reaming and cleaning old deposits.
In the 70's and 80 's I rebuilt 350 SB chevys for a race team sponsored by Kralintor Filters, employed there for 10 years. One the things about build up of carbon and other related substances in the combustion chamber and valves, is that the build up acts as an insulator. Slow to heat up but gets hot and stays very hot. Some studies show that the carbon build up can be the hottest point in the chamber,piston crown, or exhaust valve. In gassers, this would cause pre-detonation . Hot spots can only cool down, via the new air fuel mixture on intake stroke, and or via the conduction of the heat via the head to water jacket. I'm thinking that these hots spots possibly may lead to cracking of the head, best guess me thinks,,
In the case of my # 14 head with 350,000 km on it and no previous maintenance records form previous owner , to do it might be a form of insurance, and I will know for sure that it is clean, and I just love working on that old tank of a car. ps I know very little about diesels but with help I'm learning. pss just picked up a spare head #14,,now I can practice changing parts.