You put enough spring load on a valve and it will seal. Absolute fact.
Had a customer bring in his heads for a freshen up. So I pulled a vacuum on them and they were sealed right up.
When I took them apart, every intake was bent so bad you could set the valve on the bench and see the crooked stems. 5 exhaust valves were bent, but not that bad. All sealed up.
I had him pull the short block and bring it in. He was a home assembler. He didn't have the cam times correctly AND he didn't measure piston to valve clearance. And that's what you get.
So you can have a bent valve and have it seal. Seen it so many times I can't count it. So the solvent test, pulling vacuum on the port or using a flash light in the port only tells you it's sealed. Nothing else.
