Chemically disolving black gunge.

Hi all,
I'm helping a mate who has just bought a second hand silent compressor (on my recommendation) and the one he bought was know faulty, 'spares or repair' etc.
On testing there was no output (as advertised) but long-short, I partially stripped it (someone had been there before me) and found the reed valved and 'cylinder head' had a fair amount of carbon build up on them.
One reed just sits on a couple of location pins so can be removed and it and it's seats cleaned easily but the other is trapped behind a support (that manages the maximum opening) so I can't really get in / under that to clean it all.
I've had it in an ultrasonic cleaning tank at 60 DegC and whilst it did seem to remove (or soften) quite a lot of it, I'm not sure that it is properly cleaned in all the little crevices.
So, to the chemists probably, is there a reasonably 'safe' / chemical way I could remove this black stuff (carbonised mineral oil deposits?) without melting my fingers or the alloy / steel parts or should I drill the rivets out, strip it down and cleaning it mechanically (the stuff does scrape off reasonably easily from those bits now) and re-attach it with some small nuts and bolts?
Cheers, T i m
p.s. It may be that the fixed reed is bent slightly so might need removing to reset, or it could simply be held up slightly by said deposits. If it makes the compressor work, mate would invest in a service kit but they aren't cheap.
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On 20/10/2017 11:37, T i m wrote:

Caustic soda is used for decarbonising two stroke exhausts. It wont harm the metal.
Cheers
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Clive

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On 20/10/2017 12:18, Clive Arthur wrote:

I woul be very wary of using caustic soda (sodium hydtoxide) as it attacks aliminium and I would suspect that it might attack aluminium alloys.At best I would apply a drop if solution to a an area where corrosion would not be a problem. Be aware that dissolving caustic soda solid in water releases a large amount of heat. It also attacks skin so wear gloves and goggles
Malcolm
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^^^^^ I assume that's aluminium alloy.

I assume those exhausts are just steel, not "alloy / steel". It won't harm the steel.

It does. One method of last resort for removing stuck aluminium alloy seatposts from steel bike frames is to dissolve the seatpost with caustic soda.
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On 20 Oct 2017 13:05:12 +0100 (BST), Alan Braggins

Sorry, yes, it's an 'aluminium head and I have no idea if it / how it is alloyed. ;-)

Good tip. ;-)
FWIW, I'm currently experimenting with the steel reed block in some 'Soda Crystals' (Sodium carbonate decahydrate) as we had some here. Is that likely to do anything as one of the uses it mentions on the packet is to clean pans, hobs and BBQ stuff (that sound like a carbon type of buildup)?
Cheers, T i m
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On 20/10/17 13:56, T i m wrote:

caustic will dissolve olefins - that is members of the CnHm format that are not too polymerised. It does that by sticking an OH on one end of the chain, thus rendering the olefins into soluble detergent.
Insofar as the black gunge is in fact hydrocarbon, it will remove it. However if it's pure carbon, it won't, and what you need there is red hot oxygen.
Tht will simply oxidise it and probably rust the steel a bit at the same time.
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wrote:
<snip> >I woul be very wary of using caustic soda (sodium hydtoxide) as it

Thanks for the cautions Malcolm.
FWIW we had a bag of 'Soda crystals' that we put a spoonful of in the washing machine now and again and that suggests it can also be used for cleaning BBQ stuff. It (as you say) also cautions against allowing it in contact with aluminium so I've just put the steel reed valve block in the solution for now. ;-)
If that does get damaged somehow it would be fully replaced in a service kit (so we have little to lose etc).
Cheers, T i m
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T i m wrote:

Sodium hydroxide (caustic soda)and soda crystals (sodium carbonate)are different.

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On 20/10/2017 14:13, FMurtz wrote:

Soda crystals are more commonly known as washing soda (sodium carbonate decahydrate). This gives an alkaline solution which will attack aluminium but not as vigorously as caustic soda
Malcolm

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wrote:
<snip> >Soda crystals are more commonly known as washing soda (sodium carbonate

So, would it still have a similar cleaning effect for my needs?
Cheers, T i m
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On 20/10/2017 15:20, T i m wrote:

I honestly don't know.. It does attack aluminium so try a patch test on an unimportant area. It will attasck aluminium foil, albet slowly (immersing a tarnished piece of silver in a solution of washing soda containing aluminium foil will clean the silver converting the silver compounds back to silver. It is the chemical reaction between the silver and aluminium which does the work)
Malcolm should have said I have a chemistry degree and taught the subject for a considerable number of years
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On 20/10/17 13:24, T i m wrote:

That a is sodium carbonate. Almost completely useless at anything, but safe for muppets to have in their possession.
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It pongs as well. I suppose if one is not sure of the materials its a bit awkward on how to advise on a suitable solvent. Brian
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On Fri, 20 Oct 2017 12:18:46 +0100, Clive Arthur

Good idea, thanks, I'll give it a go. ;-)
Cheers, T i m
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On 20/10/2017 12:18, Clive Arthur wrote:

Depends a lot what the metal is. Steel won't but aluminium alloys will dissolve rapidly in caustic soda and some engines are made of that.
I'd be inclined to try some combination of white spirit and Swarfega to soften the carbonised black gunge.
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On Fri, 20 Oct 2017 13:50:34 +0100 (GMT+01:00), jim <k> wrote:
<snip> >> So, to the chemists probably, is there a reasonably 'safe' / chemical

That's a good thought and I have a can here. I'll give it a try and it would also be good for blasting any bits away from under the reed valve etc.
I'll see what it looks like once out of the washing soda soak. ;-)
Cheers, T i m
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On 20/10/2017 13:59, T i m wrote:

Isnt there something to remove carbon etc from car Airflow sensors/gauges ? Seem to remember some advice when I replaced the one on my old diesel Golf .
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Commonly called carburettor cleaner. Dissolves all the gunk you get with burning petrol and oil. And is safe on most metals and plastics etc as found in a car.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Dave Plowman (News) wrote:

There is also brake cleaner but the real stuff (the one with(Tetrachloroethylene and Methylene Chloride is a bit hairy to use.(with heat it can make phosgene.)
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Carburettor cleaner. From any decent car accessory shop.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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