I’ve encountered a recurring issue with my left, non gear side, crank arm coming loose. I retighten it as much as possible, even using lock tight, but it it’s loose again within minutes of ride time. Is there some trick I don’t know? Is this just an issue with cheap parts on a Walmart bike?
I've had that happen on a bike years ago that had the old style square taper crank arm interface, but lock tite fixed the issue. The more modern cranks now use other shapes that are less prone to that problem
If the lock tire didnt help it may just be that the crank arm is worn enough it allows it to move incrementally and loosen up. It may just be time to replace the crank or bottom bracket.
Same thing happened to my bike over the past couple of years. Lock tite did nothing to fix it. Turns out the bike shop found that the square hole in the aluminum crank arm had opened up from being loose all the time. Final got a new crank arm and all is well.
If it's a square taper connection, the above is likely the issue - and why that interface isn't really used anymore. A bodge-fix is to wrap the taper with something like an aluminum can, but no guarantees.
TIG weld? <evil grin>
1988RedT2 said:TIG weld? <evil grin>
JB Weld?
I had the same issue on my mtb earlier this year. The original arm came loose on me in the middle of the woods and I wallowed out the hole and messed it up pretty badly attempting to ride it out. Bought a new one and it kept coming loose on me within a few minutes of peddling around the driveway, even cranking the bolt as tight as I dared to get it. I ended up busting out my ball joint press to seat the taper as tightly as I could possibly get it. That fix has lasted a few months now, however there is a creak similar to that which preceded the last failure starting to come from that vicinity again. If it fails again, I might just replace the whole crankset.
The crankarm wasn't properly tightened/checked by the bike builder. Grease the taper install new arm with a new nut or bolt. No need for Locktite.
Furious_E said:I might just replace the whole crankset.
That. Same happened on a prior MTB of mine. Replacing the crankset got to the root of the problem.
Well at least the bottom bracket or whatever the part is called that the crank arms actually bolts to.
The arm is much softer than the spindle (even steel crank arms), so unless the spindle has been bent just the arm & nut or bolt need to be replaced. We kept a wide selection of individual right/left arms in different lengths and colors plus hardware for common applications and did them almost daily at the bike shop for 25 years.
In reply to Ian F :
Exactly what i did as a broke kid. Certainly couldnt afford new cranks, so a strip of soda can to the rescue. I seem to recall it tightening things up enough.
If you're gonna try the soda can trick as a temporary measure.
1. wrap a piece on the spindle with grease on spindle
2. install arm with grease on inside of tapered spindle hole
3. Tighten nut/bolt
4. Use a block of wood and heavy hammer to smash arm on with one good whack
5. Tighten nut/bolt again
6. Do the whack thing again
7. Tighten nut/bolt again
It'll probably loosen again but will give you some time, YMMV. Left hand arms for Walmarty type applications are cheap so really, just buy a new arm & fastener.
Yep, square taper. Bike in question is the fixie from Walmart in the original black/red/yellow, circa 2012. I’m considering a new crankset. Although it will be funny when I will have spent more on parts than the original bike.
Also note that they gotta get surprisingly tight, like in the vicinity of 35 to 40 ft lbs - way over what is generally common "bike torque"
Crank bolts are one of the few fasteners I will always tighten with a torque wrench because they need to be deceptively tight to not back out or make noise.
I bought some cheap “vuelta” brand alloy cranks for a low buck fat tire build. Off amazon if i remember right. The stockers were steel so even being cheapos, it was a nice upgrade.
Good tips. I may retry it with a TQ wrench set at 40. Before I was just using a regular 3/8 ratchet and torquing it as much as I could before I couldn’t push back against the pedals spinning.
Pics of area where crank is mounted to bottom bracket spindle?
In reply to Rodulrich :
I’ll get some pictures up tomorrow, along with fully pulling the arm.
Yeah, the arm is pretty well mangled.
Double-check your replacement is the same length. I'm not sure whether cheap stuff is more prone to all being 170mm, but 172.5 and 175 are also very common crankarm lengths generally speaking.
That crankset looks like it weighs a ton. Now's the perfect time to replace it with something lighter. While you're in there, make sure the bottom bracket is turning freely; if not, service or replace.
Finally got to my LBS and picked up a new alloy crank arm and have everything reassembled. I made sure to tighten it down as much as possible. It’s at at least 40ft/lb. a quick shakedown run went well and I look forward to finally getting some real seat time again. I haven’t ridden much in the past 7 years.
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