From what I have seen and personal experience with the old bikes I would say 3 times as long since I was doing top ends anywhere from 35,000 miles to 50,000 miles depending on filtration,maintenance,and usage. I am not and wasn't too concerned with no cam bearings,not that I like it but I do know from the automotive world they seem to last quite a while with the modern syn. oils. And replacing a head is one thing while a whole engine is quite another. So when I heard both no cam or main bearings I wasn't liking it. I have quite a few of the 50s ,60s ,and 70s Triumphs and they are nearly eternally rebuildable. I can't count the times I have rebuilt my chopper engine (in reality 5 I think)but with no mains it wouldn't be the case.
