tiger1964 

I love how smooth the new Velo Orange sealed bottom bracket is. Finally riding again, the past week or so, recovered from February's crash.

I decided to recheck the crank-to-spindle mounting bolts after a ride or two. Yup, needed a further tightening. Then again after the next ride. And the next (my usual local ride is 18 miles). So, after 7-10 rides, needs it every time, and I suspect again today. Now, it's no more than 1/8th turn or even less each time. This is new to me, never had such a problem before.

So, either (a) I have a spindle-taper issues, somewhere I could possibly look up what taper 1980 Avocet cranks have or (b) the bolts (using the ones supplied with the bottom bracket) are backing out. I am tempted to do something I do not recall ever needed to do on any crankset -- put threadlocker on those bolts. Hmm, that would help if it's (b) but if it's (a) it's going to be hard to diagnose once the thread locker is on. Perhaps there is a (c) that has not yet occurred to me.

Any contraindications here?

wschruba

Yes, tapered power-transfer designs behave funny. Remove the cranks, reinstall them with a slight wipe of oil on the tapers, and tighten to 30ish foot pounds (40ish NM). Ride for a few miles, re-tighten, and then leave them alone. You certainly may use loctite the second time you re-tighten, but if they work loose (creaking or knocking), the taper is already shot, and the cranks are NG. This assumes you know the history of the crank, and that the tapers that you have used with it match.

bwilli88 

Put some beeswax on the threads and it acts a bit like loctite but easier to remove.

tiger1964 

Will do, have a torque wrench handy.

No idea on the Avocet cranks, because (a) info on Avocet stuff isn't as ubiquitous as some other brands, and (b) I have not looked. As for knowing the history, I suspect when I bought the bike on eBay in 1998 the cranks had never been off. I have twice, once in 2017 when I started riding again, and again over the winter to install the VO bottom bracket.

Interesting. Alas, I have Loctite here, but not beeswax so, this time...

rhm

I have recently had this problem with two different cranks, both older cranks that were new to me. The tapers look fine. I should say they looked fine before I installed. Both cranks worked loose on the first long ride, and I had to tighten them occasionally just as Larry mentioned.

Please don't tell me the taper is shot. These are older cranks, no longer made, and I mean to make them work as long as I can. In both cases, repeated tightening seems to have done the trick for now, but I am prepared to tighten them again if that's what it takes.

Nonetheless, and this is not a rhetorical question: what can possibly go wrong? Seems to me the possibilities are (1) no amount of tightening fixes the problem (either the crank arm eventually bottoms out and can't be tightened anymore, or the crank splits apart at the tapers or (2) we reach a point where the crank arm is permanently pressed onto the spindle and cannot be removed again without serious damage. What else?

jimmuller 

On the question of Loctite, I would not think the bolt is coming unscrewed. I sure wouldn't put Loctite on the taper itself!

daviddavieboy

I have never tried but I wonder if a film of JB Weld was used and allowed to COMPLETELY dry would work?

trailangel

Stop retighten the cranks or you will ruin them.
The bolts are not loosening, the crank arms are working their way further up the spindle.
If you tried to pull the cranks off you will find they are on really tight.
https://www.renehersecycles.com/wp-c...2016_03web.pdf

tiger1964 

I wonder what brand/model cranks? Perhaps some are prone, some others immune?

Yeah, I meant on the threads.

I am beginning to suspect THIS. Gonna Loctite (capitalized as otherwise the spellchecker keeps trying to change it to "lactate", not going to try that on my cranks ) the bolts and hope for the best. If the crank arms deteriorate, I might be shopping for some Campy cranks as most of the rest of the bike is Campy. I happen to have an extra set of Stronglight 93's... but on an Italian bike???

Perhaps Avocet cranks are just soft? NEVER had this before on any cranks -- my own, friends' or the 100's I worked on in my bike-shop days; not even Maxy cranks which I always presumed where made of alumibutter.

