15-08-2019, 07:17 AM
Completely rigid joints fully tightend do not loosen - there's the nub of it (though I think I'd have said 'correctly' tightened).
In the modern motor industry bolted joints and tightening torques are taken very seriously. Any joint with potentially injurious consequences of failure is individually tested to determine the correct torque, it doesn't come from a look-up table. Any subsequent change to the joint - the plating of the bolt for example - is grounds to re-test. Compliance in a joint is a recipe for subsequent torque relaxation - the joint slowly compresses and the bolt comes loose. Spring washers are avoided, they might stop a nut from dropping off but only when the joint has already come loose - when tight it is no different from a thick plain washer. But also because - like self-locking nuts - their influence in the joint is inconsistent. They introduce variation into the relationship between applied torque and clamping force, making the joint tightening characteristics less predictable. The best way is a plain nut (and plain washer, where appropriate) with the correct torque applied.
Things are different for amateur restorers, we don't have test labs at our disposal, nor are our parts or assembly conditions consistent in any meaningful way. A spring washer doesn't do any harm and I for one use self-locking nuts frequently.
Nylocs used anywhere critical (e.g. big ends) should be used once only. Not so sure about bolts, I don't replace my big end bolts but they are probably a bit different from most used in A7's.
In the modern motor industry bolted joints and tightening torques are taken very seriously. Any joint with potentially injurious consequences of failure is individually tested to determine the correct torque, it doesn't come from a look-up table. Any subsequent change to the joint - the plating of the bolt for example - is grounds to re-test. Compliance in a joint is a recipe for subsequent torque relaxation - the joint slowly compresses and the bolt comes loose. Spring washers are avoided, they might stop a nut from dropping off but only when the joint has already come loose - when tight it is no different from a thick plain washer. But also because - like self-locking nuts - their influence in the joint is inconsistent. They introduce variation into the relationship between applied torque and clamping force, making the joint tightening characteristics less predictable. The best way is a plain nut (and plain washer, where appropriate) with the correct torque applied.
Things are different for amateur restorers, we don't have test labs at our disposal, nor are our parts or assembly conditions consistent in any meaningful way. A spring washer doesn't do any harm and I for one use self-locking nuts frequently.
Nylocs used anywhere critical (e.g. big ends) should be used once only. Not so sure about bolts, I don't replace my big end bolts but they are probably a bit different from most used in A7's.