Jaguar Repair: 1974Jaguar XJ6L series 2, oil pressure gauge, compression gauge

Question
Hello, I have a 1974 Jaguar XJ6-L series 2 there's a "knocking sound  in the engine.It only happens when starting up in the morning,then goes away once car is warmed up. What's causing this? Do I need a new engine or overhaul? As I've been told..it has 83,000 miles. One owner car. Thing is nobody wants to work on it! If I need a rebuilt engine why not repair the one I already have?  Another Jaguar engine of same vintage would probably have more miles than mine.  I'm not getting rid of it for sure!  The car has not been abused at all.  But in Los Angeles can find absolutely NO ONE to work on it.  What will stop the "Knocking in the engine and how much is a fair price to pay?

Answer
Hi Ron,
83K miles is low mileage for a Jaguar and is not normally a mileage that would need an overhaul (if the mileage is real) In the dealership I often had cars brought to me for an engine evaluation and it is not hard to do. I would not recommend that you take the car to just any mechanic to overhaul (if that were necessary) However, the tests to see if it is necessary can be done by any mechanic or even a DIY. You do need a few inexpensive tools. A compression gauge and an oil pressure gauge. First run a compression test (throttle open) You should see 140 to 180 PSI on all cylinders with little difference between cylinders. Then remove the smaller of the two oil sending units mounted on the lower right side of the block. Install the oil pressure gauge fitting in the hole and start the engine and read the oil pressure. It should read from 25 to 35 PSI at idle and 45 to 65 PSI at a fast idle (1500 RPM)
The compression test checks the combustion chamber for valve leakage. If any cylinder is low then put about a teaspoon of engine oil in that cylinder and run another test and if it is still low you have a valve leaking and if the low cylinder raises to a good pressure, you have a ring problem on that cylinder.
The oil pressure test is a test of the engine bearings. If the pressure is low or slow to come up you need to change the oil and filter and test again and if it is still low, You first need to remove the oil pressure regulator valve in the filter block and check the valve and it's spring. If they are in good condition you most likely have one or more bad bearings and the engine needs to be repaired.
There are a few other things that can make an engine knock when cold like piston slap but that and other noises need to have an experienced Jaguar mechanic listen to it to pinpoint the location and cause.
Note if the knock is there if you warm the engine up and shut it down and leave it for 15 minutes and then start it up again.
As far as cost, that totally depends on what is wrong.
Howard