Regarding crosshead bearing failure, I have read that at slow speed it is difficult to establish a lubricating film because there is an imbalance between forces due to combustion and forces due to inertia. This information is from a maker of big low speed two stroke engines used for the propulsion of ships.
I don't quite understand the explanation. How are these forces imbalanced and how does this contribute to eventual failure of the bearing?
The crosshead bearing slides within a track and connects to the conrod and then to the crankshaft. In a vertically oriented engine the pressure on the bearing is always downwards, resulting in a depleted lubrication film on the lower contact surfaces of the bearing shell.
To supply lubricant to the entire bearing, high pressure oil is injected into the bearing and distributed by a pattern of channels to guide the oil uniformly.
Oil pressures can be as high as 20bar in some designs.
This article (search "crosshead bearings") provides a good introduction to the topic Operational Information, Crosshead Lubrication