Plus I should also check w/VO on the taper type on their bottom brackets.

clubman 

Cranks were ridden loose and started to distort?

non-fixie 

I have never re-tightened cranks.

Sometimes, when removing, I find the bolts need surprisingly little force.

I have also never experienced any play in my cranks.

FWIW.

Salamandrine 

I used Avocet cranks for 2 or 3 years BITD. They are rebadged Ofmega CX cranks. While they were nominally campy interchangeable, IIRC, the tapers are somewhat on the small side. Sheldon Brown mentions this somewhere, but exaggerates (IMHO). ISO and JIS spindle standards didn't really exist then, I'd still guess they'd be a much better fit on an ISO BB. I think I used one with an Avocet BB for a time, then moved it to a Zeus, which also have a smallish taper. Both worked no problem.

How far does the end of the spindle extend into the crankarms now, with the bolt taken off?

I don't know what alloy they used but it wasn't soft. Presumably 6061.

Sometimes I'll snug up a crank after the first ride just to check, once. If a crank has to be tightened repeatedly, something is seriously wrong. If cranks have been ridden loose for a while, it generally ruins them.

Aubergine 

SurferRosa

Sheldon taught me to mount the cranks, ride the bike around the block a few times, retighten, and don't touch 'em again.

non-fixie 

That sounds like a wise idea. Did they ever need that, in your experience?

Thinking about it, since riding around the block is something I generally do several times during a build, as well as checking the most important bolts (stem / seatpost / cranks / chainrings) before considering it done, I may actually have followed Sheldon's advice more often than not.

SurferRosa

Well, they always tighten a little more. So ... I guess.?.

BoozyMcliverRot

I have found that the 8mm Allen bolt type crank bolt is prone to stretching. You could use the type with a hex bolt and use a socket to tighten it. In my experience they will hold better.

79pmooney

Tapered cranks rock slightly as you pedal. In that rocking, they slide slightly inboard. This means that a properly torqued bolt can always be tightened further after you have ridden. Do this and the crank slips further onto the spindle.

Now think about what is happening to your crank as you do this. Every time you re-tighten and ride again, you drive the wedge of the spindle a little further into the tapered hole in the crank. What happens when you drive a wedge into something far enough? That something breaks. Mankind had been using wedges to create cracks and splits for many thousands of years. With a hard enough wedge and enough movement of that wedge, the part always breaks.

Listen to Sheldon. Ride once around the block, re-tighten - and stop there!

Ben

tiger1964 

Huh?

What came with the BB is 14MM hex bolt. Not the world's biggest mating surface on the flange under the head of the bolt, maybe needs a washer to spread the "load" over more of the face of the hole in the crank (hard to describe).

Interesting question. I just took off the RH bolt, looked inside; more space in there than I suspected. The crank arm would have to move inboard 7mm-8mm before the spindle end was flush with the crank arm's bolt-mounting surface.

Another data point - on yesterday's ride, for the 1st time in a while, I had an overshift where going to the outer chainring the chain went off the outside of the outer chainring. Coincidence? Or not? Maybe the crank arm is slowly moving inboard.

The Golden Boy 

This.

I've been using an Avocet BB and spindle with mine.


1986 Trek 400 Elance by Dave The Golden Boy, on Flickr

bulgie 

Sounds like you doubt it, but it's true. Due to friction while mounting, the crank is under strain, and when it squirms around from riding, it slides further up the taper on the spindle to relieve that strain. After a while the forces are in equilibrium, and the bolt will seem looser if you wrench on it.

I recommend using crank "dust caps" which are really locknuts for the spindle bolts. The spindle bolt will not loose (as in backing out) if there's a dustcap cinched down on it. I don't always follow that advice myself -- my bikes have often not had dustcaps. But they didn't loosen either. If I had a bike where I suspected the bolts were backing off, I would definitely slap some dustcaps on that bad boy.

Yes you absolutely must have a washer under the bolt head. Some bolts have the washer built in, in which case maybe you don't need a separate washer.

