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Jaguar Repair/4.2 liter head bolts


QUESTION: I am rebuilding the 4.2 liter engine in my 86 XJ6. I am replacement the head bolts but cannot find a reference regarding the pattern the specific bolts screw into the block. There are 14 bolts,of 4 different lengths. Can you please tell where each length goes?

ANSWER: Hi William,

There are two major different sizes, the long studs that go all the way to the bottom of the block and the short ones that go at the front and rear into the top of the block. There are two slightly different lengths in each. The engine lifts normally fit on the first and second studs from the front and on the second and third from the rear. Each engine lift get the longer studs. They normally came on the intake side but I have found them in different positions over the years.

If you have three slightly longer long studs and only one slightly longer short stud then they go as I just stated. If however you have two slightly longer of each then move the rear engine lift all the way to the rear. All of the studs that have the engine lift get a round washer and all the others get a "D" washer except where a plug wire organizer support went. some of them came with round washers. The nuts and washers were not chrome on the Series III cars but some people had them chromed or bought the E-type and other earlier Jag head nuts and washers.


---------- FOLLOW-UP ----------

Thanks for getting back to me. I knew it had to have an obvious answer I couldnít put my finger on.  Do I need to torque them to a spec?
Also, do you know of any upgrades I can make to the AC compressor and are there any problems converting the system to R-134? Another nice upgrade would be a 4,5 or 6 speed auto transmission I can install in the car, any sources for that?  Perhaps a serpentine belt system to replace the individual belts?
Much Appreciation,

ANSWER: Yes, you need to torque the head nuts and do it in two steps and start in the middle and work you way toward both ends.

The Harrison compressor is a poor compressor but I don't know of a bolt in replacement. I installed a Sanyo compressor but I had to make adapters to make the hoses fit and had to modify the mounts too. It was a lot of work. If I had it to do over I would have just made the mounts and had a hose company make hoses to fit the Sanyo compressor.

Why on earth would you want to put R-134 in it? as that is a very poor refrigerant and needs to be compressed much higher to work at all and even then it is a poor choice. R-12 is a better refrigerant and only poisonous when burned where R-134 is poisonous in it's natural form. A better one is "Freeze-12" which comes in other names and is a better refrigerant then either one of the Dupont products.

There may be an optional transmission at "John's Cars" in TX. They make several different adapter kits for Jags and other cars for different transmissions.

Never heard of anyone making serpentine pulleys for the Series III Jag.


---------- FOLLOW-UP ----------


Thanks again. Iíll check out the Freeze-12.

I hope you don't mind more questions.

I didn't make it clear, but my previous question concerned torqueing the head bolts, not the nuts, into the block before I install the head and torque the nuts to secure the heads. I didnít find a reference for head bolt torque specs, (as opposed to the nuts), in the shop manual. I canít imagine them not being torqued in unless they get torqued in when the nuts are tightened up.

Thanks again.

I worked for several Jaguar dealerships and rebuilt many 4.2 Jag engines and have a factory manual and I have never seen a quote on the torque of the long or short studs. I usually just double nut them and tighten them a little tighter then the torque specs. (do not use lock-tight on the studs) However, if you have removed or changed any of the long studs you need to clean out the hole and area that the stud fits into at the bottom of the block as trash can and will drop into the hole when a stud is removed. I do that with a piece of tubing inserted into the hole and use compressed air blown into the tubing to clear a hole.

Also, If you note any deterioration of an old stud close to the bottom you must discard it and replace it. It will at first look as though it is rusted away but after cleaning you will note that the metal is not rusted but just eroded. This is due to electrolysis and not rust.

You must first do a voltage drop test of the ground system (ground strap from engine to frame.) Then install an additive to the cooling system to counteract electrolysis. The only place I found it was at a diesel truck parts store.


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Howard M. Fitzcharles III


Jaguar from the XK 120 to XJ-6 ser. 3 1987


Dealership line mechanic on MG, Triumph, Jaguar for 15 years, Instructor in commercial mechanics school 2 yr. Product information manager for piston and valve manufacture, Instructor & hotline answer man for import car parts importer 15 yrs.

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