Originally Posted by LouieMCman
What's the opinions on whether the 3 speed hubs will hold up to say a 5HP motor?
Dunno, it may well be right on the edge... There was quite a bit of debate about the 3 speeds when I first decided to put a worked 66cc through a shiftkit and a Sturmey Archer X-RD3, yet roughly 3000 miles of abuse later it's still workin' as fine as the day it was new *shrug*
I'd give it a shot, newer internally shifted hubs are pretty dang tough, I suspect most of the failures were with old, beaten & neglected hubs and improper shifting techniques, "skipping" between gears due to maladjustment & "speedshifting" (not backing off the throttle while shifting - causing a "slamming" effect on the hub).
What "5HP" engine are you considering?