This is maybe not as daft a question as it seems:

Taking into consideration error margins that vary between torque wrenches and the quality of them, are there scenarios where it can be appropriate/ okay to tighten nuts to a torque a bit more than manufacturer specification?

I've a recurrent weeping leak on a component from the mating faces that have a rubber seal fitted internally.

The manual says the bolts for these mating faces should be tightened to 20Nm but it is obvious that the leak persists because the seal cannot be quite tight enough.

So, aside to theories that over tightening can actually lessen the effectiveness of gasket seals, if they're not making a full seal at manufacturer spec anyway, can there be any harm in increasing the torque setting, for example from 20-25 (which presumably is not so big an increase to cause what is quite a substantial bolt to snap)?
Thanks

Last edited by pld118 on 1st Mar 2015 4:39pm. Edited 2 times in total

Personally I am very reluctant to exceed recommended torque settings. The danger is, especially with alloy components, that you can induce stress fractures, which can not only lead to more leaks but the need to replace the item completely.

If you tighten to recommended setting and there is still a leak then, IMO, there is the probability that the seal is defective or the mating surfaces aren't true.

My take on it.

About a hundred years ago I had a Rover 75 six light saloon on which someone previous to me had over tightened the sump bolts. It used more oil than petrol!  John
2008 Stornoway Grey 3.6 Tdv8 Vogue
2005 TD6 Java Black Vogue - Written off!!
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MasseyFerguson 152 - No electronics!! - Sold

Last edited by pld118 on 1st Mar 2015 4:40pm. Edited 1 time in total

In which case I would be looking at the mating surfaces. A persistent leak is a right PITA. John
2008 Stornoway Grey 3.6 Tdv8 Vogue
2005 TD6 Java Black Vogue - Written off!!
GAP iiD BT
2003 Discovery TD5 Auto, Nanocom Evolution - gone to a new home!
MasseyFerguson 152 - No electronics!! - Sold

If you are 'handy' with spanners and have a bit of a feel for mechanical sympathy then not every bolt needs to be torqued.......I personally don't torque everything.

However, someone without any prior mechanical ability could easily strip threads, especially on smaller sized aluminium components. Stolen / Gone: 2006MY Supercharged LPG Autobiography - Zambezi Silver with Sand/Jet/Jet Oxford Leather.....