Square taper crank fitting queries

[Tim Hall]

Compromise: Put grease on only two faces of the taper. 

[Crumbling Nick]

Can someone explain the reason for using threadlock? All the crankbolts (only Shimano & Sakae) I have used have a means of preventing the bolt unscrewing when the clamping load has relieved itself  . I don't like the deep serrations on the clamping face of the cheaper bolts, since they cut their way through the crank every time they are tightened, but I have seen no evidence that they don't work.

Do Campag bolts lack an equivalent? It would surprise me.

[Sergeant Pluck]

Does enough tension remain in the bolt to keep it there after the cranks move along the taper?

Re the threadlock - I'm thinking of going with Campag's manual on this one, and they state no grease on the bolt or washer. On the other hand I am reluctant to put the bolts in dry in case of corrosion (although they do appear to be treated in some way).

The Campag bolts and washers for the Record Pista cranks do not have any serrations.

[Crumbling Nick]

The better quality Shimano bolts have a large captive washer with a rubbery part that presses against the crank (extraction) threads to stop it rattling out, hopefully without letting the bolt unwind (smiley for crossed fingers).

[Biggsy]

Bolts on Campag square-taper cranks can theoretically unscrew themselves and fall out as there's nothing to retain them apart from thread tension.  That would be extraordinary, though.  For my sins, I use alloy bolts with one Campag crankset - which can't be tightened as much as steel bolts - yet even these I don't need to threadlock.

Does enough tension remain in the bolt to keep it there after the cranks move along the taper?

Yes, in my experience.  It might be different if the cranks aren't fitted tight initially and the rider is very powerful (which may cause more squirming).

[Steve Kish]

For my sins, I use alloy bolts with one Campag crankset - which can't be tightened as much as steel bolts

I still have a pair of these somewhere (Sugino, IIRC) and was told that you should tighten the crank with a steel bolt and then remove that and replace with the alloy one, just nipping these up, as any force on these will just strip the thread.

[Biggsy]

For my sins, I use alloy bolts with one Campag crankset - which can't be tightened as much as steel bolts

I still have a pair of these somewhere (Sugino, IIRC) and was told that you should tighten the crank with a steel bolt and then remove that and replace with the alloy one, just nipping these up, as any force on these will just strip the thread.

Yes indeed, it's essential.  My SRP ones can be tightened enough to stay put even without threadlocker, but you certainly couldn't push the cranks on properly with them.

[Crumbling Nick]

Does enough tension remain in the bolt to keep it there after the cranks move along the taper?

I suspect that the answer may be "not always". I have a vague memory of the odd story of a bolt falling out, probably on rbt. A quick Google search of rbt reveals the inveitable collection of bun fights as well as some poor quality evidence that it happens as a result of bad practice in competitors' (maybe... but rbt is rather American) workshops. Realistically, it would take a lot of time & effort to understand the risks.

The Sakae bolts of my experience dated from 1980. Presumably the question is older than that.

Meanwhile, Biggsy's advice to use threadlock looks eminently pragmatic for Campag bolts. A pertinent quote from Andrew Muzi on rbt may help - "p.s. most modern cranks now use a thread lock compound (the blue stuff
on the bolts). "

[Gattopardo]

I have no idea about all this.  I just tighten the bolts or nut up.  If they are lose I just tighten them up.

Am I doing something wrong?

[Biggsy]

I have no idea about all this.  I just tighten the bolts or nut up.  If they are lose I just tighten them up.

Am I doing something wrong?

Possibly, if they're not tight enough in the first place.  A crank coming loose is a pain and can damage the crank.  With the square taper design, you're not just tightening a bolt/nut, you're also wedging the crank on the spindle, so it can take more force to do it reliably than some think.

Also it's not a good idea to keep on retightening - for the reason described in the Brandt article.

[mattc]

So if your bolt comes loose - and you believe you torqued it correctly - what is the Best Practice next step?

[Sergeant Pluck]

It's never happened to mine, past or present, but my reading of all the above is that best practice would be to remove and refit the crank.

[Biggsy]

I would just refit the bolts with threadlock unless I suspected something wrong with the cranks.

It may generally be bad practice to retighten the bolts, but that doesn't mean you can't do it when the bolts themselves have turned rater than becoming effectively looser from crank movement.

[Sergeant Pluck]

In the end I went for dry on the tapers + threadlock on the bolts. All went fine, although I was surprised at how many turns I was able to put in before the torque really started to ramp up past 30 Nm or so.

Also, it was clear that if I'd put some welly into it, as indeed I would have done in the absence of a torque wrench, I could have pushed the cranks further on. But the majority of the taper is engaged and I forced myself to stop at the specified max.

[Sergeant Pluck]

Having said all that, the cranks are not on equally on both sides. Should this bother me?

[Biggsy]

Having said all that, the cranks are not on equally on both sides. Should this bother me?

Not if they are on tightly enough and you're happy with the chainline and Q.

[Sergeant Pluck]

Thanks Biggsy. There's not much in it. I guess it ties in well with J Brandt's comments re consistency of press fit in the absence of grease.

Tight enough? Certainly tightened up to specified torque. Chainline good.

[Chris N]

The tolerance allowance* in the ISO standard for crank tapers means that there could be as much as 2mm axial difference between the final crank positions, so I'd expect some variation from side to side.

Apparently (I don't have a copy of the standard itself, but it is stated in my copy of Sutherland's) there is no similar tolerance in the equivalent JIS standard.  The taper angle is the same, but the distance across the flats is 12.65 - I presume this is measured at the very end of the axle.

* Included taper angle: 4° ±10'
Dimensions across flats, 1.5mm from end: 12.6 +0.02/-0.05 mm

[Sergeant Pluck]

Looks like about 1.5 mm difference. Thanks chris n.

BTW are you a greaser?

Changed my mind  Removed cranks, cleaned it all down, started from scratch. And greased the tapers.

I feel better now.

[Chris N]

BTW are you a greaser?

Hell no. 

Well, just the screw threads and under the washer/head of the screw. Never the tapers.

[Sergeant Pluck]

Hell no.

Off they come again, then 

I jest.

[rogerzilla]

The operative at the Ridgeback factory many years ago did not grease the tapers when fitting this crank.  After a couple of decades sitting around in a damp atmosphere, the crank and BB can get very, very stuck.  The extractor tried its best but then ripped out all the threads.  So more drastic means became necessary.

2021-09-12_08-22-17 by rogerzilla, on Flickr

Grease your tapers.

[mzjo]

The operative at the Ridgeback factory many years ago did not grease the tapers when fitting this crank.  After a couple of decades sitting around in a damp atmosphere, the crank and BB can get very, very stuck.  The extractor tried its best but then ripped out all the threads.  So more drastic means became necessary.

2021-09-12_08-22-17 by rogerzilla, on Flickr

Grease your tapers.

I would have been inclined to warm that one up first. My order of things would be extractor on and well under tension, start warming (hot air paint stripper probably, keep the blowlamp for steel!), wind on a bit more tension and eventually it should might come off with a bit of a bang. I did this once with a well stuck MZ clutch basket (which has a round taper) and oxy-acetylene. It didn't half go bang when it came. Really lept across the workshop! Aluminium, expanding rather more than steel, should come away a bit easier (and if you lose patience you can always melt the bugger to DETH!!!! °

[aidan.f]

Some advice for our OP. I had a new square taper crankset running out of true and rubbing the front mech cage. Rotating 1/4 turn cured the problem. I also dismantled the chainset and  de-burred the big ring fixing holes which may also have helped.