I asked the same question...

..when I was building up my bike and got conflicting answers. I ended up greasing the tapers and have had no loosening over the last couple of years. I just re-torqued about 2 months ago and the wrench turned less than 1/8 of a turn, so the crankarms have been pretty solid (RF Turbines on a UN72).

 

I will quote.................

........from the RaceFace info sheet that came with my cranks. It's on my desk as we speak -

"We recommend applying a film of waterproof grease to the BB spindle flats before installing RaceFace cranks to help prevent corrosion that can occur between the cranks tapers and the BB spindle"

That being said, I've installed dozens of cranksets over a lifetime and I've done them both ways and have not had one problem caused by grease or the lack of grease.

 

I just remembered...

At the shop of which I spoke, we also put a dab of blue Locktite on the spindle before re-installing. I've never heard of anyone else doing that.

The corrosion issue seems reasonable, I wonder if the Locktite might help with that, as well.

 

No grease on square taper, grease on splines

Ask any pro mechanic and it's no grease on square taper bb axles, but do put grease on splined type axles (shimano, isis and bmx type) to prevent creaking. Square tapered axles are a press fit and there is some deformation of the crank hole when tightened. Greasing may allow the crank to be pressed on too far.

Regarding corrosion, that may be Race Face's stance, but most axles are plated/treated so corrosion shouldn't be a problem.

 

Ask any pro mechanic and it's no grease on square taper bb axles,...Square tapered axles are a press fit and there is some deformation of the crank hole when tightened. Greasing may allow the crank to be pressed on too far.

ROTFLMAO!!!

I love myths and legends. They're hilarious.

Here's some info to consider (myth proponents do not read):

Subject: 8f.11 Installing Cranks
From: Jobst Brandt <jobst.brandt@stanfordalumni.org>

> My cranks get loose, quite quickly too; over about 10 miles or so
> from being solid to flopping about in the breeze. Any suggestions?

Your cranks are ruined! Once ridden in the "floppy" mode, the square
taper in the crank can no longer be secured on the spindle. Get some
new cranks and properly tighten them after lubricating the tapers.
Proper tightness can be guaranteed only by torque wrench or a skilled
mechanic. The second of these is less expensive and you might be able
to get a demonstration of what is tight enough.

The admonition to not lubricate the tapers of the crank spindle seems
to find life only on bicycle cranks, of all the machines I have seen.
I have pursued the "dry assembly" instruction by talking to crank
manufacturers and discovered that they apparently had warranty claims
from customers who split their cranks open. It is easy to prove that
cranks cannot split by over-tightening simply by attempting to do so.
It is not possible to split a major brand crank this way, the bolt
will fail first.

Crank failure from "over-tightening" is caused by the re-tightening of
previously properly installed cranks. Once installed, a crank always
squirms on its taper, and because the retaining bolt prevents it from
coming off, it elbows itself away from the bolt and up the taper ever
so slightly. This can be detected by the looseness of the retaining
bolt after the bicycle has been ridden hard.

Grease in this interface does not affect performance, because only the
press fit, not friction, transmits load from crank to spindle. As any
bicycle mechanic can tell you, crank bolts are often appreciably
looser after use, the left one more so than the right. This occurs
because the left crank transmits torque and bending simultaneously
while the right crank transmits these forces one at a time. The right
crank puts no significant torque into the spindle. Either way, the
looseness occurs because loads make the crank squirm on the spindle
and the only direction it can move is up the taper, the retaining bolt
blocking motion in the other direction.

Regardless, whether grease or no grease is used, in use the spindle
and crank will make metal to metal contact and cause fretting
corrosion for all but the lightest riders. The purpose of the
lubricant is to give a predictable press fit for a known torque. If
the spindle is completely dry this cannot be said, and even with
marginal lubrication, some galling may occur on installation.
Lubrication is only used to guarantee a proper press because the
lubricant is displaced from the interface in use. Taper faces of
spindles show erosion and rouge after substantial use, evidence that
the lubricant was displaced.

"Dust caps" aren't just dust caps but retention for loose bolts. It
is not that the bolt unscrews but that the crank moves up the taper.
However, once the screw is unloaded it can subsequently unscrew and
fall out if there is no cap.

Because cranks squirm farther up the taper when stressed highly, the
unwitting mechanic believes the screw got loose, rather than that the
crank got tighter. By pursuing the crank with its every move up the
spindle, ultimately the crank will split. It is this splitting that
has been incorrectly diagnosed as being caused by lubrication. I have
never seen a warning against re-tightening cranks after having been
installed with a proper press fit. It is here where the warning
belongs, not with lubrication.

For the press fit to work properly, the pressure must be great enough
to prevent elastic separation between the crank and spindle under
torque, bending, and shear loads. This means that no gap between
crank and spindle should open when pedaling forcefully. Friction
has no effect on the transmission of torque because the crank creeps
into a position of equilibrium on the spindle in a few hard strokes.

