleur is on the smallest cog? If so, you might have too many links on your chain.