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Having to replace a non-drive side square taper crank, which kept working its way loose - I'm guessing as a result of the crank bolt not being done up tight enough and the BB spindle deforming the square hole.
New crank's snugly on - question is, how tight do I want to be doing the crank bolt up? I don't have a torque wrench, so the answer must come from the following options:
a) fairly tight - tight as I can by hand with a decent 8mm hex key
b) pretty tight - using body weight to tighten hex key as much as I can
c) b'stard tight - with a hammer
d) super b'stard tight - hammer plus loctite
Always gone for option b in the past and never had problems, but now I'm paranoid.
cheers!
'a' for me, refitted mine last week.
I'll let you know if/when it falls off.
loctite doesnt do it up any tighter, it stops it coming undone.
ive got the same issue, ive rounded a few pairs of cranks by not keeping an eye on them, and i think thats the key, do them "tight" by hand (a hammer is not a torque wrench old bean;)), so thats option A, with loctite to stop it coming loose, and then keeping an eye on it every month or so.
it only takes a second...
put copperslip in the hole then do it up very tight indeed.
I was quoted 50Nm, which is basically stand on a 110mm x 8mm allen key - but no hammering
copper slip lubricates it in, so you can do it up tighter, but also it comes undone easier as it remains lubricated.
Copper slip the taper itself, to allow the taper to slip on with low resistant, but be careful not to get it in the thread hole.
loctite the thread, which will lubricate it on the way in, and when it dries, help stop it working loose
.....IMO
what Olly said. I just had to bin a middleburn crankarm for the lack of some copperslip
then do it up very tight indeed
NOoooooo
Try to borrow a torque wrench and get a feel for just how NOT tight they need to be. Threadlock on threads helps them undo.
The cranks are soft and will deformed if over-torqued, then the bolt will not actually push down the crank onto the taper, and it gets deformed when you pedal.
45Nm and DON'T grease the tapers.
Greasing tapers is a myth that has done the rounds on forums for ages yet still people don't get it.
I was quoted 50Nm, which is basically stand on a 110mm x 8mm allen key - but no hammering
Does that not depend who's doing the standing? 🙂
Sounds like somewhere between a and b - its weird, I've never had this problem before, on plenty of square taper BBs, and I'm wondering now if overtightening has been the cause.
What I'd do is do them up pretty tight (upper body weight on heel of hand, medium bouncing) then stand on the pedals, first with one foot forward, bounce a bit, if there's any creaking, do them up a bit more, then stand on the pedals with the other foot forward, if there's any creaking, do them up a bit more.
I used to have problems with them coming loose, and did a few different things, until I started doing this ^ which seemed to do the trick.
...and DON'T grease the tapers
Oops 😳
... and always check tightness after a short ride following fitting
Greasing tapers is a myth that has done the rounds on forums for ages yet still people don't get it.
I'd say NOT greasing tapers is the myth. I occasionally work with dry assemby; but it is always for reasons other than mechanical efficacy eg in medical or aerospace where lubrication will cause other problems.
I go to 50nm wich is about as tight as you can go by hand with a normal 8mm allen key. Always use a bit of thread lock as well. If a crank has ever come loose slap some of this on the b/b taper.
http://shop.marksman-ind.com/loctite-641-bearing-fit-10ml-1734-p.asp
IMO grease the tapers an do up as tight as you can with an allen key by hand.
sheldon brown on installing taper cranks
http://sheldonbrown.com/brandt/installing-cranks.html
Greasing tapers is a myth that has done the rounds on forums for ages yet still people don't get it.
Indeed - and you would appear to be one of them!
The cranks are soft and will deformed if over-torqued, then the bolt will not actually push down the crank onto the taper, and it gets deformed when you pedal.
Another myth - you're likely to shear the bolt before deforming the crank.
Another myth - you're likely to shear the bolt before deforming the crank.
I have seen this, I even have some photos somewhere, with the nominally square hole partially rounded off 🙁
I don't doubt you - but that was surely due to repeated tightening when the crank bolt "loosened" rather than a single tightening.
From here...
[url= http://www.parktool.com/repair/readhowto.asp?id=103 ]http://www.parktool.com/repair/readhowto.asp?id=103[/url]
[i]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.
a. Wipe both sides of spindle and inside crank mounting holes with a rag.
b. Grease under head and threads of both bolts or nuts.[/i]
That'll do me 🙂
It's an interference fit so why would you want to grease the taper? If you remove the bolts the cranks don't fall off...
Got to do this soon - so did we decide 45 - 50 Nm?
Ta!
The other thing to watch for is taper match. There are two varients around: ISO and JIS.
ISO cranks should be used with ISO tapered BB's and so on... If they are mixed, the non drive side crank arm can work loose, fretting the hole in the crank arm which will make the situation worse and eventualy make the arm unusable.
One of the odd pairings is worse than the other. Helpfully I can't recall which but Google is your friend.
I found this out when using a FAG BB with a Stronglite chainset on an old tourer (JIS BB + ISO Chainset).
Hmmm, that old chestnut of whether to copper slip or not a square taper.
20 years ago bike shops would always have recommended that you don't lubricate bb spindles, then Shimano developed the cartridge bb. In the olden days if a bike was ridden regularly then every 3-6months you would have to take the cranks off to re-grease or tighten your bb. As the cranks were never on the bb for more than 6 months corrosion of the crank/bb interface was never that much of an issue.
