Hydraulic lock
After my experience with a set of oily 3350s the way I seem to remember it was if oil seeped into the bottom cylinders then the engine would lock up on the compression stroke, as no valves open, and that is where possible damage to con rods could occur.
To try and turn the prop by hand was almost impossible given the height of the outboard engines on a Connie, so you had to turn them on the starter prior to ignition selection, and should a hyd lock occur then the starter motor had a clutch which would slip so preventing damage to con rods.
A locked engine would require you to open the cowling remove the offending cylinder spark plug and drain the oil into a bucket. It was then a good idea to turn the engine again on the starter, with the plug out, to scavenge any remaining oil from that cylinder and also to ensure you had got the correct cylinder in the first place. Button everything back and start the engine.
A messy proceedure and to overcome it happening when we were ready to go we would about 30 minutes prior to start turn the engines through 12 blades [ cautious we were] to ensure there was no lock or if there was to give us time to go through the drain proceedure.
As to starting the engines, we would go 12 blades and I would do this with fully rich selected[ to prime each cylinder with fuel ], throttle one inch open and at 12 blades ignition ON and then watch through the flight deck door for 3 and 4 engines to see how the start was going. In the case of 1 and 2 engines listen to captains calls and watch their fuel flow meters which gave a kick when the engie lit up. Then fuel and mixture fiddling with to prevent the engine going to far above idle before the oil had warmed up.
Each of the engines had their own requirements and had to be nursed and coaxed to light up, but when you got a good start on all 4 it left you with a good feeling.
Jets are so easy, sometimes
