Jaguar XJ-S. Manual - part 26

 
 

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OIL SEAL GROOVE

OIL SLINGER GROOVE

APPLY SEALANT

SILICONE GROOVE

 

Figure 7 - Rear Main Bearing Sealing 

 

 
 

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REAR OIL SEAL -- VIN 160010 ON:  According to Phil Bates:  “In 1989, starting with engine 7P.02073, Jaguar fitted 
a new one-piece rear main bearing oil seal to replace the previous rope type.”  That 7P number refers to engines for the 
XJ12; for the XJ-S, Greg Wells says “My microfiche shows that the rope seal was used up to engine number 8S.66782 
and that the one-piece rear main seal began at engine number 8S.66783.”  Jon Jasperson quotes a Jaguar TSB saying 
this corresponds to VIN 160010. 

The TSB also calls for a new tool, JD 163, for installing or removing this new seal.  Replacement of this later type seal 
does not require removing the engine or crank, but it does require removing the transmission. 

Chad Bolles:  “No way to retrofit, already tried that, block was recast.  Crank was redesigned also.  Seal is about 5-3/8’s 
OD and 4-7/16’s ID.  Main bearing the same.” 

Unfortunately, the newer design seal seems to have its own problems.  There have been several reports of it “blowing 
out”, creating a massive oil leak.  The seal itself appears undamaged (although most people will choose to replace it 
anyway after going through the effort of removing the transmission); it apparently simply pops out of its hole.  Anyone 
with this type of seal who is working in the area -- because it blew out or for other reasons -- would be well advised to 
secure that seal.  Perhaps a Loctite retention product would help make sure it doesn’t go anywhere, or maybe it’s 
possible to add some small screws around the edge to secure it in place. 

 

PISTONS & CYLINDERS:  In general, you can buy pistons for the V12, or you can buy cylinders with pistons.  
Generally, you cannot buy cylinders alone.  Make very sure you don’t need a cylinder before you buy a piston alone.  
You cannot get pistons oversized by a few thousandths for reboring cylinders; if the cylinder is worn or damaged, it 
must be replaced.   

Fortunately, the cast iron used in the cylinders is apparently very hard and wear is usually insignificant in engines with 
less than 150,000 miles, in which case the pistons alone can be replaced.  If rebuilding, the best policy for saving 
money may be as follows:  Don’t order parts until the heads are off.  Check for a “ring ridge”, the step created about 
1/4” from the top of the cylinder by the wear from the rings.  If a ring ridge is detectable, order new cylinders with 
pistons.  If not, order pistons alone. 

The pistons and liners are available in an “A” or “B” size, which differ by a microscopic amount.  The difference is a 
result of tolerances in manufacturing, and neither is really considered an oversize for the other.  Each piston must match 
the liner it’s installed in.  There is no reason not to ensure that all cylinders within the same engine match, although 
differences probably wouldn’t be noticeable. 

The alloy piston in the V12 has a couple of steel inserts cast into the inside of the skirt.  These inserts are a thermal 
expansion control device; they not only help control how much the piston expands when hot, they also help prevent it 
from ovalizing, which most pistons normally do due to the geometry of the pin bosses.  When the engine goes from 
cold to hot, this piston design helps maintain a close tolerance between the piston and the cylinder.  This, in turn, 
reduces ring leakage, piston/cylinder wear and noise.  The fact is, these items make forged aluminum pistons look like 
lawn mower parts.  The owner seeking to replace the pistons would be hard pressed to find better ones than the 
originals. 

 

ALUMINUM CYLINDER LINERS:  Apparently aluminum cylinder liners are available for the Jaguar V12 from GKN 
Squeezeform in the UK.  Such use would require the replacement of the pistons as well, since the stock pistons are 
designed (via the use of a special alloy, as well as steel expansion-control inserts) for the expansion rate of the stock 
iron liners. 

Jeffrey Gram contacted Rob Beere Engineering, which reported:  “In the 1980’s the Jaguar Group C endurance racers 
used aluminum liners.  It is actually not pure aluminum but a compound called nickasil or similar.  This material is very 
light and is treated (don’t know with what).  In 1986-1988 the alu-liners were not used anymore for endurance races 
since the wear was too big and inferior to cast iron.  Apparently this nickasil material has a tendency to pick up material 

 
 

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by which the pick-up process is accelerated and the material wears out quickly.  The nickasil was only used on race 
engines with frequent liner renewal.” 

The V8 engine used in the XK8 and XJ8 comes with nickasil cylinders. 

 

PISTON & CYLINDER CLEARANCES:  According to Bob Tilley, “Under the Group C TWR build instructions for 
the V12, the piston to bore clearances for cylinders 1A through 5A and 1B through 5B is .0045-.005, whereas the 
clearance for piston to bore in cylinders 6A and 6B is .0055-.006.” 