Then when Shimano brought out their cartridge bb's, cranks seizing on axles became more of an issue. Shimano bb's can last for years and years. So if you have a crank which was installed dry and has not been moved for over two years then it dosent take a genius to work out that corrosion between the crank and the axle is more likely to happen.
So I think the correct is answer is that there is no correct answer. In an ideal world an interference fit will work better with two clean contact surfaces. But most bike shops will smear a very thin layer of copper-slip onto a bb before fitting the cranks, then they will apply thread-lock to the bolts. Therefore if the cranks aren't removed for ages there's less chance they would have seized on the axle.
I was always told that you need to the amount of grease that is on a typical mechnics fingers. i.e. a very very thin smear and no more.
Middleburn specify 28-32 ftlbs for their square taper crank bolts
OP - see if you can borrow a torque wrench to get a feel of how tight that torque is. If you mess up your crank arm or crank it will cost you more than a torque wrench
As for greasing or not greasing. Shimano supply their BB's with grease on the tapers, Phil Wood specify using grease (thin smear of course) to facilitate fit on their square BB's.
Phil Wood's BB installation instructions say:
"Clean and lightly oil the ends of the spindle, the square holes in the crankarms, and the crankarm mounting bolts. Install the crankarms securely on the spindle."
However:
One theory...
The taper on a BB spindle and crank is a press fit mechanism. The friction between the crank arm and the spindle causes the arm to slide on so far for a given amount of torque on the crank bolt. If you grease the spindle, the crank arm can slide farther onto the spindle, farther than it was designed to. The result is that the taper on the spindle forces the taper on the crank to expand. Multiple installations like this will cause the crank to move closer and closer to the BB shell, altering chainline and eventually ruining the crank when you pull the spindle all the way through the arm. BMXman
My take might be something like
steel spindle + alloy arm = no grease
steel spindle + steel arm = grease
titanium spindle + any arm = anti-seize
One theory...The taper on a BB spindle and crank is a press fit mechanism. The friction between the crank arm and the spindle causes the arm to slide on so far for a given amount of torque on the crank bolt. If you grease the spindle, the crank arm can slide farther onto the spindle, farther than it was designed to. The result is that the taper on the spindle forces the taper on the crank to expand. Multiple installations like this will cause the crank to move closer and closer to the BB shell, altering chainline and eventually ruining the crank when you pull the spindle all the way through the arm. BMXman
One theory which goes against all other engineering theory. The thing is if you don't grease the taper then you don't have a consistent fit for the same torque in the bolt - it will have a huge variation due to the difference in friction between the surfaces. Why put up with that sort of variation (which would lead to some being too loose, some too tight - assuming you consider too tight an issue) for the same bolt torque when you can just specify the torque for a greased fit - as indeed they do!
You also seem to have a plastic deformation due to tightening the crank onto the crank arm - something which just isn't going to happen given the forces involved.
As I mentioned above, a lot of the myths about crank installation seem to have arisen from people continually tightening the crank bolt when it "loosens" - where what actually happens is the crank squirms up the taper to equalize the forces (something it will do a lot less if you grease the taper!) This results in a decreased torque to tighten the crank bolt despite the bolt not having moved at all on it's threads. If you keep tightening in this situation you can do damage. Anyway this theory from BMXMan seems to incorporate a bit of that with it's "Multiple installations like this" comment.
As for the crank bolts, I always use anti-seize.
Here's what Middleburn supply with their self-extracting crankbolts (steel and Ti, although they have stopped making ti now due to the big cost increase)
"Apply anti-seize compound to the thread of the bolt...Apply Loctite 222 locking compound (purple) to the threads of the Self-Extract cap...check the tightness of ...bolts after first ride and periodically afterwards"
thread lock on threads helps them undo.
errrr.
say WHAT!!!?
greasing surfaces stops creaking, thefore its a good thing.
Its the gospel according to Joe/Olly:
If in doubt, grease it!
Greasing tapers is a myth that has done the rounds on forums for ages yet still people don't get it.Indeed - and you would appear to be one of them!
The cranks are soft and will deformed if over-torqued, then the bolt will not actually push down the crank onto the taper, and it gets deformed when you pedal.
Another myth - you're likely to shear the bolt before deforming the crank.
I have seen sqare taper XTs pulled right down so that they wobble with the bolt done up tight; otherwise good cranks going in the bin due to overtightening.
smiffy - read my link above to sheldon brown that explains why this happens - its not overtightening with a greased taper that causes it.
TJ, why refer to an article that contradicts your position?
smiffy - reread it.
"The claim that a greased spindle will enlarge the bore of a crank and ultimately reduce chainwheel clearance is also specious, because the crank cannot operate in a plastic stress level that would soon split the crank in use. However, increased engagement depth (hole enlargement) may occur without lubricant, because installation friction could ream the hole."
"Lubricating the spindle for assembly assures a predictable press fit for a given torque."
wibble. i've read the op properly now.
I have always greased, even with cotter pins. Never had a loose crank, never had a deformed crank, never had a crank that could not be removed.
Me too epicyclo. Many years of crank fitting with no issues
I never make a metal to metal interface of any sort dry. always grease, loctite or antiseize as appropriate.