I don't think it's a matter of the crank arm "walking" up the taper, so much as the crank arm relieving the portion of preload caused by friction between the spindle and arm interface. In the initially torqued state, the end of the crankarm is under quite a bit of compressive strain. The first couple of miles of hard pedaling would probably stress the joint enough to allow portions of the taper (the trailing edge) to either unload, or at least lower the load, and relax to a state further up the spindle. It wouldn't continue to move, unless you came back and re-torqued the mounting bolt. Jobst's contention was that it was possible to split crankarms by repeatedly "snugging up" the mounting bolt, progressively pushing the crank arm up a couple of thousandth's each round. (Many mechanics thought the mounting bolts were loosening, when in fact the arm had just moved enough to lower the tension on the bolt.) In contrast, he tried splitting the arms by just torquing the bolts to failure all at once, which caused bolt failures well before the arms split.

Personally, I lube the spindle / taper interface, and torque the crank bolts on the higher side, using a weak loctite on the bolts to make sure they don't walk out at some point in the future. Once torqued, I don't touch them unless I'm removing the crank. Knock on wood, no problems yet.

I recently installed a SunXCD copy of the T.A. Cyclotouriste crank on one of my bikes. I mounted it onto an old (as in "N.O.S.") Specialized cup & cone BB. The crank arms didn't fit very far onto the taper, and I did have to check and retorque the bolts after the first few rides. My guess is that the aluminum was deforming to match the axle's taper. There was significant loss of bolt tension for the first few rides.

As we all know, the best way to avoid a mechanical problem is to carry the correct tool with you! I've seen my share of people sitting by the side of the road with loose crank bolts, so back in the 90's (?), I bought a Cool Tool, which has a 14mm and 15mm socket for your crank bolts (tough luck if you are using your 16mm Stronglight bolts)





.....but tighten the chain tool portion against the body before wrenching on the bolt.

It's a really clever tool for vintage bikes. Not very light, though!

Steve in Peoria

Way back, the guys who had trouble with crank arms coming loose most often greased the tapers liberally. The Official Campagnolo mechanics of the day suggested very very little grease on the spindle tapers, basically apply it an then attempt to remove it with your bare fingers, the thin film left was enough. with the arm dry.

I have never had a crank arm come loose. A few seen coming in for repair way back, almost all of those required new arms due to deformation of the port or in only two cases, cracks radiating away from the spindle port, on those the arms were very well creased...

45nm comes to mind as a torque level. Don't ask me if I use one.

My brother in law's mountain bike had a left side crank arm that was always working loose. Without thinking about it too long, I put a dab of blue Loctite on the threads, torqued them down, and in two or three years, he's never mentioned it again.

I've done the Campy method of dry tapers and loctite on the bolt and a single torqueing. I've also done dry with no Loctite and retightening the bolt slightly several times after riding. Somewhat surprising, both methods have worked well. Seems I have faith in both methods, but not in one over the other.

If you haven't found a reliable method that keeps your cranks on, best carry a wrench. Murphy can rear his ugly head at any time, regardless of periods of reliability. On rides long enough to carry more than a simple tool kit, it would be good to have some means of snugging a crank bolt. I have a Sugino crank bolt socket with a rod for a sliding T handle that is a perfect portable tool. I've never taken it on long rides before, but I may consider it. Any ride that needs that level of repair capability also needs a chain tool and some spare links.
I commend the OP for finding a solution. It is amazing that something with the potential of coming apart even with a bolt in it can stay together without one.

See paragraph 3 of the Brandt article Installing Cranks by Jobst Brandt

Back in the old days there were no torque specs for crank arms, or if there were they never filtered down to us proles. Whether the taper should be greased or not was never discussed either. You torqued it until reasonably snug to a calibrated hand, rode some then remembered to tighten it again, always being careful not to over-tighten though that was never discussed either. I never had a crank come loose back then.

