Crank torque question
 

Let’s say you install a set of cranks on a square tapered spindle with a torque wrench, both sides to the exact same amount, and the result is the DS arm sitting further out from the seat stays as the NDS arm. What is the cause of this?

Also what is the fix? Just leave it?
Should I tighten the DS until both sides match? I have room on the spindle and clearance with the inner ring, and the chain line does look a little too far out to me.

Much thanks in advance for any ideas or thoughts or help you can give me, you guys never steer me wrong!

-Erin

Do NOT mess with the proper torque.
I'd venture to guess, if you looked at dozen bicycles, you'd see they aren't all symmetric.
This is an old spindle chart and you can see not all spindles are equal.


https://cimg5.ibsrv.net/gimg/bikefor...f0dc3a3923.jpg

hmmm interesting. I see your point on the asymmetry, I suppose I can just add pedal washers if my pedal needs to be spaced further out on the NDS.

Would it change your mind at all if I told you the bottom bracket (spindle and NDS cup) and crankset in question was T.A. Specialites? I couldn’t really find agreement online as to the proper crank bolt torque for old TA cranksets. I did torque the crankset arms to 25Nm as per another post I read on here, maybe should I have gone higher?

Higher torque isn't going to change the position of the crank very much, but you may shear the fastener or strip its threads.

Just a minor FYI - the tubes I think you are referring to are CHAINstays.

Wider spacing on the driveside is very common. Very rarely have I ever encountered someone who notices the usual 5-6mm difference at the pedals.

IME check how far the inner chainring is to the chainstay, usually @3-4mm is sufficient. If there is a significant larger gap then check the chainline and maybe try a different bb axle ?

IIRC the torque spec for cotterless crank bolts has always been around 28-30 foot pounds, regardless of brand. I don't know the Metric type measurement. I'm so old they hadn't invented the Metric system yet in 'Merica.

"Overtorqueing" to correct spacing seems very wrong to me. You might have a compatibility issue with the TA cranks ?

Typical is about 30 lb-ft or about 40 Nn

Asymmetrical BBs were the standard when I started this stuff (that being 1973 for the first real taxable paycheck). Common delta, between the two sides, being a few mms to 6+mms. Depends on the number of chainrings. Andy.

Woah, well ok, guess I’ll tighten both to 40Nm tomorrow and see what that does, thanks everyone!

I don’t see how though, it’s a TA crank and a TA spindle and even a TA NDS cup.

the spindle may be an offset one that got installed backwards... happens frequently with old style non-sealed BB assembies.

Back when these cranks were OEM items the crank arm retaining bolt tightness torque levels were generally lower than these days. IIRC there was a concern about he arm's softness and tapered hole expansion due to overtightening (and drawing the arm further up the axle's taper, opening up the tapered hole in the arm). I recall about 25 foot pounds as being the suggested level.

Too much torque will ruin the arm and that would be a shame. As mentioned the design is meant to locate the arm, relative to the axle, at a point that keeps the arm on the axle due to the bolt's force, and no more (and if less the arm loosens up). Using this tapered fit as the adjustment for chainline is asking for damage. Generally there's only a few MMs of arm pull up onto the axle's taper to achieve the needed securement and this is from a completely loose arm to one that is properly torqued on. This is why various BB axle lengths and BB cup spacers are about, they do the job of placing chainline as it needs to be.

Last point I'll mention is that these days there's far more effort at standardizing bicycle dimensions and component interface specs. With so much cross boarder trade a bike is made in a number of countries these days, only the final assembly location is usually mentioned. For this many country sourcing to be effective each country (factory) has to make their part to the right spec. Back in after WW2 world the bicycle industry was still largely still independent from country to country and the dimensional specs one country followed weren't the same to the other countries production. During the 1970s the western world started to form internationally agreed on specs and the need for cross boarder compatibility grew. ETRTO is an example and ISO thread specs another.

