Any tips for cleaning the intake and exhaust valves of carbon deposits? Is there a coating somewhere that might be destroyed by a sodium hydroxide bath?
Carbon deposits on the TOP of valves are NOT anything to worry about or to mess with. The entire engine likely would be "destroyed" by a sodium hydroxide bath. Forget about this and move on to something else.
Dry ice blasting is the very best method to create near new like surfaces... Laser cleaners work as well, but vaporizing that much debris is not good to work around. But if you just want the valves done right you might want to find a shop that already has all the equipment to rebuild your head to look like brand new. It might be way cheaper than hours spent on the DIY way.
If you have the head off the block, you can remove the valves and use a wired wheel on a grinder to remove all the build up. That's how I do it. I did all my valve when I did the head gasket. If it's still on the block, a sharp chisel and scraping will do it. But you don't be able to get to all of the carbon on the back side of the valve.
As mentioned above the back side of the valve is where all the crud really builds up and is or can be critical.
I do have the valves out. The reason I'm trying to clean the undersides is so I can get the suction cups of a lapping tool to attach. The carbon on the intake valves is pretty soft and easy to remove with mild scuff pads without abrading the metal. The white residue on the exhaust valves (possibly burnt coolant) is really hard and unevenly deposited, and therefore poses more of a challenge.
Usually the brown Scotch bright pad is what we've always used in the shops along with the original safety clean green solution that'll eat your hands off which I don't think is available anymore I have 2 55 gallon drums left. I am certain it is no longer safety approved. But the Scott's bright pads on my die grinder with the adapter I think they're 3-in pads The brown is the one you want You whizz across that valve once or twice and it's silver or the original color and short order it will not be any going over this any amount of time literally zip zing next and that's pretty much it of course now I don't have the air compressor in the air tools they're predominantly electric. Still have the air tools don't have the big 4 cylinder compressor to go with the.
Invest in a wired wheel for a grinder, and a grinder if you don't have one. It will be worth it! It will save you HOURS of time and TONS of effort. Wear leather gloves. The wire on the wheel is NOT near at hard as the valve. I've cleaned a lot of valves this way with no damage. I clean the whole valve. You can use carb cleaner on the head. Then you can use valve grinding compound to seat in the valves.
