Cranks keep falling off
 

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?

So the bolts are working loose?
If so use locktite or regularly check the bolt torque. Don't wait till it is loose.
Try without the extenders but if you already know you need them then you do.
Bring a tool with you when you ride to check the bolts.
A good Allen key in the correct size and lenght. Longer ones are best.

I don't know if it's particularly the bolts, or if the splines are somehow getting rounded from being torqued one way at the top of the stroke, and the opposite at the bottom, and it eventually worms (not a typo) its way off. With the first two cranks, after the first fall-off I would put it back on and tighten it back up, and it would keep working loose, at shorter intervals. First time for this crank and it would be great if I could halt the pattern here.

Loctite is a good place to start though. I have some loctite blue and will put that on tonight. Maybe I need stronger than blue though.

:)

Are you talking about threadlocker on the splines (or in your case square taper), or the bolts? Never heard of E6000 glue, that says 'permanent'. If it doesn't work I guess I'm out just the cost of the glue. But if it does work, does that mean the crank could only ever be removed destructively?

Note: it is a known problem (i've seen it on other threads) that once a square taper gets rounded, it will always be subject to coming loose. But the interface on these cranks is not tapered, it's a straight cylinder with splines. I think somehow my weight + the extra sideways leverage from the extended pedals, is causing the crank to shimmy its way off the splines. I find it hard to imagine that the cylinder is getting a significant tapered deformation though.

Note also in a previous thread (about the Mr Whirly) I was advised loctite on the splines would not do what I hoped

:)

I just worked on a donated bike with those extenders. The left pedal was stripped out of the crank arm (square tapered). I blamed the extenders and I agree yours could be at fault.

...first, unless your left leg is both your dominant one, and there is a significant difference in how much downward pressure you can exert with each leg, I don't get why always the left crank arm.
Second, I only use pedal extenders on a couple of bikes, where there was no other way to gain enough clearance for the toe straps I use to clear between my shoe and the crank arms.

Third, I'm not certain what you mean when you mention your out-tuned feet" ? If you are pedaling your bicycle like this (heels pointed significantly inward, toes out), you will eventually cripple yourself if you ride far enough regularly. There is this whole art and science to adapting your own unique foot anatomy to the pedals that connect you to the bike. Pedal extenders are not the way you want to do this, except as a last resort. They can be used successfully to widen the Q factor everyone is always talking about, for people with wider pelvic structures and a natural spread between the feets that is on the wider side.

But yeah, I guess the pedal extenders might be contributing to this. I can't tell you much more that might help, because it's not something I have personally experienced. If you want to continue using the pedal extenders instead of trying to figure out a different way to alter your foot position in the pedal (it really is something you need to experiment with...that was the only way I finally figured out my foot pain on long rides issues), I guess there's always the option off finding some old bike with a cottered crank. Properly seated, those crank arms are on there for the duration.

Because the left arm is a separate piece attached to the spindle with bolts. The right arm/chainrings are all one piece with the spindle. Or welded maybe.


That's exactly it. When I stand with kneecaps forward, my toes point out. If I twist my feet so they point forward, my kneecaps point in. Before I got pedal extenders, I nearly crippled myself trying to ride with my feet rotated in, had to drop out of a group ride and hobble home pedaling with just one foot the pain was so bad. (Fortunately a couple days rest and some IT band work got me back with no permanent damage).

However, I have read in the book Supple Leopard, that for most people, out-turned feet is not an inborn, inherent trait, but a symptom of a lifetime of lazy posture and incorrect body mechanics. I do not doubt that at all, and if you have links for 'this whole art and science to adapting your own unique foot anatomy to the pedals that connect you to the bike' I would love to read about it.

OI use it for all kinds of things. but it requires air to cure like any silicone. I remember glued to panels of material together and in weeks the center never dried. but it is not permanent and you can usually peel it off with some work.

Shimano's recommended torque for the two pinch bolts on the NDS arm of their HTII cranks is 12 to 14 Nm or 106 to 122 in-lbs. I expect other similar cranks have similar specs. I've always tightened the pinch bolts on my HTII cranks to 110 to 115 inch-pounds and they have never come loose and I've never used threadlocker.

12-14 is not much, right? I recall on the FSA crank, which didn't use sideways pinch-bolts, but a single bolt inline with the spindle, that was like 40 or 50 Nm, which I did with a borrowed torque wrench, and it was Very Hard.

