Ken: I don't know if I have ever seen the start up wear location quantified, but it may have been in some study. Certainly the rings are a wear area as they begin to move, and since they are splash lubricated, start up would be the worst time for wear. However, since start up is a no load condition, there would be less cylinder pressure trying to force the rings against the cylinder wall. However, the bearings, crankshaft, rod, and camshaft, are under higher loads than the rings and cylinder walls, and pressure lubricated, and those first few revolutions are without pressure and thus little or no
oil flow. And, usually, the
oil galleries empty back to the crankcase as the engine sits idle and must be filled on start up. Additionally, since the crankshaft bearings are normally hydrodynamically lubricated, the crank journals are just sitting on the bearings before the engine is started, and for the first few revolutions there is boundary lubrication with very little, or only a hint of
oil available for lubrication. The journal must be lifted off the bearing with an oil wedge created by the rotation and the oil pressure. The same thing applies for the camshaft to a degree, less load though, but it is higher in the engine and it takes longer for the oil to get to this area of the engine. Also, the cam lobe-lifter is all sliding friction unless a roller lifter is utilized, and there is very little oil on the cam lobe at start up, but there is valve spring pressure as soon as the engine turns and even brfore depending on where the valve is in its lift.
You are right about the Accusump not providing lubrication to the rings, but it would allow the bearings to be pre-lubed and thus minimize start up wear in those areas. While you would not impact the ring start up wear, you would on the bearings, and since the bearings are a much softer material than the rings or the cylinders, I would surmise that the wear rate would be greater at start up on the bearings than on the rings.
That is my lubrication logic for the day.
Bob, your comments and thoughts are appreciated.
Jerry