Ideas wanted fo unseizing grub screws in aluminium

[Chris Green]

Yes, I wondered about nylon, it would certainly address the corrosion problem. The only question would be if they can 'pull' hard enough.

[The Natural Philosopher]

Ah, why didn't you say 'clamps' instead of 'wedges'

If they are still made, why not get new ones and grind the old ones off?

PS in a marine environment, its a race whether aluminium degrades faster than steel.

[Joe]

Marine? Have you tried removing alloy wheels from steel hubs after a few years in fairly mild inland weather? Yes, I dropped the car (gently and with precautions) onto the wheel after removing the bolts. Not a sign of movement.

I followed the advice of the Internet, and used progressively larger chunks of timber to bash the wheel on alternate sides, and eventually it came loose.

Not a trace of salt...

[Chris Green]

The Natural Philosopher [e-mail] wrote: [snip]

Because they're a cross between the two! :-)

I was very surprised to find that the *were* still made. They're over £2 each so if I can re-use some it will save me some money. There's well over a hundred of them on eight windows.

This is inland waterway rather than sea, but it's still wet. :-)

[Thomas Prufer]

I'm finding stuff called "marine-grade anti-seize"... one has zinc in it and says "for threaded steel parts assembled in aluminum or zinc castings" (LOCTITE® LB 8044, zinc dust plus petrolatum.)

I'd add a wrap of PTFE tape, and maybe use hex grub screws?

Thomas Prufer

[Chris Green]

I can only find that from US suppliers, I've not spent a long time searching yet though so I may eventually find a UK/EU supplier.

I already have hex drive grub screws to replace the stupid slotted ones that were originally used.

[David]

The photos make things much clearer.

This is very much a drastic solution. If you can get an angle grinder cutting blade underneath the wedge, cut through the screw.

This should allow the wedge to fall out.

Then put the wedge in some hot oil and leave to soak. With a bit of luck the screw should then be removable.

[Chris Green]

This is what I did on the first few, however some can't be reached with an angle grinder. Knocking them out with a hammer has worked pretty well on the less accessible ones. Thus removing them isn't really the issue.

It does! :-)

Any old oil? I can certainly try this when I get home. I was just hoping there might be some specific sort of hot liquid that would work well.

[The Natural Philosopher]

No, by that time the salt was in fact gone. The corrosion in the alloys is Aluminium oxide .

Normally that protects the aluminium from chemical attack, BUT it seems that any conductive water in combination with two different metals will produce an electrochemical reaction that strips the oxygen out of the water lets the hydrogen go free and oxidises the two metals.

So it's not the salt per se that does the damage, its *any* conductive ions in the water.

...makes a fascinating read, if you are interested.,

[The Natural Philosopher]

The zinc is there to 'take the heat' in the same way it does in a galvanised steel situation It meeds to be in contact to work, so the PTFE is an alternative, not a supplement

[David]

Any mineral oil would do. You don't need the latest (and expensive) synthetic oil. At a pinch, you could even try cooking oil.

Also after soaking the wedge in the hot oil, try removing the old screw while hot - the aluminium should have expanded more than the steel screw which should make removal easier.

[Thomas Prufer]

I'd use any "anti-seize". I got a tube of some mix of grease, copper, graphite, and magic stuff (ceramic? MoS?). A very little goes a long way, and it stains.

Come to think of it: would a hex head bolt work, with the head towards the bulkhead? More head to get purchase on, when it comes to removing it? (ugly, though).

Thomas Prufer

[Chris Green]

Thanks for all the ideas folks.

I can report *some* success, I realised that in many cases the grub screws projected enough to get a half nut and then a full nut onto them. By locking the nuts very tightly together I have managed to remove four (out of seven I've taken from the current window) of the grub screws.

The grub screws are surprisingly clean (the ones I've removed anyway). I think maybe the corrosion was more from where they bear on the steel superstructure than due to nearby aluminium.

Of the remaining three still stuck grub screws only one has any usable thread, the other two really have corroded away to a craggy stump.

The grub screws are steel, or they're magnetic anyway and not stainless because they drilled our fairly easily.

So I think my main search now is for suitable anti-seize compound.

[Smolley]

I like the idea of PTFE tape.

[alan_m]

If you need to apply heat consider

[Chris Green]

Thomas, that is brilliant! There's enough (but not a lot to spare) clearance for the head to rotate and it makes for a much larger bearing surface apart from anything else. Appearance doesn't matter, the whole thing is pretty ugly and will be hidden by insulation/lining anyway.

Thank you, lateral thinking rules OK! :-)

[Joe]

I understand the chemistry, I was pointing out that the extremely high conductivity of salt water was not necessary for some very good corrosion, the very weak acidity of rainwater was quite sufficient.

[Andy Burns]

Nylon or some other plastic set-screws as replacements?

[Andy Burns]

Last time I was in that predicament, I did have a bug lump of wood in the car, and a club hammer, no joy, ended-up reinstalling the bolts, but not very tight, driving round a supermarket car park doing heavy braking, eventually freed the wheel from the hub.

[Chris Green]

I've wondered about this but I'm not sure that nylon would be strong enough, the windows have to be pulled pretty tight against the seals to make them watertight.