just bought 77 xjs

[John Vudmaska]

i just bought a 1977 xjs the motor runs but
they told me it had a blown head gasket
i have worked on many v8s but this is my first
12 cyl.
is there enough info in the haynes manuals
to guide me in replaceing head gaskets
thanks john

 

[John S Farrington]

If your head gasket is blown, you had better check the head for warpage before you proceed. The Haynes manual is a good start. The only complexity is the overhead valve cam drive system
Besst regards. Jack Farrington

 

[Michael J.]

You are about to enter the twilight zone. I just went through this, I was not so lucky though. I had a split liner. Check out the replys and questions over the last ninety days. Perhaps some of the replies that I had will help you.

Heads held on with studs are a Royal Pain to get off. I had to resort to a crowbar and a block of wood to walk the head up the studs. Use oak or plywood shims to keep the crowbar from gouging the head. Corrosion on the studs and/or radiator leak sealant glues the studs inside the head. I tried penetrating oil. It was not much help. It is a slow process.

If you have the facilities, pull the engine. It is easier to work with the engine in a stand. Pull the intake and exhaust manifolds. A bottle jack can then be placed aganst the lower block flange and push against some of the head protrusions. Not much room to do this in the car.

American V8s use bolts rather than studs. I was not prepared for the degree of trouble involved. Apparently Packards used studs also. I just saw a comment in Hemmings Motor News about how hard it was to get Packard heads off because of the studs. Patience was the key.

Because the head gasket is made from several layers of thin steel, it will be completely rotted away from the open areas. It will look pretty good where it was sandwiched between the cylinder liners and the perimeter of the block.

I did not try the rope trick suggested by several respondents to my inquiry about head removal. I don't think it would have helped considering the dried gunk on the studs and inside the hole bores on the head. I had to use a lot of force to move the head. Work it at every stud location so that you do not warp it.

It will be pretty disheartening, and very slow going. DO NOT GIVE UP you can do this!

 

[XJRpilot]

GOOD LUCK!! and i mean GOOD LUCK!!
i recently got rid of my 87 xjs that had a bad head gasket. one of the cylinder liners cracked. it was on the b bank head. too much work for me. get the factory repair manual. 100 times better than haynes. the v12 engine is complex and very expensive. it gave me a few grey hairs.
as the jag mechanic told me, " if your going to replace one head gasket you have to do the other".
"and since the heads are off you might as well rebuild them". "and you should replace the water pump as well". you see where i'm going. the cost of all the replacement valves were close to 400 bucks alone. total quote for the mechanic to do the v12: $3,900, if i did it myself:
about $2000.00 including head rebuilds locally. i bought a mgb instead, and sold the xjs to someone who can afford some gray hairs. it did run like the devil when it was perfect though. really smooth until something goes wrong. i'll stick with the 6 cyl xk engines.