J B Bell

So, I joined the "up past midnight" bike-repair club last night, replacing the crankset on my touring bike. Gigantic pain in the ass, though rewarding. Safety tip: beware of youtube videos. They show the chain off for instructional convenience (just drop it onto the bb tube), and seem to underplay the rather massive force required to remove these things.

My question, griping aside, is how necessary is a torque wrench? The crank bolts specify about 40 Nm, and I translated this to "go ahead and give 'er, you're not big & strong enough to over-torque this." I based that on my truly remarkable experience removing the bloody things. (A 10 cm. hex wrench does not provide much leverage.)

Should I be bothering with a torque wrench, or is "really damn tight" an adequate measure for a crank bolt on a square spindle?

maddmaxx 

This is the one bolt on the bike where you are probably quite safe.

Peek the Geek

agreed.

Retro Grouch 

40 Nm = 30 Lb/ft (roughly). Imagine a 30 pound weight hanging off the end of a foot long wrench. Tighten your crank bolts that much.

BCRider

Oddly enough long time mechanics seldom use a torque wrench except for really serious stuff like balancing the torques on head bolts and similar jobs.

But they have learned the "feel" such as RG mentions above.

twobikes

This question rages back and forth regularly through multiple threads. Some claim they can feel the right torque range after years of practice, and then you read that someone checked out such people to discover they are often not nearly as close to the specs. as they thought they were. If you do not use a torque wrench and it works for you (no broken bolts, does not come apart on the road), well and good. What more is necessary?

I personally like to use a torque wrench. I made my own from a dial indicator fisherman's scale (about $5 at Wal-Mart) and a steel bar a bit more than 10 inches long. The scale reads up to 50 pounds, so at 10 inches between the scale attachment point and the hex key you have the possibility of 500 inch pounds. (The Park Tool web site has a conversion chart you can download for converting inch pounds to Newton meters.) Your bolt would be in the neighborhood of 350 inch pounds.

I did discover that my scale reads six percent light. That means I would over-torque. I shortened the 10 inch distance by six percent to compensate. I usually use it to tighten the collar on my carbon seat post.

Retro Grouch 

Most people who have driven cars for a few years think they have a pretty good "feel" for 35 MPH. So how come everybody instinctively checks their speedometer whenever they see a police car?

HillRider

Bravo!

San Rensho 

For cars and motos I use a torque wrench on almost everything. Perfectly clean, oiled threads and a torque wrench I can honestly say I have never stripped anything, had anything fall of or had anything leak and everything comes apart very easily.

On a bicycle, I rarely use one. Maybe occassionally on the crank bolts or the rear axle nuts on the track bike. The problem with most bike fasteners, the small ones, is the danger of overtightening. I use one of those 3 in one allen or socket tools where its pretty hard to overtorque the fastener.

I guess if I had carbon bits, I'd use one because of fear of cracking something, but I'm a good ten years away from getting some of that untested, new-fangled carbon fiber stuff, so thats not a consideration.

fosmith

one of the tech guys at giant told one of the techs at my shop, "You're a mechanic...you know what tight is!" funny, but should be true.

operator

The only real places you need a torque wrench is for carbon parts. The rest an exprienced mechanic can do by well, experience.

Bottomfeeder

I depend on a torque wrench for certain things. Take modern sealed bottom brackets, for example. The non drive side cup needs to hold the bottom bracket in the shell with just enough force. Too loose and the BB will loosen and begin to work out of the frame. Too tight, and it will bind the bearings, making it harder to pedal and causing premature wear. I make sure to torque the cups to the manufacturer's spec's, at least initially. Then if you want to go a little tighter, or a little looser, depending on how things feel fine.

DanO

bkaapcke

40 nm, or 30 foot lbs. isn't really all that tight. Yeah, overdoing it on crank bolts won't toast anything. But, for some of us, the main utility of a torque wrench is to prevent overtightening things. On CF bikes, this is critical. bk

operator

Overdoing crank bolts can result in snapped and stuck bolts -

kpfeif

On the crank bolts maybe not, but you should probably have one around...

https://www.pezcyclingnews.com/?pg=fu...72&status=True

neilG

You'd think. I was a professional bike mechanic for a lot of years and rarely used a torque wrench (ALWAYS on crank bolts, BTW) even after I had starting using some carbon parts, namely a CF faceplate on a stem. Thought it was about time to do it "correctly", used the torque wrench on the faceplate bolts and promptly cracked it. Shoulda left it alone.

HillRider

Experience is a wonderful thing. It lets you recognize a mistake when you make it again.

The torque wrench debate is one of the few things I used to disagree with Sheldon Brown about. He said a torque wrench wasn't needed by an experienced mechanic, and in his case, he may have been right. However most of us have less experience and, in many cases MUCH less experience, than he did. Using a torque wrench is never a mistake and can avoid some serious problems during the learning process.

neilG's experience with the carbon face plate just shows manufacturer's specs aren't always right either.

Retro Grouch 

By far the greater problem with crank bolts is under torqueing and the resulting hosed crank arms. I'd be willing to check 100 bikes at random and give you $1.00 for each crank bolt that's over torqued if you'll give me $1.00 for every one we find that's under torqued. I'm so confident, to make it sporting I'll pay you in Canadian dollars and let you pay me in USD.

operator

ROFL.

Yes the only reason I brought that up was because a customer came in the other day. He said that his crank bolt snapped.

My first thought: WTF
Next thought - he overightened it by himself. I know because I did the work on his bike, and I used a torque wrench on crank bolts, like I do on every build/repair. That's the one place I regularly use a torque wrench. The 8mm/14mm socket is nearly permanently attached to it.

It ended up cheaper to replace the bb with the bolt still stuck in it than to charge $50/hour to try and get the bolt out. Although it might've been much less expensive than replacing a right crankarm or the whole crankset.

Al1943

I cracked an $850 CF fork steer tube because I used a torque wrench and the torque specs shown on the stem- would not have happened it I'd just used a 1/4" drive ratchet and my intuition.

On the other hand I didn't use a torque wrench on the Italian bottom bracket which subsequently unthreaded itself. Re-set it with a torque wrench and no more problems.

And no, I don't get paid to wrench.

Al

operator

What CF fork costs $850. Seriously.

HillRider

I believe the toque specs engraved on stem steerer clamps and handlebar clamps are intended for steel or Al steerers and handlebars. They certainly were in the past and may have been modified now that carbon is so common.

I also wondered, what fork costs $850?

BCRider

The special one with the crack in the carbon matrix obviously.... SHEESH!

Trekbikedude

Blackbox sid?

jstraw97

I just put a new wheelset on my bike not 30 minutes ago, so I have to ask, is it possible to over torque a cassette lockring?

An $850 dollar fork?