What's the preferred, non-chemical/non-additive method for removing oil sludge from an engine that's still installed in the vehicle? I'll have the head and oil pan removed. How do I clean out the oil galleries and other passages in the block without damaging the surface finishes?
Lots of elbow grease.
Really, if you don't want to use chemicals, you are stuck with using cleaning utensils like putty knife, toothbrush, rags, and whatnot.
Personally, there really isn't a problem with running the engine with a can of SeaFoam (or the like) in it for a period of time (under 100 miles), then dumping it out with the oil. Most of the sludge would be removed in one fell swoop. Then when you have the heads and oil pan off, inspect and clean as necessary.
We use a pressure washer for this job. We remove the oil pan and valve covers. We then pressure wash from every angle we can reach. It makes a big mess, cover up everything you do not want to clean up later. We then reinstall the oil pan an valve covers, fill with oil, add a new oil filter. Then the engine is started and run at idle only for about 20 minutes. Then the oil and filter are changed again.
This is only done on engines that are severely sludged and would otherwise be overhauled. It can extend useful life for a short time. There is no guarantee given because this process could cause or reveal damage. We have a better than 90% success rate with the process.