Using a cheap allen key is usually a waste of time as they are usually far too weak and can damage the Allen socket in the head of the bolt with repeated attempts:
You will need to use a decent hexagon bit like this
(but the correct size for the bolts):
I place the bit into each of the bolts and then give it a few good taps directly on the end with a small hammer to try and shock the bolts loose from the cover before attempting to undo them.
I sometimes use a pair of mole grips on the shaft of the bit to allow the bit to be turned anticlockwise and tapped with the hammer simultaneously for really stubborn bolts.
In extreme cases, I've also applied a small amount of grinding paste inside the bolt's hexagon before inserting the bit, as this provides additional grip between the bolt and the bit to help prevent the Allen bit from spinning inside a badly worn hexagon.
If the hexagon is completely knackered, you may be able to find a suitable sized Torq bit
(slightly larger than the worn hexagon) that can be hammered in:
Other ways of removal include using a hammer and centre punch to gradually drift the bolt head in a clockwise direction until it comes undone
or mig welding the inside threaded portion of a suitable sized nut directly onto the head of the bolt and then undoing it with a spanner.
Drilling the bolt out is usually my last resort, especially if it is threaded into an aluminium component.
Alan
