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Cranks keep falling off

Old 06-30-20, 08:36 PM
  #26  
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Originally Posted by RubeRad

Thanks, I will look some up, but I'm not optimistic about my ability to be persistent. ...
...stretching and loosening up the hips and pelvic muscles / ligaments can also improve your sex life. Think kundalini rising.
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Old 07-01-20, 02:18 AM
  #27  
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Originally Posted by RubeRad
They got loose, and eventually fell off. After repeated reattachment, they got loose and fell off at shorter intervals


I don't think it's CW/CCW, I suspect at the bottom of the stroke the crank is stressed inwards (towards the bike) and at the top outwards (away from the bike), gradually walking the crank off the spindle.
We agree. What is your pedaling style? Are you standing and pedaling hard frequently? Consider spinning the crank instead of mashing to limit peak forces on your drivetrain components.
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Old 07-01-20, 08:58 AM
  #28  
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Originally Posted by Unca_Sam
We agree. What is your pedaling style? Are you standing and pedaling hard frequently? Consider spinning the crank instead of mashing to limit peak forces on your drivetrain components.
Yeah, that suggestion never did much for me. Being fat and living among hills, I've never had a bottom gear that was low enough for spinning.

Also on downhills, I'm always standing, letting the bike absorb the chuff. Rigid Krampus, you know.
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Old 07-01-20, 10:00 AM
  #29  
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Originally Posted by Unca_Sam
We agree. What is your pedaling style? Are you standing and pedaling hard frequently? Consider spinning the crank instead of mashing to limit peak forces on your drivetrain components.
It is only once I started to spin that I developed IT and then piriformis issues. Sort of a repetitive stress thing, mashing actually reduced the issue.

I've always stretched. Don't know about the OP but not sure my out toeing is something that could ever be fixed. It seems more structural than muscular. Only real problem I have is when riding flats I have to be super conscious of keeping my foot flat on the pedal.

I would still give it one more go with a solvent cleaning than blue locktite. If that fails maybe red loctite is the solution. That and torquing the pedal whenever you check tire pressure.
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Old 07-01-20, 11:53 AM
  #30  
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I definitely don't stretch enough. I had always thought my duck feet were genetic/structural/inevitable, but since I read that it can be the consequence of long-term bad biomechanics, I am quite open to the possibility that I may have been wrong.
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Old 07-01-20, 08:42 PM
  #31  
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UPDATE!

I went in there to clean off the pinch bolts and put them back in with loctite (blue), and I (re)discovered what I didn't remember, which is that in addition to the pinch bolts, there used to also be a crankbolt, which fell out at some point and got lost. Here's a not close-up picture of the parts:


It's from this fleabay crankset.

I measured with my calipers, and the diameter to the tops of the threads in there read 18.21mm. The diameter of the flat (not chamfered) circular area that a bolt head could sit in was 26mm. Any educated guesses what the actual size/thread pitch is, and whether it's possible to find a replacement crankbolt? I'm going to contact the seller too, and ask if I can buy some spares, but I'm not optimistic.
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Old 07-01-20, 08:53 PM
  #32  
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Maybe a 'standard' M20 crankbolt might work?
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Old 07-01-20, 09:07 PM
  #33  
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eBay seller responded already, it's M19, which seems way rarer than M20.
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Old 07-01-20, 09:22 PM
  #34  
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The only M19 crank bolts eBay has are Titanium, $20 from China.

An Amazon review mentions success with this electrical component. I wonder if that hex head would fit in the circular recess, or if I could get a washer that would work
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Old 07-01-20, 11:49 PM
  #35  
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More quick reponses from the seller. He says that's not really a crank bolt, it's more of just a dust cap. So I'm back to the pinch bolts should be able to hold it on
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Old 07-02-20, 12:07 AM
  #36  
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Originally Posted by RubeRad
OK, so now with 3 different cranks on 2 different bikes, I have a problem with the left crank working itself loose and falling off.

I know correlation doesn't imply causation, but I think something's going on...

I use 20mm pedal extenders, and I weigh north of 240. Is that too much sideways torque for a left crank?

First case was an FSA crank on a BD Motobecane (I didn't touch the factory-assembled crank), where the left crank was held in by a torqued bolt (40Nm I think)

Second case was a Mr Whirly on a Krampus, with a more normal pair of side-pinch bolts.

Third case is the replacement crankset on the Krampus, also with side-pinch bolts.

Should I ditch the extenders, get even bigger pedals (currently Wellgo MG-1 or MG-3 I don't remember) and try to adapt my out-turned feet?

