Dean Ngan

Hi guys I'm new to this forum

So basically I went to the mechanic today to get my squeaky drivetrain checked and they took out my crankset (Shimano 105) to regrease it.

After they were done they put it back, but to my horror, they did not use a torque wrench to tighten the left crank arm fixing bolts (sorry I couldn't post a picture as this is my first post) as mentioned in the instructions: "The two left crank arm fixing bolts should be tightened at the same time rather than each fully tightened separately. A torque wrench should be used to check that the tightening torques are within the range of 12 - 14 N·m {105 - 122 in. lbs.}."

What they did was they just used regular allen keys to tighten the bolts in an alternating manner. I rode the bike afterwards and they did not seem to be loose.

What I'm concerned about is whether they overtightened it, and whether that would cause any problems now or in the future.

Should I be worried about this? Any advice would be very much greatly appreciated

Thank you so much in advance Cheers!

aclinjury

if the mech is using an allen key that's 4in long, I doubt that he'll be able to over torque 12-14 Nm. You don't really need to use a torque wrench for metal stuff unless you're a gorilla.
Only time I'd even think about using a torque wrench is for the following carbon items: stem, handlebars, steerer.

Having said that, I don't use a torque wrench myself, at all. But I do have a good feeling what 4 Nm feel like in my fingers when using an allen key. Generally, using 2 fingers firm pressure gets you close to 4 Nm, and that's all you really need, carry an allen key for the first few rides in case components slip so you can re-tighten. Thru trial and error, you'll soon learn just when enough is enough.

The mechanics, having wrench a lot, they know how much is enough. No reason to distrust a mechanic with even a few months of experience in torqueing bicycle bolts. This isn't rocket science.

GlennR

They should use a torque wrench. You should check it to ensure it's not too tight or too loose.

Over the winter I serviced my bottom bracket and used a torque wrench to reassemble. On my second ride the left crank arm fell off.


The flange on the alloy fixing bolt sheered off.


Th torque spec is printed on the fixing bolt in ft-lbs and Nm. I must of set my torque wrench to ft-lbs but used the Nm number, so I over torqued it.

Luckily I was not out of the saddle when it came apart.

So i replace the part, torqued it to the correct number and have 3000 miles since.

jadocs

Technically they should use a torque wrench, but when someone does it for a living they are usually pretty good getting it within range by hand. I wouldn't worry too much.

topflightpro

They should use a torque wrench. I disagree with the assertion that people who do it for a living are good at feeling a torque range.

aclinjury

The thing about "precision" (and I use this term loosely) tools is... if you use them, you have to regularly calibrate them.
So to those who preach using a torque wrench religiously, how often do you calibrate them?
I'm guess... never?

aclinjury

how do dentists screw down implants and crowns? Do they use any torque wrench? Nope. They go by feel. Tight enough is tight enough. When in doubt, just err on the softer side and bring an allen wrench for the first few rides.

GlennR

I have a friend that owns a machine shop and I give them to him to have checked yearly.


Since I build a half dozen engines a year, I take care of my tools.

aclinjury

great that you have access to resources that can calibrate free for you.
What about for those home bicycle mechanics who don't have such free access?
I'm sure they're not going to want pay a fee to calibrate? Fee could be more then the worth of their tool.
I have a friend who runs a professional calibration business; they calibrate expensive things like Fluks and o-scopes, equipments in the tens of thousands. You'd be surprised that if left to their own, many of these equipment owners would almost never bother to remember calibrate their stuff, and they use their tools on a daily in much more critical applications. You'd think they'd be religious about their calibration.

But my point is that, if you're going to use cheap "precision" tool (yes, a bicycle torque wrench is cheap stuff) and you don't plan to calibrate it regularly, then you might as well just go by feel, err on the soft side, and bring an allen wrench for the first few rides.

frogman

Its foolish to go by feel and "assume" you have the torque you want. Most machine shops can check and adjust the calibration on your torque wrench. Its an easy thing for them to do. There are several in our town that do. Not hard to get it calibrated locally. I have my torque wrenches calibrated yearly.

GlennR

I work on aircooled VWs as a hobby for the past 45 years and have seen more M6 studs ripped out of the magnesium engine case from owners tightening them by "feel". Luckily I found a source for m6/m7 step studs since the m6/m8 don't leave enough material in some places.

I bet 99.99% of bike shops use the Park or Shimano torque wrench and never have them calibrated. But I bet they are a lot close than 99.99% of those that do it by hand.

Also having the "right" torque wrench is important since most are less accurate at the extremes. That's why I have 4 of them.

alcjphil

Not mentioned so far is the importance of making sure that both bolts are tightened to the same torque value. Even if the calibration of the torque wrench is off a bit, the bolts will have been tightened equally which is very important

Barry2 

Welcome to BF.
Sometimes it's just nice to work on your own stuff.
For the cost of a torque wrench, you get a lifetime of comfort.

I'm an IT guy... I tell customers "if you don't trust your IT guy, get a new IT guy"

Same could be said of your bike mechanic.
I trust me to reach for the torque wrench every time.
Re-cabled my bike this weekend, I know all the cable pinch bolts are at the correct torque.

Barry

GlennR

Do you know of the bar and stem bolts at the correct torque when you're racing down a hill at 45mph?

Trek sells a 5Nm torque key for $20 that will check the bars, stem, seatpost and brake calipers.

ThermionicScott 

I don't spend much time on the Samba anymore -- glad to see you still have a hand in it!

ThermionicScott 

That doesn't follow at all. A torque wrench that might be 10% out is still way better than a person who might be up or down 50% depending on how they're feeling that day.

GlennR

Or over tighten and it snaps. That's usually the case.

OUCH

dabac

I’ve got a length of flat bar with an 1/2” square hole cut at one end and a 3/8” hole at the other. I attach the bar to the torque wrench so that it protrudes horizontally, support the wrench on a table and hang what I consider a known weight off the other end of the bar and see what happens.
While I’m not going to be printing any calibration certificates anytime soon, I’m reasonably confident that differences in thread friction have a greater influence on the torque I’m actually getting than the error in the tool as such.
How often - I haven’t logged that. When the mood takes me. When waiting for an application of epoxy resin to cure. Or the chain wax to melt. About yearly I’d say.

fietsbob

Reading a service/overhaul manual they give you a torque specification. To follow directions accurately,
You need a torque wrench offering the same numbers .
Thereby, "How Tight" is assigned a Standardized Number..

Barry2 

Tighten until it snaps, then backoff 1/2 turn.

Barry

Dean Ngan

Thanks so much for your advice everyone, really appreciate it

​​​

philbob57

Mine sure does. If yours doesn't, wow!

GlennR

So did mine... he's my brother-in-law.

royphotog

Working on an old KLR 650 motorcycle years ago I was not using a torque wrench and fighting a water pump bold, I was not dealing well that day and that may have been the issue, but a torque wrench would have prevented the little snap of the shaft that the 10mm threaded end lived on. I can still feel that little snap. Luckily I was able to find that shaft on eBay for a reasonable price.

msu2001la

How does one calibrate a torque wrench, and how far off from the displayed number can they actually be?

I own several different varieties, the one I use the most on my bike for seatpost, stem, handlebars, etc is similar to this one:
https://www.parktool.com/product/adj...Torque%20Tools

I also have another larger one that I bought at a hardware store that measures torque at higher levels for things like cranks.

It's never occurred to me to be concerned about the calibration on either.