One disadvantage to this was less than best function, or a function that was fairly "basic" and, with shifting as a good example, asked the rider to develop their technique to mitigate the mixed combination of components that could end up on a bike. While I have always had some resistance to the 500 pound gorilla that Shimano was (and their dictating frame specs needed to fit their components, SIS as example) I do give them a lot of credit to figuring out that they needed to control as many details as possible to have their products work better than their competitors (SunTour, Campy, Simplex, Huret). Being able to design tooth profiles to mate to specific chain shaping resulted in their drivetrains shifting far easier than what was available just a few years before, and was instrumental in the path to indexing for the sport riders.

I still run tapered square BBs and cranks because they work so well and offer so many set up options. Andy.

Pedal washers are only used to stop the pedal from chewing up the face of the crank when you screw it in. Using spacers on the pedal spindle will significantly increase the risk of thread damage as engagement is reduced. Don't worry about crank asymmetry, you probably don't sit straight on the bike anyway.

You risk stretching the crank if you overtighten it.

Well the cranks are on there nice and tight already with just 25nm so I’m just going to heed the warnings and leave them as is. And note taken, torque should not be used to adjust the chain line; I think that was a point I hadn’t quite grasped, although it seems kind of obvious now. I dialed in the Jubile derailleurs with this triple this evening and everything is now working like a charm, thanks everybody!

Why would he be risking anything by tightening them properly? 25 is too low.

https://www.parktool.com/en-us/blog/...s-and-concepts

This was pursuant to Andy's comment #11.

Andrew's suggestion was 25 ft. lbs. That equals 33.9 Nm, not 25.

There is a danger in being too low as well.

Too little torque can and will lead to the arms loosening and being ruined. It usually seems fine when the bike is in the stand, but the loosening up will happen when you are 10-30 miles away.

Campagnolo had a series of technical seminars when I was younger, around the time of the 84 Olympics. They recommended to run your greasy fingers over the end of the BB axle when mounting the arms. You don't need or want a lot of grease in there.
Grease the threads and under the head of the crank axle bolt in order to get a more accurate torque measurement. Torque it to 28-30 foot pounds and you should be set.
Make sure to re-check the front derailleur adjustment because if / when the crank moves inward the limit screws will allow the chain to overshift off the large chainring and then you'll scratch up your crankset

No torque wrench ? I kid you not, the old-timers used to say to tighten them up to "two grunts" tight. Pedals and threaded headsets were closer to 1 to 1.5 "grunts".

Things were not always better in the past . . .

It's not the loosening that causes irreparable damage so much as not noticing it, or noticing but trying to ride home anyway. Initial loosening may cause a little deformation in the crank taper but usually not so much that it prevents refitting and continued use. If in doubt carry the tools you need to tighten the crank bolt. Were old TA crank bolts the same M8×1.0 as modern cranks? I don't recall, but if so just carry a spare modern crank bolt and an 8 mm Allen key.

Hence why I wrote "overtighten". There's no mention of antique TA cranks in that list.

Campagnolo said that this will make the cranks plenty tight. Worked for me.


https://cimg5.ibsrv.net/gimg/bikefor...0e5482f14a.jpg

Soooooo do I tighten the crankarms up to 32 ft-lbs? Or no? It is a TA spindle and crankset but a newer set of bolts, I think sugino labeled bolts.

Different bolts do not matter at all. Some worry warts keep posting to use lower torque. If you want to do this, use 28 Ft. pounds. Torque wrenches can have error. The idea that you are going to "stretch" or damage the taper are well-meaning, but not a real-world worry if the tapers and fit are in good shape and fit well IME.

Some gorillas tighten cranks WAY too much, but if you are using a decent torque wrench then don't worry about it.
Back in my bikeshop days the factory assemblers used a very high torque. They were probably more worried about a buyer lawsuit if their crankarm fell off. I don't recall any problems from this, but it has been a while since I was assembling bikes in the trenches.

Andrew suggested 25 ft lbs for these particular cranks. Use that. 33.9 Nm.

They can all be made by the same folks or not, they have to be compatible and of the proper dimensions. Square taper BB spindles come in different lengths, and as pointed above (somewhere) some are also asymmetrical. So all being, TA, Shimano, Campy (are they still alive?) or Newman's Own, doesn't mean they will play nice, except maybe in Bolivia...