I think the most important thing is that oil is delivered to the end of the crankshaft.With roller bearings there is no oil pressure and while the crankshaft is rotating it sucks all the delivered oil with centrifugal force into the crank.No seal like on BSA or Norton twins is necessary.Regards Erik
You beat me to it Erik, the other bikes have plain bearings & require pressure to keep the surfaces apart. The series "A" Comet that I've hoarded for over 50 years is fitted with a homemade B/E bearing (floating bush) like Royal Enfield, I had a model "J" 350 for a short time while waiting for Alpha to fit another bearing ( three B/E in four years and rarely got more than 50k out of them)
Series "A's" have the advantage of a gear oil pump whereby the oil flow in constant supplying and scavenging more than a double start Picador pump (in his snarling beast by Roy Harper, Vincent wished he had kept it) I've altered the supply by half as much again by machining the pump housing an extra 1/16" deeper and fitting 3/16" wide gears, the scavenge is 1/4". Are any mathematicians out there to calculate the centrifugal pressure of the oil in relation to RPM.
Groove machined internally with herringbone channels nearly to the edge as didn't want to lose what little pressure there is to the inside and out surfaces which only need to travel half the surface speed of a conventional plain bearing. Vincent also went on about plain bearings RR77 in a Grey Flashes that failed on the TT bike but John Surtees went on to race his for a few seasons totalling approximately 6,ooo miles. The proof is in the eating.
bananaman