I just pulled the head off my 1994 XJ6 because of a leaking head gasket (I was getting combustion pressure in the cooling system) and after I got it off I took it to a local machine shop where they checked the cylinder head with a straight edge. They found that they could put a 0.010 inch feeler gauge under the center of the head when the feeler gauge was sitting end to end on the head. They looked up in a manual somewhere the limits of how much could come off the head and the new thickness of the head.

They said when new, the height of the cylinder head was 5.016 and the limit of what it can be cut is 5.006. One end of my cylinder head is 5.010 and the other end is 5.012 so at some point in the past it must have been surfaced once already.
Even if the cylinder was thick enough to be cut I am concerned about the cam journals on the top of the head being aligned.

Does anyone have experience with these limits of how much a head can be resurfaced and if they are surfaced, what about the alignment of the cam journals?

 

You must also realize that the cams need to be STRAIGHT.
You may 'skim' the bottom, but the cams may be 'bent' when they are installed and torqued down.

The only machine shop that I used years ago understood LONG cylinder heads and the need to get them in tolerance before 'skimming' the bottom surface.

They used a large oven and bolted the head to a massive steel plate to heat and straighten the head to within a few thou of straight.

Sometimes it took a few tries but they always got it done.

I guess you could just find a cam set with a 'U'joint in the middle??

bob

 

Yes, I understand the cam journals are on the top of the head and need to be aligned.
This is why in my post I said "Even if the cylinder was thick enough to be cut I am concerned about the cam journals on the top of the head being aligned."

Where was this head straightening machine shop at and are they still in business and able to do this again?

 

The name of the shop was ACCURATE ENGINE in Fort Worth TX.
The owner started in the early 70s and sold all the shop equipment a few years ago when he retired.

I used his shop for 30 years. He was not fond of the Jaguar engines (a lot of work) but he was good at them.

There is a point at which the warping becomes significant enough but I don't know the tolerance for the cam alignment.
You might be OK with the amount you have?

bob

 

Tomorrow I am going to contact the machine shop to see if they have a way to measure the alignment of the cam journals.
I am also searching for a replacement cylinder head or core engine.

 

I feel compelled to comment. Bearing in mind I have 1 count em One head job under my belt (it was successful) you didn't mention- was your head gasket good when you removed the head? I say good as in no blown out areas, not good as in re-useable. And if it was then I must assume that your warpage was really to blame. In any case, would a new set of head bolts be enough to pull the head back to flat once they are properly torqued ? The bolts do after stretch somewhat - as I understand it. Just food for thought. Hoping maybe you have a somewhat easier way out... good luck.

 

There was one section of the gasket around number three cylinder that was discolored brown on the underside of the gasket and I am fairly certain this was where the gasket had failed and was allowing combustion pressure and gases into the cooling system. There was a slightly less obvious place in a similar location on cylinder number four. See photos below.


brown discoloration on block around cylinder number three


Similar discoloration on bottom of head gasket around cylinder three sealing surface.

 

Disassembling FLAT head
Just a FYI to this thread. Over the past two days I managed to find and remove a cylinder head from a 1993 XJ6 in a local junk yard (the place where they broke the intake manifold up to get the starter out for a previous customer)
This head after being checked by a local machine shop that I trust, turns out to actually be flat. With the straight edge test, it had less than 0.002 clearance at the center of the head which is different than the two previous heads I had checked that had 0.010 - 0.012 clearance at the center of the head when checked with a straight edge.