I dunno about that. Circa 1980 at my LBS we had a torque wrench and greased or not was discussed also. Can't speak to before that.

Perhaps I'm less a prole than I thought.

I had this happen on a shakedown ride after I resurrected a '74 Motobecane Grand Touring. It was pretty defeating when I noticed that the crank was also slightly damaged. I limped it home, and found the spindle threads were a bit stripped. I broke out a tap and die set and rethreaded them and fit a matching nut. It still loosened a bit on the next ride, but loctite and a thin lock washer solved the problem entirely.

When I started working on bicycles in the late 1960s none of the bicycle repair books or magazine articles mentioned torque values or lubricating the spindle taper. The reference material used subjective phrases, such as, "tighten firmly" and most recommended to re-tighten after a period varying from 25-100 miles.This still held true when I started working at the LBS in the early 1970s. The shop talk of the era was that Campagnolo's rather short "peanut butter" wrench was designed to provide the proper torque,without being over tightened (unless the mechanic was a "gorilla"). I don't recall recommended torque values appearing until circa 1980. I remember some references, such as Sutherland's, specifically mentioning that the spindle taper must be free of oil and grease.

I've intentionally avoided participating in this thread, because the last time I tried to discuss this topic, it turned into a bit of a 4-page firestorm over in the Bicycle Mechanics forum. I'd rather not get into it again. Look that up if you're curious.

But I will point out that Barnett's, Sutherland's, Park Tools, Campagnolo, Shimano, and the JIS all recommend clean dry installation on square tapers. There are excellent reasons for this that have nothing to do with lore, tradition, superstition, or religion. If you choose to ignore their advice and lubricate your tapers, I highly recommend you understand the implications of doing so, and more highly recommend that you always use a torque wrench when installing the crank bolt or nut.
Using a torque wrench, by the way, is the far more important part of Brandt's advice on the matter that is almost never brought up. Most everyone reads the part about lubing the tapers, but don't read or understand any farther. His larger point is that the much more significant risk to crank tapers is under- or over-tightening, not lubrication or galling.

I certainly don't want to start any firestorms here, but could you elaborate on those reasons for not greasing? As far as I know, the only one that seems to hold any water is the fact that greased tapers will reduce the friction, allowing greater movement of the crank on to the taper for a given torque value. (And theoretically allow for splitting cranks from over torquing -- Jobsts experiments, along with Jan Heine's seem to dispel this idea, at least for quality cranks. https://janheine.wordpress.com/2012/...not-to-grease/)

As for downsides, I'm sure you've seen spindles with bits of aluminum stuck to them, and tapers with torn up surfaces from galling. I can't imagine that repeated cycles of that can be good for the crank's socket over time.

Ultimately, it's important to understand that it's the compressive force of the crank arm on the taper surfaces that allows it to transmit torque, not friction between the surfaces. In order to transmit that torque without deforming the socket, the arm must be tight enough that at peak load, the force on the trailing edge of the socket never goes to zero. (If it does, then the spindle and socket can rotate relative to each other, and you will see deformation of the leading edge of the socket.) What you really want for a "good" installation is a defined amount of interference fit -- i.e. the taper needs to be driven a certain distance past "tight" into the socket. Torque values are really a very round about way of determining this movement, and vary greatly depending on thread condition, grease, taper condition, etc. Much better would be a spec calling for a certain amount of rotation past "snug". I know when installing most of my (greased) crankarms, I get around 1 to 1.5 turns before the torque required for further movement goes up dramatically. Once I hit about 20 ft-lbs, I only get perhaps 30 degrees more movement to 25 ft-lbs, then 30 ft-lbs might only be 5 degrees more.

