So I thumped my head on a piece of plywood and a handful of rust scale came out. Anything else I can do to get rust out of my head before I put it back on?
Assuming you mean cylinder head I took about a foot of bicycle brake cable, chucked it in a drill and frayed the last couple inches of cable. It makes a flexible wire brush you can feed through the passages. Once everything is loosened up inside, blow it out with compressed air, just watch your eyes because they won't like flying rust.
If you don't mean cylinder head, consult a doctor.
Ignacio, i soaked mine overnight in a vinegar/water solution, and then took a pressure washer to all the available inlet/outlets. After it dried, i blew it out with the compressor. Its amazing the amount of crud that can accumulate in them.
I hate it when that happens. I know that tomato juice will slowly dissolve rust but will not hurt your head. Drink some Bloody Marys. HE HE. But really, setting it upside down and pouring some muriatic acid in it for a short while will clean it out. Just be really careful.
You could also;
Get it baked
Take to shop that does block acid cleaning
Soak in evaporust
Poke the sandblasting thru the holes and clean as much as you can.
Isn't this forum great, it's one place where one member can tell another to go soak his head and they don't get mad!
Once the water jacket of a head or block is cleaned, would it be worth treating the inside with one of the rust conversion chemicals?
If you're not in a rush, electrolysis works good.
Using a frayed piece of cable I was able to get a lot of rust out. Including a quarter sized flake.
At least one of the engine block passages was plugged with flakes and the cable opened it back up. Do the water passages extend under the valves of cylinder 1 and 2? I could not get the cable to go in. Is it plugged with debris or solid and there is no passage there? I found what looks like an ancient piece of rusting bailing wire in the water passages of the block. See picture.
I used a magnet pick-up on the back block water passage to get a lot of the rust out. Shaking and 'tumbling' the head made enough come out that I could not hear any more shards. The plan will be to get the head back on and do a final flush with the water hose. I cleaned the water inlet and outlet with a scotch wheel. The water inlet and outlet where the gasket goes is pitted. Will permatex #2 be sufficient to fill the pits so that the gasket does not leak?
The rotating cable is a good way to clean the water jackets (used with proper safety equipment of course)
The rusting piece of bailing wire is an original feature - they were used to position the sand cores when casting the block. Most of it was removed when the sand was cleaned out after casting, but some may remain - if they haven't rusted away after 90+ years.
If the head has a lot of rust in it that means the engine block does too. Make sure all the water passage holes in the head and block aren't stopped up.
The small 1/4" holes in the head and block are really important to clean out. Carefully use a 1/4" drill bit to clean out the holes. After years of use the holes can be almost closed.
Use air to blow out the water passages while you have the head off. You'll be surprised how much crud is in it.
Did the water passages go under the valves at cylinder 1 and 2? I cannot seem to get anything in or under there to clean rust out.
Yes, the passage goes under #1 & #2 valves also.