Loose Crank Arm Problem

I've no idea, I'm not a mechanic. One on here said "don't grease".

However, I'm pretty sure that "grease"/"don't grease" could be a situation when you need to call in the Internet UN peacekeeping force.

However, I'm pretty sure that "grease"/"don't grease" could be a situation when you need to call in the Internet UN peacekeeping force.

I was thinking more social services

This thread has made me paranoid! Looking for some advice.

I want to replace my bottom bracket and reinstall the cranks. I have the Park Tools crank remover, BBT-32 tool, large adjustable wrench and the long Park Tools 8mm hex key.

Is it possible to apply 40Nm of torque using the long 8mm hex key to re-secure the cranks properly? I'll be honest I don't have a 'feel' for torque yet, I'm very new to repairing bicycles. My gut feeling says no, as the hex key is only 16cm long, so that would be the equivalent of hanging a 60kg-ish weight off the end of it to get it up to spec.

I have a small torque wrench already that does 2-24Nm. I'm open to buying a higher torque one, can clicker wrenches do right and left hand threads? Is there anyone in the SE (Brixton, Herne Hill) area that might lend me/let me use one under close supervision one for a few beers?

Cheers!

You can put that much torque into a small tool like that. The longer the tool the more accurate the measurement will be.

I think if you use your 24Nm mini wrench and then use your better judgement in how much beyond its limit click you need to go to achieve 40Nm

I've always believed and practiced that you don't grease square taper but if there's any splines involved then grease it (lightly).

I find that metal -> metal doesn't always = creak but metal -> metal + some contamination, grit etc usually does = noise of some sort.

Grease FTW

Subject: Installing Cranks
From: Jobst Brandt
My cranks get loose, quite quickly too; over about 10 miles or so from being solid to flopping about in the breeze. Any suggestions?
One or both of the cranks are ruined!* Once ridden in the "floppy" mode, the tapered square bore of the crank has been deformed and can no longer be secured on a spindle. Install and properly tighten new cranks on the spindle after greasing the tapered square ends of the spindle. Proper tightness should be achieved with a torque wrench or by a skilled hand.
The admonition not to grease the spindle finds life mainly in the bicycle trade. When I discussed the "dry assembly" rule with crank manufacturers, I discovered that they had warranty claims from customers who split cranks. However, cranks cannot be split by overtightening them. This can be proven by attemting to do so. An M8x1 bolt is not strong enough to split a major brand crank.

Failure from "over-tightening" is caused by repeated re-tightening of properly installed cranks. In use, an aluminum crank squirms on its taper and, because the retaining bolt prevents it from moving off the taper, it elbows itself away from the bolt and up the taper ever so slightly. The resulting loss of preload, after hard riding, can be detected by how easily the bolt can be turned.

Loss of crank bolt preload is greater on left than the right cranks, because left cranks transmit torque and bending simultaneously while right cranks transmit these forces separately. The left crank transmits driving torque through the spindle to the right crank and chainwheel while the right crank drives the chainwheel directly. Besides that, the right crank transmits torque to the spindle only when standing on both pedals. Doing this with the right foot forward (goofy footed) is the only time the spindle transmits reverse torque.

Mechanics, unaware of why crank bolts lose preload (and commensurate crank tightening), have re-tightened bolts until cranks split. No warnings against re-tightening properly installed cranks are evident although it is here where the warning should be directed rather than at lubrication.

Because friction plays no role in torque transmission, preload in the press fit must be great enough to prevent elastic separation between the crank and spindle under torque and bending. This means that no gap should open between crank and spindle facets under forceful pedaling. Crank bore failure occurs when the press fit is loose enough that a gap opens between spindle and crank. Torque is transmitted by both leading and trailing half of each facet, contact pressure increasing and decreasing respectively. In the event of lift-off, the entire force bears only on the leading edge of facets and causes plastic deformation, causing the bore takes on a "pin cushion" shape (loose crank syndrome). Subsequent tightening of the retaining screw cannot correct this because neither the retaining bolt nor crank are strong enough to re-establish the square bore.

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.

With or without lubricant, in use, cranks will make metal-to-metal contact with the spindle, causing fretting erosion of the steel spindle for all but the lightest riders. Lubricating the spindle for assembly assures a predictable press fit for a given torque. Without lubrication the press is unknown and galling (aluminum transfer to the steel spindle) may occur during assembly. After substantial use, spindle facets may show rouge and erosion from aluminum oxide from the crank, showing that lubricant was displaced.

Crank "dust caps" have the additional duty to retain loose crank bolts. Because crank bolts lose preload in use, they can become loose enough to subsequently unscrew and fall out if there is no cap. If this occurs, loss of the screw will not be noticed until the crank comes off, after the screw is gone.

Jobst Brandt

This thread has made me paranoid! Looking for some advice.

I want to replace my bottom bracket and reinstall the cranks. I have the Park Tools crank remover, BBT-32 tool, large adjustable wrench and the long Park Tools 8mm hex key.

Is it possible to apply 40Nm of torque using the long 8mm hex key to re-secure the cranks properly? I'll be honest I don't have a 'feel' for torque yet, I'm very new to repairing bicycles. My gut feeling says no, as the hex key is only 16cm long, so that would be the equivalent of hanging a 60kg-ish weight off the end of it to get it up to spec.