In terms of "dangers" to the crank arm, insufficient initial torque is probably more worrisome than too much, followed by crank bolts that can back out, allowing them to fall off down the road. (Often goes hand in hand with insufficient initial tension, and probably the reason for the change from loose crank bolt washers to ones with an integrated flange. The integrated flange will tend to interlock with the crankarm surface, and help prevent loosening down the road.) That is why I always use some purple loctite on my crank bolts. It's weak enough that removal isn't too difficult, but it should prevent any potential loosening of the bolt down the road.

I'll try. But I would like to lay some groundwork first.

This topic does seem for many to be a quasi-religious. Meaning they seem to believe their one way is right in all places and times, and all who disagree are idiots or infidels. I'm sure they are nice people, but it is not worth my time to argue with them about this sort of thing, and I will ignore them. Nothing personal. You do not seem like such a person, thankfully.
Another problem, even in text arguments, is that many people don't read others' posts fully before firing off their response. So let's not have any of that here, OK?
I enjoy to argue (meaning "have a fair if passionate discussion") about ideas, but I do not like to argue with people. So please keep in mind that if I take a position for or against or around your idea, it is not personal. It may even be rhetorical; I may not believe it myself.

And if you don't mind, I'm going to take this in small bites. I'm also likely to challenge some of your assumptions, and try to present some of my own when they are relevant.
It's rather broader than simply that, but yes, this is really the main reason. Perhaps the only one. But it's a really significant one; how many such do you need? It has practical ramifications as well as engineering ones.

Rather than go into them now, let me start with this: For establishing a general rule, I am willing to trust in aggregate my named "authorities" over the relatively few exceptions that are usually offered as counter-examples. I am, in the same way, quite content to allow for such exceptions. When manufacturers make a specific recommendation for their cranks, I say you should follow it. I am willing to assume they, like others who may recommend differently, have done their due diligence, and have their own reasons for being an exception. General rules and recommendations are only general; they are not absolute. But they are to be followed unless there is specific contrary instruction.

As to the weight that I give to the consensus expressed by Barnett's, Sutherland's, Park Tools, Campagnolo, Shimano, and the JIS, versus Jobst Brandt, it seems so obvious I really feel little need to explain it, even though I shall. (Is there really anyone--who's not a manufacturer--who disputes a general rule of dry installation who doesn't either base their belief on, or justify it--incorrectly, if you ask me--with Brandt? Honest question. It always seems to come back to him or Sheldon Brown, who was basically quoting Brandt.)
The manufacturers and their organizations (Campagnolo, Shimano, and the JIS) all have literally decades of experience and millions of data points upon which to base their instructions. And it's not just "well, that's the way we've always done it." Most of the JIS bicycle specification covers durability tests and their protocols, not dimensions. And I say (with only mild humor) that it is pretty compelling when Campagnolo and Shimano agree on anything.
Barnett's, Sutherland's, and Park Tools, as educational organizations, are compilers and testers of each also have decades of compiling their own and others' experiences. They also all have close collaborations with the entire industry from mechanics to engineers.
In other words, any one of these sources has "big data," enough almost to make a general rule. Taken together, they have a mountain of it. It's a questionable mechanical practice to stack one's anecdotal experience against a mountain such as this. Mechanical things don't care what you believe.

Fools rush in, so let's deal with the elephant in the room. In the case of crankarms and bottom brackets, Jobst Brandt, for all his acknowledged genius and expertise, could not possibly have had a sample size that is remotely statistically significant compared to all these organizations' cumulative data. And as we all know (and many love him for,) he was not above using strong if occasionally faulty rhetoric to dismiss those who dared to challenge his conclusions. IOW, he was not always a good example of how to carry on a conversation. I think it's fair to say that his conclusions should be able to stand on their own without having to resort to his rhetorical stance, and mimicking that stance does nothing to settle his or anyone's conclusions. I don't dismiss them out of hand by any means, but I do feel compelled to take them as only a bit more than one very intelligent man's opinion, based on relatively anecdotal experience compared to the mountain of data of these other organizations.

Neither of those are conclusive, but for different reasons.

