I used to work with Fairbanks Morse opposed piston 38D's back in my mispent yute. Marine applications. I think they were 12 cyl. OP 2,000 shp.
When we got them new we were instructed to open the vent cock in the cylinder wall and roll the engines over a couple of times to make sure the cylinders were clear. Then close them up, reset the fuel rack and give it air and away we go. Problem was, when you rolled the engines prior to start, the oily mist would get all over the engine room. After about three months, we just rolled them over a few turns(closed) and started them up. Of course, you always first checked lube oil and coolant in the expansion tank, which was well above the engine top. We always kept the compressed air tanks charged (at 200psi iirc). And the very first thing you did before going to the engines was blow the air tanks clear of water.
We ran them at 900 rpm full speed. I think idle was about 150. Been a long time.
We never had any problem starting them. A few cranks (compressed air) and the'd fire up. Good engines. They're still in service after 30+ years.
http://www.tugboatenthusiastsociety.org/Pages/tugmach-diesel-modern-FM.htm