Originally Posted By: BrocLuno
OK, good on you, I should have been more specific about retained film "thickness" for journal bearings. That was me falling into the brevity trap "assuming" folks would make the mental switch between rollers and plain bearings and their requirements...
You're right about clinging to metal, Syn's will do that very well. But they are lousy at capillary fill so they do not stay in the journal bearing surfaces in as thick a film and dino oils...
I agree with you on IC engines.
I've pulled apart quite a few, and including two strokes, you end up in an oily mess.
Piston rings and pistons, and bearings hold a tremendous amount of oil through capillary action, and you are quite right, the first few seconds when oil pressure is rising, this is the sole reserve of lubricant...it's at it's absolute thickest, so will be quite effective. Also, there's the left over tribofilm for the boundary stuff.
People who talk "dry" starts clearly haven't been elbow deep in an engine.
My (well used to be my) GE derivative steam turbines aslo had electric and shaft driven oil pumps. One electric (jacking) to lift the shaft on the plain bearings (the tilting pads needed no such assistance), up to 800RPM, when the wedge takes over, and the electric aux oil pump to provide bearing oil up to 2700RPM when the shaft driven pump takes over...never pulled apart one of those (ISO32) and not had an oily mess either, but they are clearly different to IC engines.
OK, good on you, I should have been more specific about retained film "thickness" for journal bearings. That was me falling into the brevity trap "assuming" folks would make the mental switch between rollers and plain bearings and their requirements...
You're right about clinging to metal, Syn's will do that very well. But they are lousy at capillary fill so they do not stay in the journal bearing surfaces in as thick a film and dino oils...
I agree with you on IC engines.
I've pulled apart quite a few, and including two strokes, you end up in an oily mess.
Piston rings and pistons, and bearings hold a tremendous amount of oil through capillary action, and you are quite right, the first few seconds when oil pressure is rising, this is the sole reserve of lubricant...it's at it's absolute thickest, so will be quite effective. Also, there's the left over tribofilm for the boundary stuff.
People who talk "dry" starts clearly haven't been elbow deep in an engine.
My (well used to be my) GE derivative steam turbines aslo had electric and shaft driven oil pumps. One electric (jacking) to lift the shaft on the plain bearings (the tilting pads needed no such assistance), up to 800RPM, when the wedge takes over, and the electric aux oil pump to provide bearing oil up to 2700RPM when the shaft driven pump takes over...never pulled apart one of those (ISO32) and not had an oily mess either, but they are clearly different to IC engines.