The crank-splitting argument is a straw man and I feel no need to counter it. Cranks crack from fatigue, not over-tightening. Any crank that does crack from over-tightening would have to have an internal flaw and/or be of very poor materials and engineering. The real problem is that we know nothing about Brandt's test protocols, if there were any, or his test parameters, or his sample size, or any of that science and engineering stuff. We have, as far as I can tell, only his relating of his experience as a conclusion. If we have otherwise, please let me know where I can read it.

As for Jan Heine's experiment, it appears to be a sample size of one, perhaps a few, and for a relatively rare sort of crank (namely with a forged taper.) Given that the only other crank tested was a Campagnolo C-Record (without dispute a "quality" crank) which has explicit instructions NOT to grease the taper, it is faulty to extrapolate towards any general rule about as vague a category as "quality cranks." (Jan does not specify whether he greased the taper for the C-Record crank, but if so, his experiment might support Campagnolo's dry taper recommendation....) Ultimately, Jan's advice is clearly meant ONLY as a specific recommendation for his Herse crankset, nothing more.

I'll take a break now, but will continue later.

Thank you for putting together such a polite, well reasoned statement of your position. I reserve the right to disagree with parts of it :-), but I appreciate the dialogue.

You are correct, that Jobst Brandt's writings on the grease / no grease debate are the goto reference / explanation for the majority of us "greasers" :-) I never met him personally, but I find the majority of his positions to be fairly plausible from an engineering point of view. As a person, he strikes me as having been "difficult" to say the least. Unlike him, I really don't care to prove others wrong. I'm generally satisfied in explaining my position, and letting others take that as they may.

Regarding the recommendations of Sutherlands, Park Tools, Shimano, et al, where we differ is that I place less stock in their "institutional wisdom." Sadly, most people, including engineers, really don't critically analyze things they "know to be true". (I'm as guilty of this as anyone.) While modern day manufacturers are quite concerned with fatigue testing (Thank you, product liability lawyers), most of the lore regarding square tapers was firmly in place by the 1970's. Back then, bicycle and component manufacturing and design wasn't heavily engineered and tested the way cars, or particularly airplanes were. Most bicycle and component design was an iterative process. Build something that looked "good", then either beef it up if you had failures, or whittle stuff away until you did. (This is a perfectly valid, if slow way to achieve an optimal solution. Fancier, modern methods just get you close, faster.)

Jobst's conversations with engineers at crank manufacturers back in the day revealed their concern that initial over-tightening would lead to cracking of crank tapers. As far as I can tell, this was the original rationale for the "no grease" position. Without testing it myself, ideally over hundreds of cranks, I can't say if this is unfounded or not. Jan Heine's testing of one forged crank seems to point towards it not being a concern, at least on his high quality ones. Perhaps on earlier cranks, with lower quality alloys, this was a legitimate concern. I haven't cracked any tapers either, but that doesn't really prove anything.

The other issue the gets brought up frequently, is that pushing the tapers too far on to the crank will cause them to grow over time, eventually ruining the crank. In order for this to be a practical mechanism, the crank taper would have to deform in a plastic manner. For quality alloys, this doesn't seem to be the case. (Low quality, cast cranks may well be soft enough, but I suspect they might crack first, as most cast aluminum isn't very ductile.). In contrast to this concern, un-greased tapers commonly cause galling, and scoring of the taper surface during either installation or removal. I've seen several tapers that have been chewed up in this manner, resulting in large pockmarks and low spots that reduce the overall contact, and could well result in taper growth if installed too many times.