Failure of this interface occurs when the press fit is too loose
allowing a gap open between spindle and crank. Torque is transmitted
by the entire face of the press fit, both the leading edge whose
contact pressure increases and the trailing edge whose contact
pressure decreases. If lift-off occurs, the entire force bears only
on the leading edge and plastic failure ensues (loose crank syndrome).
Tightening the retaining screw afterward cannot re-establish a square
hole in the crank because the retaining screw will break before the
spindle can exert sufficient stress to reshape the bore. Beyond that,
the crank would split before any plastic deformation could occur even
if the screw were sufficiently strong.

Because retaining screws could become entirely lose from squirming
action, especially if the press is relatively light, "dust caps"
should be used to prevent screws from subsequently unscrewing and
causing crank bore failure. Besides, the loss of the screw won't be
noticed until the crank comes off, long after the screw fell out.

The argument that the greased spindle will enlarge the hole of the
crank and ultimately reduce chainwheel clearance is also specious,
because the crank does not operate in the plastic stress level. At
the elastic limit it would break at the attachment knuckle in a short
time from metal fatigue, that occurs rapidly at the yield stress. In
fact, the depth of engagement (hole enlargement) can increase with an
unlubricated fit faster than with a lubricated one, because
installation friction is the only mechanism that reams the hole.

 

The admonition to not lubricate the tapers of the crank spindle seems
to find life only on bicycle cranks, of all the machines I have seen.

Very interesting - thanks for that, Pete. I certainly do consider Jobst Brandt a reliable expert source, and it makes sense the way he puts it. I've got The Bicycle Wheel, so I know just enough to know that when Brandt speaks, I should shut the hell up. I'm no engineer. I will henceforth change my ways, unless someone else has a brilliant debuttal.

Dunno how I'd convince that old boss of mine, though .

 

Theory vs applied

While I give Sr. Brandt props in the wheel engineering dept. (I'm sure he's brilliant to the extent he forgets where he leaves his car keys), I am basing grease/no grease off 20 years experience (and every one will have and is entitled to their own opinion - this is just mine). Here's what Park Tools website has to say on the subject:

Removal and Installation of Cranks (square spindle type)
Aluminum cranks typically do not require lubrication of this press fit. Aluminum by its nature is self-lubricating as it is covered with a thin layer of oxidation. Adequate torque is typically enough to keep arms from creaking.
Read more on square taper bb here: http://www.parktool.com/repair_help/FAQrCarm.shtml

ISIS DRIVE® and SHIMANO® Octalink (pipe billet) Spindle Crankarm Removal and Installation
a. Grease threads inside bottom bracket spindle. Grease splines on spindle.
b. Rotate pipe billet spindle so one spline aligns to top dead center, at the 12:00 position.
c. Position right crankarm on to spindle so arm points straight down at the 6:00 position. Place crankarm on spindle and carefully thread bolt into spindle. View opposite side of spindle and check that a narrow spline is aligned to top dead center. Threading should continue without resistance until crankarm visually covers spindle splines.
d. Tighten bolt fully. If possible use a torque wrench and secure to 305-391 inch-pounds.
e. Align left arm so it points directly opposite from right arm. Thread bolt into spindle and tighten fully.
Read more on splined bb here: http://www.parktool.com/repair_help/Pipe_Billet_Spindle_type.shtml

 

So I guess that you realize that your "Greasing may allow the crank to be pressed on too far." argument is nonsense? I've had cranks seize tight on bb spindles possibly due to the action of water and disimiliar metals causing corrosion. They were stuck on so tight that the crank puller stripped out the threads before the cranks would come off. A small bit of grease will prevent that.

 

pressed on too far might have been an overstatement

but I have worked on customer's bikes who do grease and some of these guys were the guys who constantly remove cranks to clean their bikes. After time, the crank bolts bottomed out on the spindle. If a=b and b=c, then of course a=c, right?

Just stating my preferences based on experience.

 

but I have worked on customer's bikes who do grease and some of these guys were the guys who constantly remove cranks to clean their bikes. After time, the crank bolts bottomed out on the spindle. If a=b and b=c, then of course a=c, right?

Just stating my preferences based on experience.

So if a rock is hard, and your head is hard, then your head is a rock?

I think that's less a function of grease and more of constant reinstalls. Every time you reinstall square taper cranks they have to go slightly further up the spindle by design, so you really only have a limited number of reinstalls. This is the reason I originally switched to Octalink and ISIS. Stiffness was just an additional benefit.

 

what type of grease ?

Hey ho folks , you may indeed want to consider just what type of grease you are proposing- typical lithium is soap based and will absorb water thus causing corrosion over time, Not good.
To me, I want the mating pieces as clean as possible. It is all a mater of perspective.

An assembler in a hurry , who is looking for consistant torque readings , and not neccessarrilly looking for long term may want to slather a lube on, but that is not in the best interest of the rider or the bike's cranks longevity.

The main theme to realize is that grease was not designed for this application and a product called anti seize is. "Grease " is shade tree, mechanics 101..
If you are going to use anything-use the proper application, copper based antiseize. And a very thin coat at that, one that looks every bit as thin as paint. Ultimately, in the best interests of the cranks, clean is best.

Happy trails, D. Douglas Fir sales@morningstartools.com

 

You ever strip the threads on a square taper crankset trying to remove it?