Piff 

Though I am aware that square taper crank installation technique has many different camps and can start lively discussion ​​​​​​, I'd still love to hear some opinions.

Recently, I noticed that one of my bikes has a wobbly chain line and creaky noises coming from below. The chainline smoothly deviates laterally back and forth as you run the crank, and squawks when extra torque is applied. After a little online reading, I figured the crank bolts must be loose. They were. Unfortunately, I have ridden like this to the point that the crank sqaure taper is too rounded to properly tighten. Even if I reset the taper and crank it down farther it will begin to creak a little bit after a ride or two.

I ordered some new cranks and would like to avoid messing them up again. My only problem is that I don't have a torque wrench. And, when installing cranks prior, I always felt like you could just continue tightening the bolt onto the crank on and on and on if you really wanted to...which I understand to be a no-no as well.

​​​​​​So, do you guys have any advice on the feeling of when to stop when installing square taper cranks with a peanut butter wrench? Thanks. JIS taper, if that makes any difference.

Jeff Wills

I've used torque wrenches on crank bolts but it's been years since I had one. I don't have one now but my square-taper cranks don't loosen.

Here's what I do when I tighten cranks now: position the wrench and the crankarm 30 to 45 degrees apart. Squeeze the crankarm and wrench together with both hands and arms- be careful not scissor your fingers off. It should take a significant push, that is, the wrench should leave an indentation in your hand. I honestly don't think you can overtorque this bolt with just a peanut butter wrench.

I grease the threads and rotating surfaces of the bolt. I don't grease the tapers but then I don't clean oil off them either.

3alarmer 

.
...there are, indeed, endless discussions on this forum on this topic. My own experience is that you'd need to be a gorilla to over tighten the crank bolts using one of those peanut butter wrenches. So if that's what you're using, hit it with whatever strength you have in your hands and forearms. I think there was a Jobst Brandt discussion about how all the stuff about the cranks sliding on too far onto the tapers is bunk. Generally, metal taper fits, (even aluminum alloy cranks,) don't work that way. Also, the cranks often loosen up in the re-seating process after about 50 or 100 miles, so it's never out of place to re-torque at that point, then leave them alone.

I, too, grease the bolt threads lightly. I'm not shy about torquing them and I've had good luck without a torque wrench. I've done the tapers both dry and with light grease. I don't think it makes any difference.

I've seen many cranks ruined by bad pulling practices (at the co-op). I've never seen one ruined by over-torquing.

merziac

99.9 no torque wrench for me, only when an arm may be trying to bottom out. That being said, as with all mechanics there is a feel or "touch" in these cases, auto wheel bearings, all of our bike cup and cone and on and on. I am not shy about tightening these, a regular ratchet or dedicated crank bolt wrench gets most of what I can give it with light and or residual lube.

If you think about how much force it takes to remove a properly seated crank arm, that can temper your install if you have the experience to convert it.

Never had one come loose or need retorque, maybe mine are too tight.

Piff 

Fantastic, thanks for the advice. Looks like I can use my peanut butter wrench relatively worry-free as long as I make sure to give it a good push.

merziac

You realize we may just be getting started, right?

Piff 

As long as it helps pass the time till my cranks arrive
​​​​​​

Bianchigirll 

Back when I worked in shops we never used them. I am sure they around but you just tightened it until it was tight. I was taught in Aviation Fundamentals at Millington TN (anyone else been that charming campus?) that in general a proper wrench used correctly will proved all the torque needed. Of course there are exceptions like engine parts and engine and bomb rack mountings. If your 10mm wrench was as long as your 17 you’re more likely to strip things.

randyjawa 

Most comments I offer are based on personal experience and, trust me, you can over push a tapered fit. I did so, many years ago, and was shocked to hear "snap". Investigation revealed the drive side Mavic SS crank had split. It happened only one time, to me, but I have seen other alloy cranks that failed in a similar fashion.

Being a professional mechanic, I tend to see value in using the proper tools. Having and using a torque wrench is a good idea and, as others have mentioned, be sure to check the taper fit after a few miles. I do this three or four times, after a crank installation, then I install the dust caps and, pretty much, forget about it. Also...

Lubricated or dry does make a difference in a taper fit. So does putting grease on threaded fits. When I used to install bearings at work, and some of those bearings needed a crane to lift, I paid absolute attention to the engineer's/manufacturer's specifications for installation. Some say lube it up, others insist on dry fit.

Anyway, there goes another few minutes of self imposed isolation.

jeirvine 

This. Peanut butter wrench and bare hands, as tight as you can get it. Never had a crank come loos, or crack from over-tightening. The wrench is that length for a reason: just the right amount of torque.

ThermionicScott 

Okay, I’ll bite: a torque wrench good enough for the job is only $20. I use it for so many other things, I don’t understand the resistance some have to even owning one.

lostarchitect 

I have a torque wrench (3 of them, actually) but have never used it for crank bolts. Never had one loosen up or break, either.

unworthy1

Also the P-butter wrenches have a thin sharp-edged handle (also short in length) all of which add to auto-torque-limiting! If you try to tighten past a certain torque-point they do more than "leave a mark" in your palm. All that aside there's times I don't have the right P-B wrench at hand so used a socket on either a ratchet or some other handle, and I don't know if I ever stopped to get a torque wrench out (even tho I own several of various sizes)..YMMV but I have never split a square taper crank arm or ruined the taper-hole....yet...and I ofttimes have LIGHTLY greased the taper flats, as often as done it "dry"

Road Fan

I'll join in as wingman - I used to have the bad habit of going around my bike with the set of combination wrenches and feel for looseness a few weeks after I had built a bike. I usualy felt some give in the bolt or nut after "proper installation," so I concluded it had backed out a bit. After a while some bolts, like seatpost clamp bolts, snapped. Back in those days a new Campy was not too dear, but they could be hard to find, even in Chicago. So once I had taken a Strength of Materials class in Eng School, I realized I done bad, and one reasonably reliable way to not do bad again that way was to use a torque wrench, not to rabidly crank it down, but to use the elasticity of the steel to put on enough tension that inter-thread friction (and at the other interfaces) would be adequate to resist unscrewing, but not so much that I forced the bolt into inelastic deformation - do that and it's likely to break after a fairly short time.