Lastly, and to add to what I said earlier in response to randyjawa's question: I am just about positive that Jobst was correct about the cranks squirming further up the spindle after some initial use. I have verified, as I'm sure you have too that a properly torqued crankarm, if checked again after a dozen miles will take another bit of rotation of the crank bolt to get it back to the earlier torque level. The only plausible explanations for this are either: a) the crank arm has moved slightly further up the spindle, reducing the tension on the crankbolt, or b) the crankbolt has loosened slightly. What makes b) seem unlikely, is that this mysterious loosening only happens in the first few miles, then doesn't proceed any further. I can't think of any mechanism that would let the bolt rotate several degrees initially, then stay put for any additional thousands of miles. This suggests very strongly that a) is indeed correct.

I totally agree that the manufacturer (the one who did the testing and who has to maintain quality control of their product through periodic testing among many other duties) is going to be able to provide the best advice for how their products are best installed and maintained. Their best torque value will be based on either lubricated or dry assembly, i.e. what torque value worked best with that particular method of assembly.
I've known certain brands of cranks that were susceptible to cracking at the left crankarm square taper area, and it became known that they tended not to crack if torqued only once instead of periodically.
The bolt tension that exists immediately after torqueing the bolt is not the same value as after the bottom bracket has exerted torsion on the crankarm through the taper on certain cranks that simply cannot sustain quite that level of bolt tension over time without creeping up the spindle tapers. Some Shimano cranks with visibly more metal in this area may actually sustain the full tension value of the freshly-torqued bolt in use over time, but some do not, as can be felt by the bolt turning further each time that the bolt is torqued. Some cranks seem able to take it, and some (usually the lighter ones with less metal surrounding the spindle) can not.
Even some Shimano cranks that came after the earlier Deore cranks of the late 80's and early 90's would tend to walk up the spindle, and at one point Shimano began installing steel stop rings on their bottom brackets so that at least the drive side crankarm would not move significantly over time relative to the front derailer. And there is another issue having to do with how much twist is occurring along the tapered ends of the spindle inside of the hole in the crankarms, something that is much exacerbated by riding over rougher surfaces or jumping the bike with the cranks horizontal, as this definitely has the effect of relaxing the bolt's tension as more flexing movement occurs between the spindle and crankarm.

I'm glad we don't do firestorms on this sub-forum, because this kind of discussion is a lot less tiring.

My takeaway is that I'm going start installing crankbolts with a little blue loctite, continue to not carry a 14-mm socket, and optimistically assume that I will never have another loosened crank arm. Given that I've only had it happen two or three times in the last 40 years without loctite and am now 64 years old, that seems like a good bet.

I'm also going to continue to put a very light film of grease on crank tapers, mostly because I have some concern about galling. I have seen a few badly galled crankarm assemblies that were presumably ungreased, but have never seen a problem of any kind that I would attributed to the use of grease. Shimano obviously knows a lot more about it than I do. I'm not sure why galling is not a concern for them. (I would add the United Bicycle Institute to the list of authorities who favor the no-grease method of assembly).

I insist that my method is correct. I insist that dry assembly is also correct.

See Kipling, Rudyard: Poems - 'In the Neolithic Age'

I have a hard time believing that after I've been handling a spindle and cleaning and greasing BB bearings and all the stuff that the taper doesn't have at least a little inadvertent grease. Unless you, which is to say I, clean it with alcohol, wiping it off is not going to remove all the grease.

I bought an XT crankset circa mid 90's which had four factory-applied "worms" of grease inside of the square holes, one on each flat. By this time, as I mentioned, Shimano was adding a steel stop ring to their spindles on the driveside which prevented the chainrings ever moving in to far to where shifting might be compromised by the front derailer cage not being able to pull far enough inward (starting to become an issue with the 1-3/8" seat tubes coming into vogue). This model XT crankset featured a removable spider and was the last before they went to Octalink. It had more metal around the square holes than did the preceding 8s compact XT crankset.

I was wondering about that, too.

Doesn't the likelihood of galling increase over time if you don't remove the cranks from the spindle? So removing them frequently enough mitigates that risk. And to my thinking, which could be wrong, this is why torquing the bolt properly matters more than whether or not you have grease on the spindle.

