Torque wrench or not?

[Paulus]

Not being a trained engineer, I have only used a torque wrench once when replacing a head gasket on my Ford Anglia. I thought it might be prudent to torque the cylinder head down to the prescribed amount.
With everything else I work on the do it up finger tight, and then give it half a turn with a spanner.
Never really gone wrong with this approach.

 

[TC99]

I'm thinking of getting one. Temu have a few around twenty quid.

 

[ColinJ]

I am going to improvise one using an old 30 cm steel seatpost and a couple of large plastic milk bottles full of water. I reckon that 4.5 litres of water at 30 cm should give me the 13 Nm that I need for my Hollowtech crank bolts?

That will work for the crank bolts but there are other bolts which are in awkward positions/orientations from which it would be difficult or impossible to get the seatpost allen key extension horizontal. The spring balance idea would be better!

I have just converted one bike to Hollowtech II. After reading this yesterday...

I also saw a guy who'd stopped and gone back to fetch something he'd dropped in the road. As I approached he picked it up and held it up for his friend to see. It was his left crank .

... I decided that I had better make my DIY torque wrench and make sure that the bolts are correctly torqued! Change of design though.

This is what I have done this evening:

The allen key is inserted at the left end of an old steel seat post. The RH jubilee clip is positioned to set the limit of movement for the LH one. The handle of the 7.5 kg kettlebell will be pushed up to the LH side of the LH clip. I have calculated that the max offset needed is 18 cm from the head of the bolt in order to apply ~13 Nm of torque.

Test time tomorrow (Thursday)! I will start off with the LH clip where it is and alternately tighten the crank bolts, then move the clip another cm or so nearer to the limit and so on, stopping after tightening one last time with the clips touching.

I had done the bolts up fairly tight without using the extension on the shortish allen key. I'll be very interested to see how much tighter the correct torque actually is!

 

[ColinJ]

Torque of the town
I just used my new DIY tool and discovered that it may have one or two shortcomings!

• Hanging a 7.5 kg kettlebell off a steel tube on one side of a bike does tend to make the bike topple over
• Allen keys are hexagonal in cross-section so their angle can only be adjusted 60 degrees at a time. This means that it is pot luck to be able to get the key and extension tube horizontal, which the torque calculation was based on.
• It is very silly! That has never stopped me in the past of course... (As another CJ might have said "I didn't get where I am today by being the kind of man who doesn't do what I do"!)

Anyways... It worked well enough to show me that the bolts were at least 25% undertorqued. They both tightened by at least a quarter of a turn with the correct torque applied.

I will either buy a torque wrench or use a spring balance to pull on the extension post.

 

[Dogtrousers]

• It is very silly! That has never stopped me in the past of course...

And please don't let it stop you in future!

 

[T4tomo]

As brilliantly flawed and entertaining as @ColinJ's approach is, I can recommend Topeak's relatively cheap TW. granted it only does 5-12nm, but 40nm crank bolts and BB's etc is really just "as tight you can"

 

[Punkawallah]

I use an automotive ‘beam bar’ for any torque settings. Reasonable priced and seems to work (when I need it).

 

[chriswoody]

I've dithered for years over whether I really need a torque wrench or not, now my Kona runs a Race Face crank that needs a massive 61nm of torque to fasten. Up till recently I'd just cranked the bolt up tight and left it at that. Then it started giving me a lot of grief, the retaining bolt kept working loose, because I failed to properly torque it up to the 61 nm the last time I'd reassembled it, not matter what I tried I couldn't get it. to tighten.

So I finally descended down the rabbit hole of looking at Torque wrenches and purchased a generic automotive 10 - 110 nm torque wrench for all of the high torque fasteners, including the 54nm SRAM cranks on the mountain bike. It's not a massive fancy pants digital one, but a descent click style wrench that should help avoid causing any more damage in the future.

I'm probably going to try and find a 2-15nm range one for the lower torque ones later in the year when I have a little more money.