Jaguar Repair: 1989 Jaguar XJS V12, jaguar xjs v12, 1989 jaguar xjs

Question
Car overheated and shut down.  Car does still start however makes a tapping sound towards the driver side firewall.  Is this definitely indictive of a dropped valve seat and if so is a complete rebuild the only remedy? If not what else might it be and what kind of money would I expect to pay for a repair like this?  Just looking for guesstimates, I love this car but at some point it's not fiscally prudent to go forward.  Thanks in advance.

Answer
Hi Donald,
Even though I have no experience nor info on any Jaguar after the 1987 XJ-6 I can tell you that you first need to run a compression test, throttles open and turn the engine over at least 4 or 5 revolutions on each cylinder tested. Also check for CO in the cooling system.

Also be aware that the V-12 is what they call a "wet sleeve" engine meaning when each head is removed the cylinders are loose and often come up which allows trash to get under the lower cylinder seating area. This then requires that the complete engine must be torn down.
You should not let any one try to build this engine unless they have V-12 Jag experience.

I can not give you a price but unless it is a show class car the job (IF IT REALLY DOES NEED REBUILDING) will possibly exceed the value of the car.

You can't condemn the engine unless it is tested. Then you can check the price of rebuilding it or a salvage yard engine or a conversion kit from Johns Cars to put a 350 Chevy in it's place.
Howard