Lock-wire is a method of securing bolts. Wire is passed through a hole drilled in the bolt head and then twisted and attached to another bolt head or a hole drilled in the piece being bolted. Lock-wire will not prevent the bolt loosening the small amount where residual stress is lost. But it will prevent the fastener loosening completely and falling out. Also if the bolt breaks it should prevent the fastener falling out and the loose head creating havoc wherever it should fall.

The pliers are special. They self lock and the knob at the base of the handles is pulled out and causes the pliers to rotate, twisting the wire. (Click for larger picture). The wire is generally stainless steel. Lock-wire pliers are not essential, but are much easier to use than pointed nose pliers and give a perfect result.

Holes are drilled in each bolt head and the wire is twisted and positioned so as to tighten the bolts. For drilling the holes in the bolt heads a good center punch is required and the bolt must be clamped securely in a drill vice and the hole drilled on a drill press. Use the appropriate speed (about 2,200 rpm for a 2mm diameter drill) and lubricant. A cobalt drill will make the job easier, as most automotive bolts will be moderately hard. Deburr the hole and chamfer both sides. When wiring the idea is to get the wire tight by pulling it before twisting, not by excessive twisting. Practice makes perfect.

This image shows how to fit the wire for two or more bolts. If you imagine any of the three bolts trying to undo counter-clockwise you will see that the next bolt is tending to be tightened. They must be done that way. The wire goes in a diagonal direction to the next bolt, not just straight across to it. Use the correct stainless steel lock wire, not just any type of wire.

On the MGA all of the following are lock-wired:
Gearbox selector lever bolts.
Twin Cam sprocket bolts.
Twin Cam center support spindle.
Twin Cam nuts for the triangular support plates.

Do not use lockwashers. Loctite is not recommended (not required and not used by the factory). In hot conditions some grades of Loctite may liquefy and loosen the bolts. With chemical locking methods (Loctite etc.) becoming more advanced the use of lock-wire is now less common, but each method has its merits, so you must decide which is most appropriate.