How far can I tighten those pinch bolts before I strip threads on either the bolt or the crank?
My older Motobecane 2010 the FSA crank would always fall off. It’s was a design flaw so I put lot loctite on the bolt and it held. I finally replaced it with a Shimano CX 50 crank around 105 quality with a Dura Ace BB. Reliable and flawless now. My newer Motobecane has the same FSA Gossamer crank but with a new design and it has been good for thousands of miles. The older FSA cranks are notorious for coming apart in route. I forgot I used the recommended torque on the older FSA and it came apart so I just went by feel and it was better then I added loctite the added pressure trashed the BB I said the hell with this and got a Shimano.
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Old 07-02-20, 10:01 AM
  #37  
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Interesting, I probably had the same or equivalent FSA crank on my motobecane.

Why would the added pressure trash the BB? In my recollection it's just a question of how hard the crank is attached to the spindle, and that shouldn't affect how the spindle rotates in the bb bearings
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Old 07-02-20, 11:59 AM
  #38  
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Originally Posted by RubeRad
Interesting, I probably had the same or equivalent FSA crank on my motobecane.

Why would the added pressure trash the BB? In my recollection it's just a question of how hard the crank is attached to the spindle, and that shouldn't affect how the spindle rotates in the bb bearings
The FSA Gossamer got rid of that pinch bolt. The pinch bolt is the weakness of the older Gossamer. Here is a pic of the 2016 FSA Gossamer that has no pinch bolt. Bolts directly on without that frikin pinch bolt that was a problem on my 2010. No problems with this crank which was surprising so far so good.

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Old 07-02-20, 12:07 PM
  #39  
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Originally Posted by RubeRad
Interesting, I probably had the same or equivalent FSA crank on my motobecane.

Why would the added pressure trash the BB? In my recollection it's just a question of how hard the crank is attached to the spindle, and that shouldn't affect how the spindle rotates in the bb bearings
Too much pressure on the BB bearings with the Hollowtech design the bearings on the outside of the bb housing. I guess it grinds more that is why there is a torque recommendation at the crank bolt. My old bikes that had internal bearings I would just crank down on the bolt hard so they wouldn’t fall off never had a problem. Probably more technical than that but that is what I have read in repair books.
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Old 07-02-20, 12:15 PM
  #40  
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My FSA was Afterburner/MegaEXO and the crank-securing system was branded 'NBD'. FSA customer support was very supportive and sent me a replacement crankset, which I installed with a torque wrench, and I rode that for a while ok until I passed that bike off to my son, who is not fat, and who doesn't use extenders.
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Old 07-02-20, 08:33 PM
  #41  
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OK, it's all put back together. Spindle splines, crank splines, crank bolt holes, and bolts all cleaned with alcohol, dried, loctited, put back together. Left-crank pedal extender removed (my left foot is not as bad as the right anyways). I also happened to need new brake pads, so I put those on and rode around bedding those in until I could smell 'em. The bike rode fine, and the missing pedal extender didn't even bother me (much, my whole body position is adjusted so the insides of both of my knees are sometimes touching the seatstays)

fingers crossed...
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Old 07-03-20, 01:09 PM
  #42  
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I also had an FSA crankset where the bolt wouldn't stay tight. After 10 years of it I finally gave up and replaced it with Campy to match the rest of the build.
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Old 07-03-20, 01:46 PM
  #43  
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Originally Posted by RubeRad
OK, it's all put back together. Spindle splines, crank splines, crank bolt holes, and bolts all cleaned with alcohol, dried, loctited, put back together. Left-crank pedal extender removed (my left foot is not as bad as the right anyways). I also happened to need new brake pads, so I put those on and rode around bedding those in until I could smell 'em. The bike rode fine, and the missing pedal extender didn't even bother me (much, my whole body position is adjusted so the insides of both of my knees are sometimes touching the seatstays)

fingers crossed...
20mi today, and things look good -- for now. I didn't even mind having no left extender. I might even try takin goff the ight one, or looking for shorter than 20mm
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Old 09-19-21, 05:59 PM
  #44  
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The latest development in my crank saga:



It seems the extra leverage of the extender, plus my fat ass, was too much for the aluminium in this $50 crank. Checking my eBay history, I bought that in Jul 2019, so it lasted a little more than 2 years. Not very impressive.

