Single speed conversion issue

[Michael954]

First post, be gentle. I'm in the process of converting a 2019(ish) Trek FX 2 Disc to a single speed. I'm using the DMR revolver kit in the back and up front I bought a Shimano Nexus FC-C6000 crankset. I bought it on eBay but I feel like it may be a European model because I never see it on US sites. I removed the derailers, changed the shifter/brake combos to just brakes (Shimano Sora) and removed links from the chain. The bike looks and rides great, good ratio for me. Sounds like everything is great but here's the issue, the left crank (non-drive) keeps loosening when I ride . After just 3-4 miles I have to stop and tighten it again to the point where I worry about it falling off. I used the hardware that it came with it but something is definitely wrong here. This is the first crankset I've ever changed so I'm far from an expert but I know this shouldn't be happening. Was there maybe supposed to be a lock washer that isn't there? Could I go to a hardware store and buy a lock washer and add it? Did I possibly just buy a piece of crap? Any advice would be great.

[Painkiller]

(08-04-2024, 11:38 AM)Michael954 Wrote:  Shimano Nexus FC-C6000 crankset.

[Jesper]

(08-04-2024, 05:43 PM)Painkiller Wrote:  

(08-04-2024, 11:38 AM)Michael954 Wrote:  Shimano Nexus FC-C6000 crankset.

Is it square taper? You need to inspect the crankarm for damage to the tapers. If all is well try to add some removeable locktight to the threads. Did you buy it used or new?

Those are square taper cranks. I would assume that a JIS taper BB spindle is required. I have never put a JIS arm on an ISO spindle, but it may be that it is "bottoming out" on the spindle. Though, if that was the case I assume both sides would be a problem and not just the left. @Michael954 was the BB assy part of the crankset or did you only buy the arms? What Painkiller says makes sense if those arms are not new (possibly why they were being sold?). You may be owed a refund if they were damaged beforehand, but it may be difficult having already mounted the arm.

[ReapThaWhirlwind]

I've had this happen to me also on square taper cranks. I suspected that something in-between had compromised the square or the spindle to cause this issue. From here, I switched over to octalink and didn't experience it anymore. I further switched over to Hollowtech II, and that would be my suggestion for you moving forward.

Alfine S501 is the primary single speed option for Shimano, but you might (should be able to) utilize a Zee M640 the same.

[Jesper]

The author has yet to inform us as to whether the cranks were new or used. I have never had a steel or Ti spindle damahed by an aluminium crankarm. If they were new and not mounted properly it does not take much time to cause damage to the crank.