richeydog

Hello. A few days ago I replaced a square taper bottom bracket and re-installed the crankset(Exage 400lx) with a socket wrench. I got it as tight as I could and did sense that it was moving into place onto the spindle. But I'm not sure if it was tight enough.

I haven't ridden it yet because I'm paranoid about damaging to the crank arm. Because of that, I am borrowing a torque wrench from my brother.

Here's the dumb/noob question: Can I check the torque with the already tightened bolts? Or do I have to unloosen the bolt and/or take off the cranks and start anew with the torque wrench?

corrado33

With the bolt already tightened, if you have the torque wrench set at X Nm or Ft lbs, the bolt will be AT LEAST that tight, not accounting for static friction. (Which isn't that much and shouldn't throw your measurement off that much.)

So yes, you can, but the bolt could be overtightened and you wouldn't know it. Safest thing to do would be to loosen the bolt and tighten it again.

FBinNY 

If the bolt is under torqued significantly and turns as you come to torque all is good.

If you come to the torque reading without the bolt moving there ate three possibilities.

1- over torqued already,
2- torqued to spec
3- under torqued, but close enough that the dry friction is enough to fool the torque wrench.

So if it it doesn't move, consider the third possibility, and loosen then properly tighten coming to the torque spec in one continuous motion.


If you're curious, you might tighten to 90% of torque spec, stop then retorque and see if the static friction is high enough to fool the torque wrench when you're 10% short.

Homebrew01

If the torque wrench handle is significantly longer or shorter than your regular wrench, tighten to 85-90 % with the torque wrench. Then give a last "oomph" with your socket wrench to get a feel for the correct tightness.

Bill Kapaun

I wouldn't loosen it, just to retorque. If it's over torqued, it'll just stay that way. Any possible damage is already done.

I would recheck the torque after riding. Just in case things "settled in".

Ronno6

Can the crank bolt be accurately re-torqued without pulling the crankarm off the spindle??
If the bolt is currently over-torqued, would the crankarm not be driven onto the spindle in excess?

Just wondering.

richeydog

Thanks for the advice.

I'm following Park Tool's recommendations for tightness. Torque Specifications and Concepts | Park Tool

It tells me the Crank bolt tightness (including spline-type cranks and square-spindle cranks) should be between 305–391 IN-LB, or 25 to 32 FT-LBs.

Is this still valid?

Flinstone

Hunh, static friction is generally a huge correction between bolt tension and torque (never mind the thread pitch etc anyway.) But specified torque is specified torque, and accounts for all that, unless you've got rust or something. As for at being "at least" that tight, I don't get it. Again, the only meaningful meaning of "that tight" is torque without getting into tension, and the toque is what the wrench says it is, unless there's something wrong with the wrench. I don't know why you'd expect it to be in general more than the wrench says it is. Do all torque wrenches read low?

bykemike 

Read a bit on this subject, you want dynamic torque and not static torque. A good example is the checking of automotive or motorcycle headbolts , always back them off,one at a time, and retorque.

Without backing off first you really have no clue as to what may be holding the bolt (locktite,rust?) or is the bolt too tight? For the few seconds extra it takes to back off before torqueing it is worth it.

rmfnla

My thought as well, but I tend to try to avoid over-thinking such things...

Andrew R Stewart 

Two good points here mentioned. To check torque on previously tightened fittings- slightly loosen the retighten to spec. The VERY good suggestion to check torque after an initial use or three (and use point one when doing this). I find the 'set it "right" and forget it' path to be one often with roots to trip over. Andy.

79pmooney

Careful. The old gospel was that after you tightened the crank, then rode it, the crank would lever against the edge of the bolt which would shove it a tiny amount further on to the taper. (Especially if you rode hard.) So you check the torque. It's low. You tighten to spec. And ride again. Same thing. The crank wedges on further. You tighten again. And keep doping this until the crank splits at the corners of the taper and falls off. Or you have permanently enlarged the taper and weakened the crank.

I've seen cranks broken that way but never heard the story. I play it safe. Get the crank on tight and leave it until it is time to take it off or i have reason to thnk there is a problem.

Ben

richeydog

I see.

What's the maximum torque a person could achieve with a socket wrench? The wrench in question is 6-3/4 long.

richeydog

With the bolts tight, I set the torque wrench on it at 30 ft-lbs. The left arm seemed to move a little before the wrench clicked. The right arm(drive side) didn't show noticeable movement before clicking out.

Andrew R Stewart 

Ben- Many wrenches will take issue with your method and description. To suggest that the crank arm will lever against the retaining bolt/nut and further move up the spindle is not what some feel is really happening.

Instead as the arm is worked over the spindle with pedaling forces the arm's hole slightly opens up. There is no driving force moving it up the taper of the spindle (other then over tightening, a different force then you focus on). But this slight molding of the arm's taper to that of the spindle's causes a possible slop to develop in time. It is this opening up of the arm's fit to the spindle that causes the arm to, in time and cycles of use, fall off. At no time does the arm want to move up the spindle's taper (unless the bolt/nut is further tightened).

So the need to re torque the retaining bolt/nut is an initial bedding in follow up. Once this initial break in is done and compensated for (by the small amount of re torqueing of the retaining bolt/nut) little later maintenance is needed.

It's common for the LH arm retaining bolt/nut to need more tightening after initial use then the RH side does. By a larger amount... Andy.

Homebrew01

Depends how heavy you are. Max torque is when both feet are off the ground.

kevindsingleton 

It depends how strong you are. I can exert far more force than my weight!

corrado33

It's a bike. It's close enough. Seriously. Yes the static friction will cause your torque wrench to read a bit high until you break it loose but again... I reiterate, it's a bike, it's close enough.

So, rewording my statement since you obviously didn't understand. If you set a torque wrench at 10 N*m, check an already tightened bolt, and the torque wrench indicates it's at torque. One of two things is happening. 1. The bolt is tighter than 10 N*m. 2. The bolt is almost at 10 N*m and the static friction is making the torque wrench read slightly high.

Either case it's fine. It's a bike. It's not that big of a deal.

habilis

True, but only if you have something to push against. With a socket wrench, the natural way to produce maximum force is by pushing straight down on a horizontally positioned handle. In that case, the maximum force is limited by your weight. A 6-3/4" handle is about half a foot long, so a 200lb man bearing down on it is exerting slightly over 100ft/lbs of force before he lifts himself off the ground. If you need more force, you'd need a longer handle.

"Give me a fulcrum and lever long enough, and I can move the Earth." - Archimedes

kevindsingleton 

Well, now, that's not entirely true. It would still take 200 lbs of force to lift a 200 lbs man, but I get what you're saying!

The Earth is already moving, Archie! Math nerds! Sheesh!

habilis

The nerd is exerting 200lbs of force on himself but only 100ft/lbs of torque on the bolt.

kevindsingleton 

I'm not even sure that works. If he applied the 200 lbs directly to the bolt (no wrench) it's 200 lbs. Extending that reach out 6 inches doesn't reduce the force.

corrado33

You guys are both ignoring what happens if you jump or hop while putting pressure on the lever. I often do this to loosen lugnuts on cars. I generally have to do this when using any wrench/ratchet less than a foot. Put the socket on it, stand on the bar, then hop a bit. Works every time. (Yes, I'm a light person.)

kevindsingleton 

That's a little too advanced for this discussion! For that, you'd probably have to measure force in metric, or Kardashian, or something!

andr0id

Looking forward to OP's next thread....

What new crank should I buy?