Best way to clean cast steel exhaust elbow?

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I have a Yanmar 4LH engine with a cast steel exhaust elbow that needs cleaning. The crud is hard carbon and it isn't really possible to get any kind of implement in to do a good job. I could do 'half a job' by poking around but I would like to do it properly while I am about it.

Could I use caustic? i.e. NaOH pearls. What concentration/temperature/time? The Yanmar elbow is protected on the outside with a silvery paint finish. I don't know whether this is just a finish or whether it is also passivisation. Can any suggest how best to finish the outside once the inside is clean? The colour doesn't not need to match in this position.
 
Hi David
Try the strongest oven cleaner ya can get - designed to remove carbon.. follow the instructions on the pack.
As for the outside.. hmm... try some galv paint - or better still exhaust paint from your local friendly car shop.. or - high temp paint designed for fires etc ...
ps, what happended with the black manky cable ?

Joe n Jayne
 
Joe, I've been soaking it in 5 litres of water with a teacup of NaOH pearls. The water is looking like gravy and the metal is still there. Will take a view tonight whether to leave it in soak overnight. It's so many years ago that I studied materials science and technology that I can't remember the the effect of NaOH in solution on cast carbon steel. I'm sure I'll be stuck here for a month if I have to wait for a new elbow....will order a spare this winter. I have cold galvanizing spray and will use that.

I couldn't get the tung oil but bought some Turtle Wax car tyre stuff. I think that it will work but I haven't done the whole length yet as we are plugged in. The Spanish give you very funny looks if you ask for tung oil - even in Spanish. Try it for a laugh.
 
We use to use castic soda to restor the heads on old britsh bikes, its was fine on cast steel and the phosphor bronze valve guides but sometimes took a few days changing the soution daily. Stove black is fine for paint the water injection means they dont run a normal exhaust temp.
 
Thanks, mine has been stewing all night and nothing more is happening so I will refresh the solution. The metal looks fine to the eye. I was worried in case the caustic could cause the carbon to come out of the steel - I am ignorant of the chemistry of this and haven't found anything of any practical use on the Internet.

To have heads on a bike would be a great convenience. Makes you wonder how the pesky Japs cornered the market /forums/images/graemlins/wink.gif
 
OK, so it is all clean and back together again. For the benefit of anyone searching on this problem in the future.......

The caustic did absolutely nothing of value other and risked getting caustic all over the deck. Oven cleaner was just as useless even after heating the elbow in an oven. So I bought a cheap Dremel clone with a big box of cheap 'tools' and used cutting blades, grinding wheels and a miniature reamer to grind, cut and ream off the carbon. I managed to get it to the stage where though not perfect is 98% like new inside.

Getting it all back together again was pretty easy. I put liquid glycerine soap on the hoses and they went back on very easily.

On starting the engine, the flow of water seems better but that wasn't really the point, I had had to remove the muffler to replace it and that required the elbow to come off to get the hoses off - I couldn't possibly have put the elbow back on again in that condition.
 
Try some hydrochloric acid? Should just spray on and eat through the deposits. A chemist will confirm it to be ok, but I would have thought it should be fine as it is ok on aluminium and stainless. Concentration approx 20% or less.
 
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