Lucky you. Obviously I've got bigger problems

...OK, I get it now. Damn new fangled technology. *ptoo*



...this body mechanics stuff is all over the internet. I've devoted a good part of my life in working at it, in order to salvage what I can after a lifetime of earning a living with my body in less than ideal circumstances. With out turned toes, generally what is going on in most cases is some shortening and tightness of the ligaments and muscles in the ankles, but probably also the hips. Knees, unless injured or other wise deformed, usually don't contribute to this sort of problem. But honestly your best bet is to either find a professional podiatrist who works in sports specifically, or maybe find an enlightened yoga teacher who can start you in some direction for gradually stritching out some of the stuff that is causing you to toe out. One of the many jobs I had before I went gubb'mint was as a farrier. It's a problem for many horses as well. Horses don't take well to yoga, so we used to custom make corrective shoes for them. Think orthopedic shoes for horses, and you have an idea of it.

Tai Chi is also helpful, but not without the stretching. If you just jump into some kind of movement exercise cold, you'll just reinforce your existing bad habits of movement

That Supple Leopard (the correct spelling of that word just doesn't seem right!) book asserts that for proper standing posture, your feet should be rotated inwards more than is natural for your body, so you feel like they are being 'screwed into the ground' (right foot rightie-tightie, left foot opposite)

.
...the Iyengar yoga people are big on standing poses. I grew up much like you, with my toes pointing out and always wearing my shoes out on the outside surfaces of the soles and heels. It wasn't until I started running seriously in my late 20's and had to deal with the problems I encountered from that, that I started down the long road of body mechanics and movement. (Yes, I know running is stupid. But many of us need to learn the hard way.)

If I could give you just one reference, I would. Unfortunately, movement and posture are remarkably resistant to correction through self study. My experience is that it is worth the time and money to seek out someone who actually has some experience and knowledge in this area. (And sadly, not everyone who hangs out a shingle knows what he's talking about.)

Very generally, tightness in the hips and groin,, that has developed over a lifetime of improper habit, translates into rotating the knees and feet outward, But just like with horses, you have to correct it gradually. Usually over a period of months and years. Just the way it is. But the yoga is good for you in so many other ways as well that, for me at least, it was worth the investment in time and money. You don't really figure out how badly distorted you are in some places until you are in a situation where someone with broad experience can show you what "normal" is.

Meanwhile, stufff like yoga classes are a thing of the past for now. So if you do want to work on it, try searching for Youtube videos using search terms like "yoga to correct duck feet" and "yoga to correct pronation/supination".

Good luck with this, and be patient, but persistent. Sometimes it takes a while to have an awareness breakthrough. Pain usually focuses the awareness in most people. :)

Yes, it's the extenders.

The crank interface isn't designed to do much more than rotate the spindle. Introducing additional forces outside of the roughly perpendicular pedaling motion seems like there best explain for the crank failures.

If you think of the pedal axle as a lever, shifting the locus of your effort away from the fulcrum (where the pedal and the crank arm are screwed together) will increase the sideways force on your spindle interface. Pinch bolts won't resist that force well. A typical crank bolt will, but over time I'd expect the alloy taper to deform enough to come loose.

Not a square taper in this case (I'm talking about typical MTB cranks with spindle permanently fixed to right crank, left crank bolted onto the splined spindle) but thx

QFT

Thanks, I will look some up, but I'm not optimistic about my ability to be persistent. I guess the first step is admitting I have a problem (and that duck feet are not necessarily genetically determined)

Yes, it's still your pedal extensions.

So do you think the leverage would have irreperably deformed the spindle? Or if I took the extenders off could I go back to my Mr Whirly crank?

I can't answer those questions without seeing it firsthand. The Mr. Whirly seems like a hybrid between an octalink and hollow-tech. The installation instructions make it clear that it's a 3 piece system, with the drive side held on by a crank arm bolt torqued to 50Nm (may as well be one piece, right?) The non drive side uses pinch bolts like a hollow-tech II crank, up to 10 Nm. Did the arms fall off, or just get loose?

What makes you think that you're stressing the crank-spindle interface in both the clockwise and counter-clockwise directions?

External tibial torsion with out toeing. I have had this since adolescence. Interestingly only on my right leg, not uncommon from what I have read. Everything I've read says it doesn't cause issues except on a bicycle or for yoga. Check that.

Everybody is different, you have to find what works for you. Sort of why I cringe when people talk bike fit. Personally I have to use clip less pedals to lock my feet into the proper orientation. I slide the cleat to the near inside of the shoe than rotate the toe in to be half way between where it wants to be and where it should be. Trying to force the feet parallel causes knee and IT band issues.

For your crank issues I agree with cleaning every bit of grease than use some blue loctite. If that doesn't hold I wouldn't go with red, that can be near impossible to ever remove. I would instead look into a new crankset.

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.

knees are ok so far, but IT band issues got me onto extenders which solved my problem.

This is the new crankset. I don't want to be buying new cranksets every 6 months