I've been fine without the left pedal extender, but my right foot is more twisted than my left, ditching the right one would be annoying. I see on eBay I can buy a 16mm extender instead of the 20 that's on there now. And I'll try to put my old Mr Whirly back on, hopefully that's more durable
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Old 09-19-21, 06:42 PM
  #45  
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Moving the failure point to a different spot counts as progress to me.
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Old 09-19-21, 09:27 PM
  #46  
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lol from the bolted joint to the 'solid' aluminum?

Note again the extender seems a contributing factor, too much sideways/outwards leverage at the top of the stroke (and too much inwards at the bottom). On this first test ride with new tires, it was the first time in a long time I was able to climb standing and not lose traction, that's probably more stress on the crank
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Old 09-20-21, 01:05 AM
  #47  
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Looks like I'm a late arrival to this thread, but I'll throw my 2 cents worth in:
1. Yes, pedal extenders are going to exacerbate this issue. No, larger pedals instead won't help. It doesn't matter if it's a small pedal on a long extender or a large pedal on no extender if your foot ends up in the same place anyways.
2. It's the NDS (left) arm each time because the left arm to spindle interface sees bending load and drive torque from the left pedal at the same time. The drive side crank to spindle interface sees this torque as well, but not at the same time as it sees the bending load from forces on the right pedal. Right pedal torque about the spindle goes out the sprocket, not onto the crank. TLDR, the left side has a harder life.
3. It's possible the crank lets out a few creaking sounds before it can be felt to be loose, that's an indication something needs to be done.
4. While you shouldn't really need loctite (unless specified originally), I'd consider blue. I wouldn't use red. If you're breaking loose blue loctite in this application something is already wrong.
5. Not surprising that it happens faster after the first time. As soon as you ride on it loose for even a short distance the spline interface will be worn and no longer fit correctly. Poor fit will turn quickly into loose cranks.
6. On pinch bolt designs (eg. newer Shimano) the large axial nut just serves to snug things into place before the pinch bolts are tightened. The pinch bolts are actually what holds everything in place. Once those are loose it won't matter what the large nut is doing.
7. I'd stay away from things with a GXP design. Just my experience, but they seem to like coming loose more than others.
8. I wonder if there are any appropriate options that put the joint in the middle like the Campy UT. Seems that might be less susceptible to this.
9. That's an impressive break in the latest image. That's a good way to crash with a sharp metal thing bouncing around. Jobst Brandt, famous for breaking cranks, would regularly inspect for cracks. It may be worth doing that, and also checking installation torque at the same time*.

*There are some downsides to constantly re-tightening square taper cranks, as in they'll split eventually, but designs (example Shimano) with non-tapered splines shouldn't have an issue with that.
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Old 09-20-21, 09:01 AM
  #48  
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I replaced my FSA SLK early model crank with a Campy Chorus UT compact. I got tired of tightening the bolt on the FSA only to have it loose again at the end of the ride. I did this about 2 years ago and haven't thought about the crank since. I have all the tools if anybody wants to come to Brooklyn to have it done, but usually the hardest part is getting the cups off and may not have the one that fits your particular crank. The Campy and FSA used the same tool luckily enough.
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Old 09-20-21, 11:54 AM
  #49  
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Originally Posted by jccaclimber
Looks like I'm a late arrival to this thread, but I'll throw my 2 cents worth in:
1. Yes, pedal extenders are going to exacerbate this issue. No, larger pedals instead won't help. It doesn't matter if it's a small pedal on a long extender or a large pedal on no extender if your foot ends up in the same place anyways.
2. It's the NDS (left) arm each time because the left arm to spindle interface sees bending load and drive torque from the left pedal at the same time. The drive side crank to spindle interface sees this torque as well, but not at the same time as it sees the bending load from forces on the right pedal. Right pedal torque about the spindle goes out the sprocket, not onto the crank. TLDR, the left side has a harder life.
4. While you shouldn't really need loctite (unless specified originally), I'd consider blue. I wouldn't use red. If you're breaking loose blue loctite in this application something is already wrong.
Thanks for all that detailed info. 1. yes that is obvious to me (now), physics is physics, leverage is leverage. 2. As you noticed the most recent time was DS. 4. The current broken crank is on with blue loctite, I haven't tried yet to see how hard it will be to get off. I'm not sure I have the tools to remove it destructively if necessary, but it certainly isn't worth saving. I'll take off the chainring and keep it, but atmo I don't have another crank with the same BCD.

My hope is, if I can get the Surly Mr Whirly back on, with no pedal extenders, it will be solid for me, even though I had worked the left crank off it before (with/because of the extender)

If anybody knows of a PT regimen to straighten duck-feet, I'm interested.
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