I know some of our members refer to the Velo check valve as a bodge, but as someone who has owed three Velos ('53 MAC, '66MSS, and '59 Venom) they all had check valves and they all worked. That is, they slowed down or stopped wet-sumping. The spring is a tiny conical thing, and is extremely light. A wisp of a thing. From my point of view, another thing that makes the Velo ball valve different is that it is mounted in a housing directly under the oil tank. Not an aftermarket part mounted downstream in an oil line. I have never heard of one sticking shut and destroying an engine. The biggest problem with them is they don't hold the oil. A Nitrile covered ball is one of the mods people do to Velos. Never tried one. And yes, you have to make sure that your oil lines are very tight and have no air leaks. All of the Nortons I've owned wet-sump a bit - even my MKIII. Never been a problem. I've heard "stories" of wet-sumping causing anything from bent rods (!) to blown out drive side seals. But, never first hand stories! The worst I've done is a little minor fogging for mosquitoes.