General Bolt Torque Settings

[apblake]

Does anyone know the general torque settings based on bolt size? I see all the specific torque settings in the service manual for specific bolts/nuts, but I don't see a general torque setting guide by bolt size anywhere in the manual...

[InnoCooperExport]

That's because it also depends what the bolt goes into. Any size bolt will need different torque when threaded into cast iron or if it's going in, say, aluminium. So there isn't a general guide based on size.

[apblake]

Totally get that, but some manuals give specs for any non-specified bolt (usually listed by bolt size). Unless I’m just missing it somewhere that means that they are not giving any torque specifications for all the bolts that are not listed (for example the engine Mount bolts).

[Peter Laidler]

Some of what you're asking cannot be answered specifically. It is called 'experience'. When it comes to torque, with experience, you just get a certain 'feel....' when it's right. And even then, after long apprenticeships and on the ground work and into uni, you still get it wrong - accasionally, but not often. That's what separates fitters or technicians and engineers from amateur enthusiasts.

[Ronnie]

This may help from a Snap On Torque Wrench manual

[111Robin]

The Snapon chart is a good reference but you need to take heed of the material grade and lubricant specified or you could exceed the allowable stress and while not shearing the fastener it could be close to the point of failure. As others mentioned you get a feel for when a fastener is "tight" from experience. I would only use a torque figure if it's specified in the manual as it will be for anything that does need a specific preload (eg. hub nut, head nut etc.). I wouldn't get too tied in knots with other miscellaneous fasteners. If you are concerned just set up a test piece and apply torque until you shear the fastener to give you an idea of how far you can go then do it again at 75% of the failure torque to let you see how it feels so you can judge it better.

[Dr S]

That’s why spanner’s are different sizes

[Polarsilver]

Agree with Robin .. However are you going to use "USED " Bolts that are possibly already stretched beyond their re-use & will be outside their design torque.. issue is using the correct specified Bolt for that application .. also not forgetting the correct grade Nuts of relevant type & any applicable Flat or Locking Washers & understanding if threads need lubrication .. i use Copperslip on most all threads..the exception engine mains & big ends.
Next question is the use of Loctite but that is not discussed in this thread and its use is very specific in my opinion.

[apblake]

Thanks everyone - super helpful - got a couple of other general torque spec docs from others as well.