How important are torque settings on bolts?

loofer

Was having a look at my Haynes Manual and on the section for removing the cylinder head cover (for example) it had the torque settings that the bolts should be tightened to.

How important is it to adhere to these? What if one doesn't have a torque wrench?

How much of a difference does it make if say you tightened the bolts as much as you possibly could?

If we take the example of replacing the cylinder head, how adverse would it be in each case if the bolts were more than or less than the specified torque settings?

marlot

Its vital, especially on a cylinder head which has to handle a lot of thermal stress.

The torque is set at a level enough to take the bolt into its elastic range, without going so far that it snaps.

wealdroam

It is important that they are all tight enough, and that they are all equally tight.
Overtightening weakens the bolt.

If you haven't got a torque wrench then get one or entrust the work to someone who has.

By asking your question it is probably clear that the second option above is the one to choose.

Wig

Very bad idea to do it without a torque wrench.

If you tighten as far as you can you will quite simply snap the bolts.

The bolts have to be tightened in stages all of them down to stage 1 then all down to stage 2 then all down to stage 3. If your bolts are not all at the same stage, some less, some more, you will not get an even seal on your head gasket (and risk leaks) & you increase the chances of snapping a bolt on the final stage.

Torque wrenches are not that expensive £25 ?

Money well spent IMO

optimus_primera

Don't take offence, but if you have to ask this question,then you shouldn't be doing a cylinder head off job just yet.
Start with the simpler stuff and work your way up.

mikey72

Not even that dear
£17

http://www.screwfix.com/prods/18289/Hand-Tools/Spanners-Wrenches/Wrenches/Reversible-Torque-Wrench

optimus_primera

Wig wrote: »

Very bad idea to do it without a torque wrench.

If you tighten as far as you can you will quite simply snap the bolts.

The bolts have to be tightened in stages all of them down to stage 1 then all down to stage 2 then all down to stage 3. If your bolts are not all at the same stage, some less, some more, you will not get an even seal on your head gasket (and risk leaks) & you increase the chances of snapping a bolt on the final stage.

Torque wrenches are not that expensive £25 ?

Money well spent IMO

A lot of bolts thesedays are torqued down to a low torque setting first, then have to be tightened using a Dial angle torque wrench.

Wig

optimus_primera wrote: »

Don't take offence, but if you have to ask this question,then you shouldn't be doing a cylinder head off job just yet.
Start with the simpler stuff and work your way up.

Depending on the car, (cheap and cheerful), I encourage the OP to go for it - with a torque wrench. And to ask here if he gets stuck on anything, post up pictures to help us to answer his problem.

myhooose

In my industry (hydraulics) torque settings are for lubricated threads not dry ones so I assume it is the same for the motor industry. I read somewhere it can make quite a bit of difference. But thinking about it the threads will be naturally lubricated on a used block anyway when removing the head.

If I remember correctly the order of tightening the cylinder head bolts is important too

Gloomendoom

If you do end up buying a 'clicky' type torque wrench (as opposed to the cheapo bendy bar type), remember to slack off the spring before you store it away. Otherwise, the spring will take a set and the calibration will be thrown out.

Wig

optimus_primera wrote: »

A lot of bolts thesedays are torqued down to a low torque setting first, then have to be tightened using a Dial angle torque wrench.

If the torque wrench bought does not have an angle gauge he can either buy one seperate (draper do one) or he can do the angle by eye. I don't have an angle gauge but I still manage to do it by eye. I bought a draper gauge but was not very impressed.

The OP has his Haynes manual so the instructions are there for him, he will need a torque wrench capable of the highest torque setting. Angles after that can be done by eye.