Almost certain it will be possible, the long Park hex wrench is the de rigeur tool for tightening and loosening crank bolts. I'd be very surprised if anyone made cranks that couldn't be tightened with that.

That said, I have never, while spannering personally or professionally, used a torque wrench on crank bolts.

Unless you are Mr Universe or unbelievably weedy then just make them as tight as you can and they'll be fine.

If you want to worry about torque values then I'd be more worried about what it'll take to shift your bottom bracket out of the frame, that's generally what seizes and requires silly amounts of leverage (tool in vice and use frame as a lever) to move.

Don't tighten as much as you can, that's just stupid advice on something that's taper fit. As mentioned earlier in the thread, you will feel the crank meet the spindle. From there tighten it, don't heave it tight as that'll ruin it.

IMO grease should be used on the taper. As with bolts, a greased bolt will stay in where an un-greased bolt will be more likely to work it's way loose.

Well I'v never had any problems on any of my bikes nor my customers bikes.

Maybe "as tight as you can" isn't quite right though. I wouldn't say you'd want to be going blue in the face with the effort you're putting in to tighten them or be moving your stance so you can force them tighter but I think I generally horse them up till they don't go any tighter as opposed to the likes of a stem bolt which is much more about "feeling" how tight the bolt is than tightening till you can't go any further.

don't go doing what I did once upon a time on the way to work
http://fixedgearwales.blogspot.com/2009/07/dopey-sion-oh-dear-oh-dear.html

I have a bike that has this problem, The crank is still square, and the much harder spindle looks fine too. It's a strange chainless bike with a drive shaft, but I think you may want to replace/upgrade the crank bolt (sometimes they dont fit snug - it should also be the allen key type if pos.) and then torque about 10% more than specified.

Grease the inner flange of that crank bolt.

Also, it's always the non drive side that comes loose as the drive side does not carry much or any real torsional load on the axle. Left side transmits power through the spidle and puts a lot more stress on the Square taper.

Thanks for the advice every one, very helpful.

I'm reasonably satisfied that I've done it right reading the descriptions here, the bolt pushes the crank onto the spline creating an interference fit, and when it reaches the correct point on the taper the force required to move it on becomes huge. At this point I did them up moderately tight by applying as much force as I can without doing anything stupid like standing on the allen key.

My gut feeling is that you would have to be gorilla to over tighten with the Park Tool 8mm hex key.

alley key you say... my torque wrench is 2 feet long and i still lean on it. I wonder how tight it really is?

Reminds me of a hill in Wales we tried to bike up, it got so steep we had to get off and push -- and then that became difficult. Everyone has a different idea of a steep hill I guess. loose means something, hand tight also, but when it comes to tight, very tight,.. etc. it gets a littly airy. If you're around FInchley, or West Hampsted I'll torque it for you if you like. What Cranks are you using?

Tumbleweed, this is exactly why I love a torque wrench.

As mechanics go I'm not very strong. I know that I am not a great judge of what is tight enough, so having something like a torque wrench is essential.
I personally feel like if you are trying to work to a certain standard without one, you will be disapointed.

They are pretty cheap and nasty FSA Vero single speed cranks that came with my OTP fixie I use for getting to and from work.

I think I might just get a bigger torque wrench, saves all this wondering.

OK, well I splashed out on a torque wrench, gut feeling is that I wasn't reaching 35-45Nm required to push a crank onto the spindle, as it required a bit of effort!

Constantly had an issue with this on some old cranks with a bit of a bent taper, so the bolt was constantly being undone by the microflexing every turn. I just put a smidge of araldite on the inside thread of the bolt, then tightened it up loads. It was totally undoable, though don't do this unless the crank and bb are sufficiently beaterish.

I've been having a very similar problem on a Sugino RD2 crankset. Tapers appear fine. Only using an Allen key to tighten, which may be the problem. Can anyone who knows about such things say why it's a bad idea to use threadlocking compound (Loctite 243) on crank bolts?

I've been having a very similar problem on a Sugino RD2 crankset. Tapers appear fine. Only using an Allen key to tighten, which may be the problem. Can anyone who knows about such things say why it's a bad idea to use threadlocking compound (Loctite 243) on crank bolts?

It's not the taper that is the problem, it's the arm itself - the profile of the section that sits on the BB taper won't be square any more, and you will need to replace the arm.

Are you using tiny multitool Allen keys? I had a similar problem, you cant tighten them properly as you just cant get enough torque with a diddy allen key, buy yourself a proper one and grease the bolts and it should stay where it is.

I saw a guy this morning at the side of the road who had snapped his crank arm in half...shocking start to the day. Pedal clean off under the shoe!

Happened to me about 30 mins ago coming onto southside of Waterloo Bridge. ouch. Any way to pre-empt? I suspect not, but thought I'd ask.

Not really, It can spread from the tiniest of crack or simply fail due to poor casting. You could keep them clean and checking every couple of weeks, but it's not exactly a common thing to happen so it may end up a waste of time

You could keep them clean and checking every couple of weeks

So not gonna happen :) Cheers for the advice though. To be fair, twice in 15 years isn't bad going. The 1st time was clearly shoddy workmanship. I think this one was a crack, from the discolouration of about a 3rd of the metal.

This just happened to me the day before the Herne Bay ride, while doing serious speed downhill. Scared the living shit out of me.

/Still coasted down the hill like a boss though..

FSA Gossamer. Anyone had good/bad experience of them?