8mm is too much, indicating the wrong spindle taper -- it's too big. A smaller taper will poke through further, giving you more area in contact between spindle and crank.. Too small of course would have it poke all the way through until it hits the washer under the bolt head -- no good, because it can't tighten any further after that point.

Some people think there's just ISO and JIS standards, but those Avocet cranks were made before those standards even existed. BITD, almost every crank maker had their own idiosyncratic taper spec, sometimes interchangeable with some other brands, sometimes not. I don't know what spindle you need, but ISTR Avocet was one of the weirder ones. It may be that the spindle you need is an Avocet and nothing else works (I don't know, but it's possible).

You might want to ask Greg Reiche (pronounced "Rich") of Cycles Hibou, he's the most knowledgeable guy I know about historical spindle tapers and compatibility.

There was a very interesting thread on internet-bob mailing list last year titled "BB taper standards and false binaries". The "false binary" is the ISO/JIS one -- the idea that there are only two taper standards is false.

Mark Bulgier
Seattle

merziac

On the 1 or 2 that have done this for me, I apply "diminishing returns" if the bolt is not tight but the crank arm seems to be I just snug the bolt down, not fully retorque and monitor to see. If the crank arm stays tight then you could locktite the bolt and call it good while still keeping an eye on it.

Also fully agree with Mark on the dust caps, one of their many functions are as a failsafe locknut, they also protect the threads so the puller installs properly to remove the cranks.

Kuromori

I think it helps to point out the forces at play.

There's the taper (wedge) which wants to push the crank arm outboard. There's the bolt (screw) which wants to pull the crank inboard. Finally there's friction, which is quite high, which wants to resist movement in either direction (crank won't come off without a crank puller).

When you initially tighten the bolt, it works against the taper and friction. Since the initial state is outboard since you are moving the crank inboard with the bolt, friction will resist inboard movement, meaning the crank will be outboard relative to where it would be without friction. (think sticky cables)

Cranking motion imparts loads on the crank that allow it overcome friction and shift slightly, but without tightening the bolt. There will be a tendency for the crank to move inboard since the force initially provided by the crank bolt is equivalent to the force of the taper plus friction. Eventually the crank creeps towards where it would be without friction, which is inboard of the initial tightening.

This means the bolt gets "looser" because what it was pulling against moved, but without unscrewing. At this point, tightening the bolt will preload it and pull the crank inboard more causing it to creep further inwards when it again moves to where it would be without friction. Conversely if you remove the bolt, pedaling action will overcome friction and allow the crank to creep outwards since the taper pushes the crank outboard but there is no bolt to push it inboard. This is also why you're not supposed to tighten crank bolts on cranks already installed. Crank bolt torque is higher than what is is supposed to end up at.

Salamandrine 

8mm is way too much. The problem is that the BB has the wrong tapers. As I said previously, I suspect an ISO BB will work pretty well. ISO is just a touch smaller than vintage Campy record, as was Avocet.

HTupolev

When you pedal, you put strong forces on the square taper interface: you're basically rocking the crank arm around on the spindle. If the crank bolt wasn't in place, the crank arm would gradually squirm outboard until it falls off of the spindle.

When you first installed the crank arm, the crank bolt was pressed VERY TIGHT against the arm, since it was just used to push the arm up onto the taper. But as you cause the arm to squirm on the spindle under your pedaling forces, it budges against the crank bolt, causing it to ride inboard up the taper. It will keep moving inboard until its contact with the bolt is soft enough that squirming doesn't budge it inboard anymore. This process happens every time you re-install a crank arm onto a spindle, and every time you re-tighten a crank bolt. It permanently widens the taper on the crank arm, and after enough cycles this will destroy the crank arm.
Because the crank arm crawls away from the bolt, the bolt feels like it's tightened less strongly against the arm, even though the bolt didn't actually back off.

You can check whether the bolt is actually loosening by drawing a line on the head so that you can see if it has rotated since you last looked at it.