I have a 85 jaguar xj6 vaden plas with the original straight 6 cyd. rebuilt with about 10,000 miles on motor. A misfire or something caused a slightly bent intake valve on the last cylinder closest to the cab. when the motor is running I can pull the electricty from the fuel injection and can tell the difference, but a compression test shows almost no compression.( all other cyl. have normal compression) Is there a way to change that one valve without taking the head off. like maybe through the air intake manifold, if I take that off. If not what is the quickest way to accomplish this.

 

you can take the valve out without removing the head......but you have to pull the oil pan, the crank, and the rod and piston for that cylinder. then you can drop it out the bottom
you have to pull the head, but valves DO NOT bend by themselves, something had to hit it.(like the piston) or FOD

 

Removing the cylinder head is by far the easiest option for the amateur mechanic. I had a bent valve on a 1980 4.2 happen to me in 1995, and a chap I know who was an expert in these engines fixed the head and valve in about 4 hours working with a colleague. He also checked all the other valves at the same time. Engine ran perfectly afterwards and until I sold the car 7 years later.

I don't think a misfire should cause a bent valve. What can happen is infrequent use causes lack of oil at top end of the engine, so starting after a long period of storage, one should not rev engine until it's warm so the oil gets to the valves and guides.

Cylinder head might also have been skimmed too much, so the valves are much closer to the pistons than normal. Do you get any pinking at all ?