Tightening Nuts To Torque

[FarmerPug]

How important is this, its just when i was following the haynes manual to change the front spring i found it a bit hard to follow, it keeps referring to tighten to the specified torque, which it puts on a table a few pages back, why not just quote the right torque there in the sentence, surely "xx NM" takes up less space than "the specified torque"

I was then looking at the same repair on one of them Ebay cd repair guides and its unit of mesurements dont seem to be right it talks about 9 Dia Nm, whats that all about, and some figures are different from haynes.

So apart from putting a head back onto the engine when is tightening to the exact torque, how important is it for other bolts?

[boombang]

The torque rating could be listed for three reasons:

1. So you don't under tighten - the nut could work loose or allow increased movement, causing increased wear and potentially fractured bolts.
2. So you don't over tighten - if you do is risks either snapping the bolt or stretching the threads, could again work lose.
3. To retain a component with the correct pressure - sure as steering racks, bearings etc, where they may require some load to keep fastened but too much would stop them working correctly.


Suspension strut top bolts for example, if you've used new nyloc nuts then doing up by feel is perfectly acceptable SO LONG as you're ideal of feel is realistic. I've spend best part of 15 years working with cars, both hobby and professionally, I use a torque wrench for anything appropriate and feel for most other things.

[boombang]

To try and explain the differences, there are pretty standard torque guidelines for a given bolt diameter. This then varies significantly on application, tensile rating of bolt/nut, pitch of thread etc.

One source you use might have standard ratings for that particular nut/bolt setup, the other may be taking from manufacturer manuals.

Haynes probably say "the specified torque" to make it simpler for changes to the manuals. If a torque rating changed between editions, they would then just be updating a table. More likely though is it's damn easy to have all the torque ratings in one place. For most jobs I would never look at the how to, but would be likely to check torque rating.

[jasper5]

Basically, Haynes will tell you to tighten to the specified torque as a disclaimer, they will list all the specified torque setting at the end of the chapter you are referring to when you read the guide on doing the job.

Personally, as a vastly experienced mechanic, I very rarely use a torque wrench....I can tighten a bolt to the correct torque by feel, even a cylinder head or big end bearing.

[boombang]

[Welly]

I use my own guide, gathered from years of things falling off or shearing suddenly:

It's quite simple; some Nuts are 'Nipped' up, others are 'Murdered'

[jasper5]

After 43 years I feel I can tighten a bolt up with great success

[lozz]

Ive not used a torque wrench in about 10yrs,

Torque wrenches are for Meat heads that dont know there own strength,

[Busman]

Ive not used a torque wrench in about 10yrs,

Torque wrenches are for Meat heads that dont know there own strength,

Or people who wish to comply with the law in comercial vehicle garages!

[Bailes1992]

Use a torque wrench for important things like wheel bolts, hub nuts, caliper bolts etc etc.

Tend to do allot of things by feel too.

[hammerman]

Even though i just replace my front springs & struts,i did`nt use my torque wrench on anything.I trust my own strength & feel.Other wise i would`nt be doing 100 miles a day down the motorway to work & back.
Even though i`m a digger driver,i do a fair bit of running repairs etc on my machines.Nothing is ever torqued up,& these are big 55mm+ nuts & bolts on mega ££££$$$$$$$ money machines.Never had any problems.

[lozz]

Igot afew mates, that own garages, ipop in time to time,
never seen them use atorque wrench, Mainly its all air-tools,

one chap iknew that worked for vauxhall got fired because a timing belt tensioner had failed on acustomer,
he had used the torque wrench, but they didnt beleive him, so are they Acurate anyway, (id say most are not)

ive never snapped abolt, only the ones on exhaust heat sheilds, (rusty things)
so idont use a torque wrench,

if it was alegal requirement in the trade, then why dont tyre fitters use them instead of sending you on your way with bolts your going to struggle getting off
withought a breaker bar, or needing to buy new wheel bolts coz theyve stripped the threads,

[Bailes1992]

Igot afew mates, that own garages, ipop in time to time,
never seen them use atorque wrench, Mainly its all air-tools,

one chap iknew that worked for vauxhall got fired because a timing belt tensioner had failed on acustomer,
he had used the torque wrench, but they didnt beleive him, so are they Acurate anyway, (id say most are not)

ive never snapped abolt, only the ones on exhaust heat sheilds, (rusty things)
so idont use a torque wrench,

if it was alegal requirement in the trade, then why dont tyre fitters use them instead of sending you on your way with bolts your going to struggle getting off
withought a breaker bar, or needing to buy new wheel bolts coz theyve stripped the threads,

All the garages I go to for new tyres always use a torque wrench?

Torque wrenches have to be calibrated regularly to maintain their accuracy.I've got a small torque wrench designed specifically for torquing up spark plugs.
Got to service the Pug in the next few weeks so just sent it off to be calibrated.

[Busman]

Took the works car into kwick fit the other day, and even they used a torque wrench!

[Bailes1992]

Another reason I use a torque wrench is that I'm a bit more confident that the bolts aren't going to come undone afterwards.

I picked up a new 1/2" Torque wrench today as mine is siezed up.

Clarke torque wrench that goes upto 210nm... £23 in Machine mart!
Cheaper than the amount it costs to have them calibrated! (£28).

I think at that price you can't afford not to torque up bolts!

I've also got an old 1/2" one with a dial. It has a bendy kneck and as it bends it shows the amount of torque on the dial.