Here are some pictures showing how a home-made device can be used to easily separate V12 heads from the block.
Having studied Kirby Palm's excellent technical summary of the V12 (downloadable for FREE from http://www.jag-lovers.org/xj-s/book/XJS_help.pdf), and having listened to some tales of woe from others who have struggled vainly to separate the heads from the block, I decided it would be well-worthwhile making up a device to simplify head removal - particularly as I have at least two engines to rebuild. Also, when I went to collect this engine, I was shown a block where one head had been completely removed and the second was stuck fast - even though there was 3 inches of fresh air between the head and the block. The owner had tried over many months to separate the second head (without the benefit of "The Beast" but all attempts had failed. He was even considering having a hollow reamer made that he could slip around each stud - but I suspect this is "clutching at straws". Perhaps, if I am feeling generous, I may pay him a visit with "The Beast" in tow.
I have probably spent more time making up such a device than actually working on the engine, I feel it was time well-spent! I have christened the head-removal device "The Beast" because of its size and weight :)
I must add here that I have become an avid reader of the V12 forum on the "Jag-Lovers" website. Over the last few weeks I have learnt much about the V12 from its contributors - many of whom are very experienced in Jaguars in general and the V12 in particular. I unhesitatingly recommend you subscribe to this forum if you are contemplating a V12 rebuild - the members there are invariably helpful and willing to pass on the benefit of their experience. You can visit Jag Lovers by clicking HERE.
The "flat-head" V12 in the photos had been stored in various garages/lock-ups for the past 20 years or so. I was told it was removed from a XJ12 saloon. Because of its history, I was anticipating difficulty in persuading the heads to leave the block .... The first thing to greet me when I came to remove the head nuts was just how many there are! Having been used to the relative simplicity of the XK 6-cylinder iron block, it seems I will have to develop the patience that is needed for "12 of everything" .. or should that read "24++ of everything"? Of course, it is important to remember to remove ALL the nuts holding the head down - including the ones attaching the head to the top of the timing-case. "The Beast" is more than capable of pulling a stud out of an alloy head if a nut is left attached.
Incidentally, I discovered that there is no need to make up a special tool to hold the camshaft sprockets in place during head removal if you happen to have a couple of suitable external circlips. I found that by placing circlips into the grooves already machined into the end of the sprocket spindles, the spindles can simply be dropped over their respective retainers. There is also no need to slacken the chain using special tools if you simply fasten one of the sprockets to its holder so it remains out of the way while the head is removed.
"The Beast" is fabricated from two sturdy 3/4" steel plates. The top plate fits over a series of threaded bars that are welded into the bottom plate.
Step One - attach lower plate.
Place the lower plate on the head so that the camshaft locating studs protrude through it. It can then be fastened down using the original nuts and washers. Please bear in mind that this is an alloy head and do not over-tighten these nuts!
As can be seen in the next photo, the studs at the front of the engine are in different places left to right. I don't know if this is a peculiarity of all these V12 engines? The plate covers all the camshaft studs on the left-hand head, but misses the front pair on the right-hand head. If I was to make another bottom-plate, I would add extra length and holes to accommodate this left-to-right difference..
Step Two - add steel rods
Drop the rods (I used stainless) through the bottom plate so that each rests on a cylinder head stud. The diameter of the rods is slightly smaller than the cylinder head studs and they are chamfered to facilitate them following the studs through the head.
Step Three - place upper plate
Place the upper plate over the threaded bars and, using the small socket-head screws, level it making sure all the stainless rods are in contact at both ends.
Step Four - fasten upper plate
Check the plates are parallel to each other and fasten using long nuts/washers on the threaded bars.
Step Five - remove the head.
Remove the head by tightening each double-nut the same number of turns, in rotation around the upper plate. The whole operation took under an hour for each head and required very little effort - in fact, it was quite therapeutic and satisfying to see the head gradually slide up past the studs. The hardest part (once the head was lifted almost clear of the studs) was lifting the head complete with "The Beast" off the engine.
I could be persuaded to loan "The Beast" out when I am finished with it in return for a small donation towards its fabrication costs.