Moving metal parts or interfaces generally have a film of protective wax or oil on them to prevent rust in transit. It is not generally intended to be used as a functional lubricant.

While Shimano (unlike Campagnolo) give no explicit instruction to degrease the taper prior to installing the cranks in their tech docs, they do explicitly instruct that grease be used on the threads of their BB cups: "Apply grease to the bottom bracket before installing it." With a pictogram of a little grease tub and an arrow pointing towards the cup threads.

As no such explicit instructions are given for greasing the tapers, I infer that they do not want that.

If, however, a crankset came factory-prepped with grease in the tapers, I would use it. Again, I am open to exceptions when manufacturer-specified.

Galling, or at least localized metal removal, is something I have seen from time to time, and I had suspected that it was due more to corrosion than to the surfaces sticking to each other.

I could be wrong about that though, since an aluminum piston that seizes inside of an engine's ferrous cylinder (albeit at high temperature) does leave streaks of aluminum on the cylinder wall that must be dissolved with hydrochloric acid to restore the smooth iron surface.

Certainly grease might reduce corrosive interaction between the spindle and crankarm, and thus might be why Shimano did commence putting the grease in their final run of XT cranks.
Or perhaps it was because crank bolts are so often under-torqued by less-skilled installers, and grease would allow more of an interference fit to develop with whatever level of torque was applied. I suspect the latter.

I think it takes a lot of movement to cause galling between such dissimilar metals, mainly because the aluminum very quickly develops a thin film of oxide that acts a lot less like metal. But where greater motion and thus relative surface speed from the twisting of the spindle's ends occurs (as when mountain biking), that oxide film might have proven to be insufficient, though in my experience I have yet to have seen any examples of where apparent galling caused an actual problem with the fit on the spindle. At the point where bolts bottomed out on the end of the spindle, a bit of grinding work on the end of the spindle restored the full effect of the bolt tension.

Since this is an exceptionally civil forum, I guess I'll throw in my two cents. Normally I avoid this subject.

I agree entirely with Ghrumpy. Best to follow the manufacturers' recommendations. Campagnolo, Sutherlands, and many others already mentioned recommend no grease on tapers. As a general practice, I wipe the tapers clean, grease the bolts and washers, and fix the cranks with about 25 ft/lbs (or whatever the manufacturer recommends). Phil Wood recommends grease. I have a Phil BB on my Mercian, and that spindle was greased. I also prefer a thin film of grease on Stronglight BB. Can't remember how I came to that conclusion, but it works. Most others 'dry'.

Residual grease is irrelevant, and IME it makes no difference if you clean the spindle with solvent or simply wipe it off with a rag. What can sometimes cause a problem is a spindle that is heavily greased. However, that will not lead to the arm(s) coming off it is properly tight. The main issue is that sometimes it will creak and be annoying. So if you prefer to grease your tapers and it causes you no issues, go ahead, I don't care. Again, the main reason crank arms fall off is that they are not put on tightly enough initially.

Before the wisdom of the Interwebs and during the dark ages of square taper bottom brackets, this was all common knowledge. When you are a mechanic and have 12 repairs on the board for the day, as well as 2 or 3 assemblies, you really don't have time for theorizing about force vectors. You have to be pragmatic. If it works, it gets done that way.

That's the thing -- the instructions are so specific as to whether to use grease on the cups (ixnay on the plastic ones!) and exactly what torque range to use when installing, that by not saying anything about the tapers, I've wondered if they don't think it matters that much in the long run.

I've read so many well-reasoned arguments in favor of dry or greased tapers over the years that I gave up and decided to shoot for the middle: a very very thin "wetting" of oil or grease on the tapers, torqued to the middle of the specified torque range, checked again after a ride or two, and then that's it. No problems to report like cranks coming loose or "riding up" from this practice, but then I only ride about 3000-5000 miles per year, so it might take a long time to find out if I'm ruining anything.