Techniques - Removing rusty screws

HarryMann: Threaded or self-tapping screws through sheet steel or bulkheads can be difficult to remove due rusted threads.

e.g. the four screws holding the heater box to the bulkhead protruding through to behind radiator area.

Whenever screw threads protrude and rust, first wire brush when dry (long single row ones are as handy as the big 'uns), then penoil. If they're of the No.3 size or larger and well supported (heavy metal behind), then might try an impact screwdriver to initially loosen. Screw back in a bit, repeat wire-brush/penoil, then work them out slowly. Once they're a bit loose can spray threads from front as well.

As we all know, half heartedly attacking with wrong screwdriver or not enough bodyweight behind it to start with, can be regretted in less time than it takes to find trhe right screwdriver or bit.

Another trick is to have someone tap the end of the screwdriver as you provide the torque. No result? Then grip better and get helper to tap harder (simulates an impact screwdriver).

Another take on it:

Scouse: I have a Devon conversion on my 2l aircooled, and the dam sky light is leaking. The roof is side lifting one, and the only place i can see where the water is coming from is a small crack in the rim where the screwa are positioned. Having used sealant and tape and it still leaks, I have taken the decision to remove the skylight and either refurbish it or replace it with another one i have obtained.

Can anybody advise the best way to remove the self tapper screws which have seized, and just round off, and do you think this is my only option.

HarryMann:

If there's any slots left at all, put some mole grips on the screwdriver and whilst forcing it in and 'gently' unscrewing repeatedly tap the end of the screwdriver with a hammer, a la impact driver method, tap fast and lever as the hammer strikes home (screwdrivers vary, not just in size but quality and fit of the head, which can usually be 'felt' straight away, either it feels like it will or it feels like it won't, in which case pickup another one of the right size and try that).

Sounds like you're past that stage, so just drill the heads off with sharp drill slightly larger than your estinmate of the thread size, then when all is off and accessible, with a small sharp drill, drill the screw out of the hole. Or, wind the thread out backwards with a pair of molegrips or good quality pliers.

The problem is often that the first thing to do is not to try to unscrew the screw. It is to get access to behind it, wire brush thread thoroughly and apply Plus-Gas or a 'good' pen. oil and leave for a while. Then, try to move the screw in either direction, try slightly tightening as well as slightly loosening, alternate then brush and pen. oil again when it first moves and unscrew in stages.

It's also sometimes possible to get a 'very good quality' pair of moles or mini-moles onto the self-tapper's head, work them to create opposing flats. Again, once it moves, alternate tightening and loosening in stages.