sloppy robot

boston trevor and i had a to grease or not to grease offshoot discussion the other day.. and both came up with evidence claiming to do both.. so now im curious..the Miche crank installation instructions offer this up..

"fit the packing onto the central movement pin which does not require any kind of lubrication"

(im guessing the translator doesnt build bikes..)

so.. i want more opinions on this.. what about you shop folks that always have good tips.. grease it up? or fly dry...

dolface

must. resist. urge. to. make. jokes!

sloppy robot

jokes are welcome.. although its such a lob, they better be good

jasonyates

Stop thinking and start doing. What is the worst thing that could happen either way? (That's not a rhetorical question either -- let me know if some kind of disaster could occur from doing it one way or the other.)

sloppy robot

ive been doing for 25 years now.. dry.. but ive done other things in my life wrong for 25 years.. so i just was seeing what others thought...i dont know of any disastors either way.. i think itd be more of a long term difference

46x17

Freewheel SF tells to grease shimano square taper cranks and all the splined stuff, but not to grease any campy tapers. That is what the manufacturers tell them. If one is better than the other I don't know. I never had any campy bb or crank so I have greased all the spindles I ever owned. Best to follow manufacturers instructions in order not to void any warranties. Not sure what Miche calls for - I guess not to grease since it is italian (kinda sounds that way from the instructions too)?

filtersweep

I always grease "metal on metal"- but consider this- it really isn't for "lubrication" per se. When you grease a seatpost, you really aren't lubricating it, since they aren't really moving parts relative to one another. It is greased to hopefully prevent bonding.

Per the dictionary:

cavit8

Like 46x17, I always grease my spindle... Spindle and crank arm is a force fit, so as per filtersweeps comment, lubrication doesn't allow anything to move. The only reason I use it is that it may help the crank arm move more easily up the spindle as I tighten it down.

bostontrevor

filtersweep: it is for lubrication. When you're installing the cranks, the spindle and crank move relative to one another.

My argument is that greasing the spindle allows the crank to seat without getting caught up and galling on the spindle. This means it will seat to the proper depth at the proper torque value.

The counter claim goes: it's not necessary to grease alu cranks as they act as their own lubrication (btw, how come this argument doesn't fly when it's a seatpost or stem?). Some even go so far as to say that grease will somehow cause you to overtorque the cranks or something and split them. I don't really understand the argument and I don't think there's any logic to it. Properly installed cranks can't be overtorqued. The overtorqueing risk is to the fxing bolts themselves.

And the Campy-goes-dry while others are greased... that's a crock. It's one or the other. I simply don't buy that the TAPER has a single thing to do with it.

Slartibartfast

grease has solved or made easier most of the difficulties life has thrown my way ... make that grease AND beer. this is doublely true for bicycle maintainance.

endform

I was told by my LBS not to grease as it is easy to push to the crank too far onto the spindle and thus strip your threads or worse, mess up the spindle/crank.

filtersweep

Sure, but only when you are installing. It isn't like it won't install without the grease (it isn't like lubing a bar so it slides easily into a quill stem). They shouldn't me moving relative to each other when you pedal.

I think it goes back to having two different alloys in contact with each other- a steel spindle and an aluminum crank.

bostontrevor

Yes, they're not in frequent motion, but it is an important lubricant. Otherwise metal-on-metal friction can prevent proper crank seating. Which brings up endform's shop:

First of all, greasing the spindle has nothing to do with fixing bolt torque. Seating the spindle deeper doesn't somehow change the laws of the cosmos so that 350 in-lbs of torque is no longer 350 in-lbs of torque. That's independent of how deeply the crank is seated or even whether the crank is installed at all. If the bolt is going to strip at 350, it will strip no matter what is or is not installed on the spindle.

Secondly, overtorqueing a fixing bolt doesn't strip the threads. The head twists off, trust me. Already, I'm suspicous of the provenance of this advice. It sounds like hoodoo voodoo to me. But let's think about the implications of the second part too.

What they're saying is that lubricating the interface between the crank arm and spindle will cause the crank to seat deeper than it's supposed to and somehow damage the crank. Where is extra force that's damaging the arm coming from? After all, the force that's keeping the arm on the spindle is the 350 in-lbs of torque on the fixing bolt. That's going to translate into force between the spindle surface and the crank's spindle hole. That force will not vary depending on how deep the crank is seated, it's solely determined by the torque of the bolt.

Not only that, but the shop is telling you that proper installation of the arm means that metal-on-metal friction should keep it from seating to the depth it would seat to in the absence of such friction. Do they also explain how additional miles will prevent those points of friction from breaking down and allowing the crank to move down on the spindle and thus loosening up?

white lobster

I've installed thousands of cranksets with greased spindles, and more thousands without greased spindles. The only functional difference I have found applies only to low-end Shimano MTB cranksets. On these cranks, a greased spindle (for some reason, these cranks came pre-greased from the Trek factory) meant that the cranks would draw too far onto the spindle. As a result, the end of the bb spindle would wind up flush with the outside edge of the crank's spindle hole. All of a sudden, instead of tightening down against the crankarm, the bolt would be tightening against the edge of the spindle. If you applied the correct amount of torque, the bolt head would almost always pop off.

Shimano's fix for this problem was to install a steel collar on the bottom bracket spindle (not sure if they still do this) on certain cheap bottom brackets to stop the crank from drawing on too far. In my opinion, this was a hack solution, since you always found yourself tightening the crank against the collar, instead of snugging the crank against the spindle taper. Thankfully, though, no more bolts broken on $250 bikes.

Bostontrevor has a point: Crank bolt tension is measured in a direction that is parallel to the bb spindle. But the important tension at work here is the force of the bb taper against the inside of the crank hole. This force works in a direction perpendicular to the bb spindle. So the bb taper is basically an inclined plane.

As to the argument that grease doesn't change this perpendicular force provided the parallel force is the same, I'm not sure I agree. If you're pushing something up an inclined plane, you'd be able to push much more weight if the plane was greased.

bostontrevor

That's because the grease reduces friction. (Hopefully you have somewhere else to stand than on the greased part or you're going to have a real hard time pushing anything up that plane. ) It doesn't change the stress on the thing you're pushing up the plane due to gravity.

The damage to the crank is not from the frictional forces--except the galling that may occur when no grease is used--but from the pressure between the two surfaces. This pressure is present even when the parts are not moving relative to one another. In fact, it's this pressure that keeps them stationary. The grease simply reduces the friction when they're moving.

A somewhat imperfect analogy is to think of the weight of the thing you're pushing up the inclined plane. You can increase the weight of that something until the point at which it can no longer support itself against the force of gravity. Gravity draws that something downward and the surface on which it rests exerts an equivalent resistance to hold it in place. This pressure causes the something to break down similar to what would happen if the pressure at the spindle/crank interface was too high.

Whether the inclined plane is greased or not has no relation to the pressure at something/plane interface. That's determined by the mass of the somethnig and the force of gravity.