We used to paint the insides of our Compressor Crankcases back in the 80's.......AFAIR we used International Paints Yacht Paint. At the time I thought it was to seal the inside of the case and to stop any 'sand' getting into the oil. The Compressors were BIG buggers that a bloke could stand inside and they were cast iron.
The Crankcases on the smaller Compressors were ALL 'fettled' meticulously and the 'Fettlers' were very proud of their skills and experience in making sure any and all loose bits/ sand were removed. We also had a huge Degreasing machine where Tricoethylene was the prime cleaning agent, and I was pally with a Painter who was known as a "Dawber' (it was an American Company) who told me 'in the past' he had had to apply filler along all the welded seams on the Air Receivers (Tanks) before painting them to make the welds look tidier !
Our Turbo Compressors Driven by a RR Avon Engine) had Lube Oil and Seal Oil Tanks (the Seal Oil was for the seals around the Compressor Shaft) and these were built into the skids which the Compressor and all their ancilliary kit was mounted on. We lost a lot of sleep over welding slag in these tanks and the lads who had to climb inside and work in confined spaces deserved a lot of praise. We didn't lose many Compressors due to their seals being buggered up on Test, but if we did, it meant a couple of days to strip the seals out and replace them and it put our Test Department under a lot of pressure as they suddenly had to work 24/7 to get their programme back on track. It was a great place to work as many of the blokes were Time Served Toolmakers or Machinists (mostly from the Altrincham area) and there was only one way to do things there - the right way !
I wouldn't be surprised at Honda Sandcast Engines having a sealing coating applied......as Honda wouldn't want any 'bits' buggering up the oilways of their biggest ever Project back in 1968/9 would they !