The last torque wrench I bought was about $90 from Craftsman (about 20 years ago), but it replaced three that had cost about $12 each, Buffalo and the like. And while it took all three cheap ones to cover my range, the newer one covers all but one, fixed cups. Plus, I like click-type rather than dial-type.

So I use a torque wrench not to make so tight God cannot get it undone, but so that his junior angel here doesn't break things very often! Am I a pro? No. Am I an incompetent? No. I just like to play with bike parts and frames without breaking things.

steve sumner

it's a learned "feel". it took a couple of years in a LBS till I had it. when trying to describe to
younger mechanics the best I could come up with was: just a hair less than as tight as you
can go with a socket on 10 inch handle. as already stated you can't over tighten with the PB
wrench, on the other hand it might not be quite enough. for new cranks retighten every 60 miles
3 times.

cb400

A cheap beam torque wrench has been a great investment for me. If I were to start building engines I'd make sure of the accuracy. It also works well as a breaker bar, the freewheels I've removed came off without much effort, I expect it will work equally well to remove bottom bracket cups. Without one I'd worry about having the same problem as above since I am not the strongest person.

63rickert

The Campy seatpost bolt broke easily. Not your fault. They were hard to find because shops did not order them, knowing they would break.

A shop story I have told before. It’s almost thirty years so I will name names. And the shop is long gone. Shop mechanics sometimes get ideas and run with them. This happened at Alberto’s in Hubbard Woods. Alberto knew better of course but he was tired of the game and was in process of selling to one of his employees. The mechanics decided that crank bolts should not loosen. Customers normally neglected the 30 day free service and then there would be a problem later. So they decided to get them real tight. With a pipe extension on a socket handle. Before the madness ended they were putting full mechanic weight on end of a four foot pipe. So maybe 800 ft- pounds of torque. Lots of bolts broke and had to be EZ-outed. Some cranks broke on the spot. Some cranks broke later. Most cranks survived. That any crank survived is kinda surprising. But if you overdo it at home and get 50 or even 80 pounds out of your PB wrench nothing bad is going to happen.

Road Fan

Well, I didn't say I snapped a crank bolt, and in fact I didn't. Seatpost binders and some others, yes.

RiddleOfSteel

A dial type torque wrench is as stated above $20 or possibly even cheaper. I have some clicker types, but the dial is reliable and needs no special storage care like the clickers.

When I first set out on this grown-up cycling thing, I definitely used a torque wrench as I didn't know the values for various BBs and crank bolts. I gained a feel and use a combination of wrenches depending on the BB and crank situation. For crank bolts, it's a standard Craftsman 3/8" drive ratcheting wrench and a 14mm socket (or 15mm, whatever the bolt is). I put the bike on the ground (with wheels and tires on...) after spinning the bolt finger tight, get the left hand on the crank arm and the right hand on the wrench, and press down on both. Lift up on both and repeat the pressing down until I feel it get nice and tight. With that wrench and my weight/strength, it's around 25 lb-ft as per spec. BB cups get the big 12" crescent wrench employed with varying delicacy/force to achieve appropriate torque and away I go. I lube the tapers now as well as any threading. Haven't had a problem so long as I spin the wrench in the right direction...

3alarmer 

...+1. I am offended that someone would write that I'm offended at the thought of buying yet another tool.

Reynolds 

Not to hijack this thread, but IMO some seatpost binders break not for overtightening but because they bend when using a loose fitting seatpost.

merziac

That too, but no and not overtightening per se, these have crappy plating on the threads that galls/seizes when they start to get tight, then snap "I don't want to tighten anymore".

Seen many competent wrenches break them with both original and proper post and bolt.

I apply a slight amount of anti-seize, never broken one yet.

Salamandrine 

Craftsman 3/8" drive ratchet wrench was the defacto standard tool for this when I was wrenching BITD. That's what was pretty much always used for fixing crank bolts. If you were lucky there was a Snap-on ratchet wrench too. Usually there was a peanut butter wrench around but no one used them, ever, except maybe for peanut butter. Torque wrenches were around but only used rarely. When I was training new mechanics, I'd usually make them use a torque wrench for the first couple months, until they got a feel for what 25 ft/lbs felt like.

I think most home mechanics would be well served by getting and using a torque wrench.

If you use a peanut butter wrench, like everyone says, get it as tight as you can, and you'll be in the ballpark.

I don't have the energy today to discuss what should and should not be greased.

merziac

Who you callin a "grown up"?

I have a dozen torque wrenches, rarely use for the bikes, but.....

SurferRosa

After installing cranks, I always ride the bike a block up my hilly street and around some flat blocks for a few minutes. Then I tighten one final time, never to touch it again until the bb needs service.

When installing, I like to use my wrench hand halfway up the socket wrench for most of the tightening. I do the final bit by feel.

Fine tuning also depends on the bike, the age/model/condition/group level of the bb/crankset and the purpose of the build. I'm a little more aggressive with lower level stuff for flips, for example.