5nm Roof bar Allen key

[otherclive]

My grandson has ordered a set of roof bars for his 5 series saloon. They are the type that fit directly to threaded holes in the roof. The instructions say 5nm which is a low torque. When he asked me I told him do up by hand then a gentle *** with an Allen key. Over tightening the bolts that go into the cars roof could risk loosening the captive nuts and then that’s that.

I hand tighten mine on to fixed roof rails and use a Draper 10mm socket (screw) driver for a final ***.

He clearly didn’t feel too comfortable with grandads advice and has been looking at 5nm Allen key wrenches pre calibrated to 5nm. Are these any good?

 

[Jcloughie]

Well, what do you know!

 

[otherclive]

n*p……..i. I’ve been cancelled by software guardians.

 

[Guzzilazz]

I had a motorcycle with a cam cover that was held in place by three shoulder bolts. The shoulder went through the cam cover (sealed by a rubber/metal washer). The shoulder was there to snug up against the thread within the alloy cylinder head. 5 Nm was the normal torque, and I bought a low value torque wrench. When I removed the bolts, one of them sheared (???) and the other two the thread on the bolt was "waisted" (i.e. the threaded part had been stretched due to overtightening). Fortunately, there was enough of the bolt near the top of the head to enable me to use a tiny screwdriver to undo it enough to remove. A 6" long ring was far too much to tighten the bolts.

Buy the right gear to do the job!

 

[Dustydog]

The worry is that they may loosen and come off.
Why not use Loctite on the threads? Belts and braces.

 

[otherclive]

I had a motorcycle with a cam cover that was held in place by three shoulder bolts. The shoulder went through the cam cover (sealed by a rubber/metal washer). The shoulder was there to snug up against the thread within the alloy cylinder head. 5 Nm was the normal torque, and I bought a low value torque wrench. When I removed the bolts, one of them sheared (???) and the other two the thread on the bolt was "waisted" (i.e. the threaded part had been stretched due to overtightening). Fortunately, there was enough of the bolt near the top of the head to enable me to use a tiny screwdriver to undo it enough to remove. A 6" long ring was far too much to tighten the bolts.

Buy the right gear to do the job!

But what is the right gear for torquing up his roof bars to 5nm. The question I posed was related to these tools that are preset Allen, or socket heads, won’t say calibrated as it may upset some.

 

[Dustydog]

I suppose this would do as it measures from 2nm.
What happened to the days of feel and dare I say FT?

 

[otherclive]

The worry is that they may loosen and come off.
Why not use Loctite on the threads? Belts and braces.

As these aren’t permanent fixtures they are removed as the roof bars come off. I did consider Loctite, but my norm in such cases would be a dab of Fernox. Sets firm-flexible and easy to remove. They may come with spring washers, if not I have hundreds, or may have anti rotation compound on the threads. The captive nut in the cars roof may be nyloc. I advised him that next car should have raised roof rails with an air gap underneaths. Makes fitting bars so much easier.

 

[otherclive]

I suppose this would do as it measures from 2nm.
What happened to the days of feel and dare I say FT?

My approach at such low torque is as per your second sentence, and check after 25 miles…..just after you have checked that the caravan wheels are still tight 😱

PS no link in your post

 

[GaryB]

I had these on a 2016 5 series BMW, the threaded holes under the flaps in the roof tracks were full of paint and I had to re-tap them to get the bolts in! I didn't use a torque wrench and they were fine, BUT a word of warning, the feet on the roof bars I had (Halfords I think) actually just touched the flaps when they were raised to fit the roof bars and one of them actually snapped at the hinge.

 

[Hutch]

If your son is talking about this type of torque wrench, then yes they are fine. Myself I prefer " hand tight" but that's with over 55 years of hands on working on engines and aircraft.
Torque wrench

Remember, two clicks and a 1/4 turn strips threads.

 

[otherclive]

I had these on a 2016 5 series BMW, the threaded holes under the flaps in the roof tracks were full of paint and I had to re-tap them to get the bolts in! I didn't use a torque wrench and they were fine, BUT a word of warning, the feet on the roof bars I had (Halfords I think) actually just touched the flaps when they were raised to fit the roof bars and one of them actually snapped at the hinge.

Thanks that answers one of his questions to me. The fitting instructions show a bolt going into the cars fitting then the bolt being discarded to a dustbin. Must admit that schematic puzzled me at first.

 

[otherclive]

If your son is talking about this type of torque wrench, then yes they are fine. Myself I prefer " hand tight" but that's with over 55 years of hands on working on engines and aircraft.
Torque wrench

Remember, two clicks and a 1/4 turn strips threads.

Thanks, my grandson now has the bars and he’s going to Halfords to buy a similar preset torque wrench at 5nm from the bicycle department. I do mine up hand tight with a screwdriver and a 10mm socket fitted. Difference I guess between an engineer or someone well versed in cars, motorbikes, etc and someone who isn’t. But better he, cautious than over confident. I don’t want my roof box spilling out over the A1.

 

[Lutz]

5Nm is just over 3½ ft lbs. I would have thought that's fairly easy to judge manually. It's about what one can just comfortably achieve pulling with one finger at the end of the 5mm Allen key.

 

[Hutch]

Lowest torque setting 4nm.

 

[otherclive]

Lowest torque setting 4nm.

View attachment 7583

Thanks. What does it go up to? I’m always a bit cautious using tools or instruments at one end or other of their range. Especially if the range is quite wide. Although Wright are a good make.

 

[GaryB]

A few years back I worked for a company and part of the products used specialised bolts where the torque was critical. We proved during testing that the absolute maximum you could generate with a straight handle grip (screwdriver type - no additional leverage force) was around 7Nm, no matter how much "grunt" was applied. OK a bit more than the 5Nm needed here but it was a bit of an eye opener, especially when the company Gorilla scoffed that he'd out-perform everyone else and failed!

 

[otherclive]

5Nm is just over 3½ ft lbs. I would have thought that's fairly easy to judge manually. It's about what one can just comfortably achieve pulling with one finger at the end of the 5mm Allen key.

You’re an engineer not a lawyer who hasn’t grown up fixing push bikes, motor bikes or early cars. 😂
I’m sure few know the link between a 5mm Allen key and one finger.

 

[otherclive]

A few years back I worked for a company and part of the products used specialised bolts where the torque was critical. We proved during testing that the absolute maximum you could generate with a straight handle grip (screwdriver type - no additional leverage force) was around 7Nm, no matter how much "grunt" was applied. OK a bit more than the 5Nm needed here but it was a bit of an eye opener, especially when the company Gorilla scoffed that he'd out-perform everyone else and failed!

That’s an interesting observation. Thank you.

 

[Hutch]

Thanks. What does it go up to? I’m always a bit cautious using tools or instruments at one end or other of their range. Especially if the range is quite wide. Although Wright are a good make.

Max torque. 22. Nm or 200 inch lbs.