Does anyone know how much pressure roughly there is inside a ZX9 sump? I've chopped and welded it and it seems to be holding oil fine sat here after patching a few pin holes but I'm wondering if it'll leak when it's on and running?

Assuming that your crankcase breathes then the pressure inside the sump should be near atmospheric.

Cool. That's good then. Just noticed 2 more tiny pinholes where it's weeping, not dripping though

Remember the oil viscosity will change when it's piping hot though!

There shouldn't be significant presure, just the weight of the oil. Once it's hot though the oil will get a lot thinner and find any gaps.

When the welding is finished on the sump, test it by filling it with Clean parafin

You'll soon see if it leaks..

and if it still leaks.... quick steel.. its fookin awsome stuff

Yep I was thinking of quick steel as I don't want to be bothered keep messing with pin holes and then creating other pin holes. It's been a good project to learn on with all the nooks, crannies and bends but it wasn't easy and I wouldn't want to do it again.
I'll try paraffin tomorrow. Thanks all.