what causes bent valves and how do you know if they are bent?
 

What causes valves to bend? Mis-shifts, hitting rev limiter, p to v???

How can you tell w/o pulling heads (if their is a way to check)

everything you mentioned causes the valves to bend...you can't "check" without pulling heads...but it won't run well with bent valves

Do a compression test on it.

Not compression; a leakdown test.

typically, the valves aren't bent its the pushrods. To check those is easy and you don't have to pull the heads. They usually bend when the engine is overreved and the valves float. When the spring finally pushes the valve back, the cam lobe is coming up again and the pushrod gets slammed.

valves bend when piston hits valve

Bent valves don't usually spin freely in the guide. You can feel this when you lap them in. You could remove the rocker and probably feel it from top side also. The compression test or leakdown test will confirm.

did you have any bent pushrods? I had a few bent ones and the damage went even deeper into some bent valves as well and a very loose timing chain....

Causes:
-not enuff spring pressure
-not enuff piston to valve clearance
-break a timing chain

Like said it is best to perform a leakdown on the cylinders to confirm if you have a valve problem. This test can confirm a good cylinder or a bad one & where the cylinder's seal is compromised.