Chemically disolving black gunge.

On 20/10/2017 11:37, T i m wrote:

No easy answer IMHO. Certainly no chemical "magic bullet".
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T i m wrote:

CBY to trawl through all the replies but try EGR Valve Cleaner (Exhaust gas recirculating) These get coked up with tarry carbon and possible very similar to your valve/cylinder head.
Bob
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On Fri, 20 Oct 2017 18:02:19 +0100, Bob Minchin

Actually, that does look quite like to sort of carbony gunge I'm seeing so that could be another thing worth a go, thanks. ;-)
Cheers, T i m
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T i m wrote:

Another possibility might be the stuff used to clean cooker/oven parts. It is a liquid that you dunk shelves, burners etc in. I think it is used cold and must be fairly "frisky" to burned on carbon and yet presumably benign to metals. I think it is called Oven Pride but not sure as it is not in my "department".
I'm a bit concerned that this compressor seems to have been run so hot that it would burn the oil. My compressor does get hot - too hot to keep my hand on but that should not decompose oil.
Bob
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On 20/10/2017 19:13, Bob Minchin wrote:

Beware, this may contain sodium hydroxide. see my earlier posts
Malcolm
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Malcolm Race wrote:

It is possible Malcolm but compared with the dire warnings on the now banned "Kleen-off" which was NaOH in a gel, this stuff has less warnings and at the same time we have been more H&S conscious, so I'm minded to think it might be OK with metal bearing in mind that many hob burner parts are diecast aluminium.
Bob
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On 20/10/2017 19:21, Malcolm Race wrote:

It may, except Chrome is dissolved by sodium hydroxide, so not sure if it will for a oven cleaning product also targetting chrome wire shelves?
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On 20/10/17 20:58, Fredxxx wrote:

????
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On 21/10/2017 01:01, Tjoepstil wrote:

Are you suggesting that shiny oven shelves are not made of chromed steel?
Don't you think any oven cleaning product might be careful how much sodium hydroxide they put into their magic formula?
Just in case you don't know: https://www.wikihow.com/Remove-Chrome-Plating
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I'd hope they are SS these days.
Remember seeing a barbecue with chrome plated grills. Didn't last long and soon became a rusty mess.
--
*When the going gets tough, the tough take a coffee break *

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On 21/10/2017 11:35, Dave Plowman (News) wrote:

I'm sure you're right. Just a thought.
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On 21/10/17 11:56, Fredxxx wrote:

Well sometimes I aqctually learn something new here. It appears that chrome is dissolved by caustic, but *very slowly* which is a good thing because I have been using caustic to clean fatty gunk off chrome since forever.
With no apparent ill effects.,
--
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On Fri, 20 Oct 2017 19:13:56 +0100, Bob Minchin

Ah yes, I've used such bought from the Poundshop to (quite effectively) to clean the grilles from our oven. I think you mixed up the chemical, tipped it into a big Ziplok bag, added the metalwork and then moved it about a bit to 'coat' all the metal bits then leave it for a while to do it's stuff. You then took the metal bits out and they were all clean and shiny. ;-)

Me too.

The thing is, these particular 'silent' compressors only have a 50:50 duty cycle with a maximum on time of 30 mins. So, let's say it was being run hard (a worse duty cycle) and using the older mineral(?) oil then I'm wondering if it was a possible cause of it starting to coke / sludge up.
As soon as that happens, some carbon get under the (fairly light) reed valve and it not make pressure, even if not being used it would then run continuously (and silently) and could therefore run pretty hot and for a long time?
The rest of the guts 'look' ok, the bore isn't scored and there doesn't appear to be any crank / gudgeon / big-end noise and because it was so lacking in oil (and obvious signs of being opened), a good chance any oil that was in there was still in there when they noticed it wasn't working was tipped out rather than burnt out.
The oil is drawn up the wet sump though the spinning crankshaft / armature and then just spray lubricated all the bits at the top (big end, piston / bore, top bearing etc).
The bits in question can be seen on the bottom half of the 'Pump Diagram' page (4) seen on the link below:
https://www.bambi-air.co.uk/uploads/files/2016/07/Budget%20Handbook.pdf
The reed valves in question are either side of the 'Valve plate' (item 26). One is just trapped against the gasket and held in place with two dowel pins but the other is held down under the raised 'horseshoe' / end stop you can see in the diagram. This would allow that reed to 'open' about 2-3 mm at the top of the 'U' before being restrained by said plate. The ends of the retaining plate are riveted to the main valve plate and it's that bit I'm trying not to disassemble (by drilling out the rivets, cleaning and possibly re-setting the 'spring' in the reed and re-assembling using countersunk machine screws and possibly locking nuts (not sure the nylon would survive the heat in a Nylock nut)?
Cheers, T i m
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T i m wrote:

Given the warnings in the manual about ensuring no leaks to avoid damage, it seems that the 50:50 is a warning to the user not to exceed 50:50 duty rather than saying the compressor itself is controlled to run at max 50:50. I wonder if the thermal trip device has failed shut and that a leak present has meant the unit has cooked itself. Modern copper wire has a very high temperature enamel so possibly not a concern but could have led mineral oil to burn. Bob
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On Fri, 20 Oct 2017 20:55:58 +0100, Bob Minchin

Correct.

That was my thought / fear Bob. ;-(

TBF, the only sign of anything untoward is this buildup on the *outside* of the valve plate and inside of the cylinder head (if that means anything to anyone).
The air is drawn in via a sort of plenum chamber us sucked into the head via the reed inside the valve plate and then blown back out though the horseshoe reed, round the head and back out though another manifold / reservoir chamber, before being discharged out through the delivery pipe to the reservoir (though a non return valve).
As the piston is ringless, they predict a certain amount of oil bypassing the piston and so getting into the cylinder and potentially out though the output reed / head.
Cheers, T i m
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