Steve, maybe I'm misreading it but that XL150 drawing is showing the groove on the split line between rod and cap, not in the 'TDC' position.
This is one of those areas where I suggest it is wiser to follow established practice than hang your hat on a theory - fact is there aren't a lot of splash feed engines around these days and much of the original thinking (assuming it was correct to start with) is lost in the mists of time.
Bob, in answer to your earlier point, I've never used a shell big end with a groove in it (centre mains have a fat groove around the circumference centrally). Though my engine is pressure fed through the crank I'm sure others use them with splash feed. And I agree the 1 or 2 thou running clearance at the edges of the bearing should be ample to allow exit of oil (at least, if the incoming oil is under pressure - though I imagine it departs equally quickly when splash-fed while rotating at 50 or 100 times per second).
This is one of those areas where I suggest it is wiser to follow established practice than hang your hat on a theory - fact is there aren't a lot of splash feed engines around these days and much of the original thinking (assuming it was correct to start with) is lost in the mists of time.
Bob, in answer to your earlier point, I've never used a shell big end with a groove in it (centre mains have a fat groove around the circumference centrally). Though my engine is pressure fed through the crank I'm sure others use them with splash feed. And I agree the 1 or 2 thou running clearance at the edges of the bearing should be ample to allow exit of oil (at least, if the incoming oil is under pressure - though I imagine it departs equally quickly when splash-fed while rotating at 50 or 100 times per second).