I have a 2000 jaguar 4.0 s-type recently I drove my car about 10-20 miles roundtrip parked it and came out 10mins. L8tr tried to start it and it seemed strange that I had to push the pedal to start it revved it and heard a popping sound shut it down couldn't figure what was wrong so I pulled the valve covers and found out the secondary chain snapped. My question now is how can I find out if I bent a valve without removing the head I took a camera and looked at the pistons in each cylinder and they look fine I took a breaker bar and a socket and turned engine with no problem I can't check for compression because I haven't replaced secondary chain and tensioner yet any feedback thanks oh and the popping noise was the broken chain cracked a hole in the valve cover can that be repaired or should I replace that as well thanks again."Desperate for diagnosis"
A cylinder leakage test will identify a leaking valve but you'll have to turn the camshaft by hand. Normally the piston is placed at exactly top dead center on the compression stroke but that's only to make the valves closed, (and so the piston won't move down), but the position of the piston is irrelevant. You pump in compressed air through the tool which includes a regulator to limit the air to about 30 psi, then you listen four places for air hissing out.
Air at the tail pipe means a leaking exhaust valve. At the throttle body means a leaking intake valve. At the dipstick tube or oil cap means leaking rings. Bubbles in the radiator indicates a leaking head gasket or cracked head.
You do that test to each cylinder one at a time. You can expect more leakage than normal past the piston rings because the engine is cold and the piston will have likely moved down in the bore. You're only concerned with the valves. If any are bent, you'll know by the sound of the escaping air.