These absolute values may be of little use to the normal V12 owner, since this is referring to racing engines where the 
pistons and the liners are likely to be significantly different than stock.  The implications are fairly obvious, however:  
The rearmost cylinders are more likely to develop clearance problems due to poor cooling.  There is no history of 
problems in the street application, but the information is included here for those who might make use of it.  Perhaps the 
anal-retentive might choose to measure the clearances in their piston/liner sets and put the largest clearances at the back. 

 

PISTON RING END GAPS:  Technical Service Bulletin 12-33 is a correction to the piston ring end gap specs given in 
the ROM.  It says, “Insert the correct piston ring end gap specifications into the XJS Repair Manual, sections 12.17.10, 
12.25.26, 12.41.05 and the Piston Ring Data in section 05 (Engine Tuning and Data).”  Well, it’s already off to a bad 
start; 12.25.26 doesn’t exist at all (at least not in the ©1975 ROM), 12.41.05 doesn’t mention the end gap spec, and 
12.17.10 refers to Section 05 -- which is an incorrect reference in both the ROM and the TSB, those specs are in section 
04!   

Which page in Section 04?  Another good question.  These pages are printed sideways, evidently copied from some 
other document.  When you get to the bottom of the left column of page 04-5, proceed to the top of the left column on 
page 04-6.  When you reach the bottom of that column, proceed to the top of the right column on page 04-5, and then 
proceed directly downward through the right column on page 04-6.  It will be helpful to mark arrows on these pages to 
remember this. 

The piston ring specs start at the bottom of the left column on page 04-6 and continue at the top of the right column on 
page 04-5.  The gaps in question are actually near the top of the right column on page 04-5.  Revise as follows:  The 
spec end gap for the top ring should be 0.016”-0.021”, and the spec end gap for the second ring should be 0.016”-
0.026”.  The spec for the oil ring is not mentioned in this TSB. 

 

TOTAL SEAL PISTON RINGS:  Total Seal, Inc., makes a type of piston ring set in which the second ring is a two-
piece ring.  Effectively, it puts two rings in a single groove with the gaps staggered -- so gases cannot pass either gap.  
As a normal ring wears, the gap gets larger and the leakage increases accordingly.  With Total Seal rings, the gap is 
covered by the second ring, so it won’t leak no matter how much it wears. 

Apparently, these rings are highly recommended by just about everyone who has ever used them -- including high 
percentages of competitors in several types of racing.  Testing shows considerably less leakage even compared to new 
conventional rings.  Not only will performance improve, but the reduced blowby should result in less contamination of 
the oil. 

 

SEALING LINERS TO BLOCK:  The liners (cylinders) are slid into openings in the block, and the head is bolted 
down on top of them.  The upper portion of the liner is thick while the lower “skirt” is thinner, so there is a step on the 
OD where it goes from thick to thin.  The thick portion of the liner is pinched between the head gasket and the ledge in 
the block, with the thinner skirt protruding down inside a bore in the crankcase.  The head gasket seals the joint at the 
top, while the joint at the ledge at the bottom of the thick portion of the liner is sealed only with a sealant applied when 
assembling.  There is very little pressure across this joint, but it nevertheless needs to be reliably sealed since there is 
coolant above it and the crankcase below.  A sealing failure would result in coolant in the oil pan. 

 
 

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The ©1975 ROM, Section 12.41.05 step 74, says to use Hylomar when installing the liners.  However, as described in 
the discussion on sealing the tappet block to the head on page 70, Hylomar is not recommended by its manufacturer for 
metal-to-metal joints since it is supposed to be a gasket dressing and will not harden; it eventually oozes out of joints, 
allowing them to leak.  The ©1975 ROM recommends Hylomar for the tappet block as well, but later editions 
recommend Loctite 573 and apparently 574 or 518 will also work. 

The liner-to-block joint, like the tappet block-to-head joint, is metal-to-metal.  However, the later ROM apparently 
never changed its recommendation from Hylomar for the liner installation -- perhaps because any leaks that have 
occurred were not obvious and didn’t result in complaints, or perhaps because the liner-to-block joint is a much higher 
compressive stress joint than the tappet block joint and therefore may be expected to seal reasonably well regardless of 
sealant -- the iron liner will just dig into the soft aluminum block.  Regardless, Loctite 573, 574, or 518 should be a 
much better choice than Hylomar for sealing the liner-to-block joint.  Even better:  Based on the tech guidelines at 

http://www.loctite.com

, the substance this author would choose to seal liners into the block would be Loctite 510 due 

to its higher temperature rating. 

Joe Bialy points out that the application guidelines for 600-series Loctite products may be confusing.  “The Locktite 
book specifically states that the 638 family of compounds (603, 620, 638, 641, 648, and 660) will "retain cylinder 
liners".”  The Jaguar V12 liners are “cylinder liners”, but 600-series Loctite products should not be used here.  600-
series Loctite products are intended to retain the type of cylinder liners that are pressed into bores in a block.  The 
Jaguar V12 liners are not pressed into bores; they are slip-fit into openings and securely held in place by the head.  
Retention is not an issue; the only necessity is sealing -- which calls for the 500-series products. 

Just in case it isn’t clear enough in the ROM:  The sealant on the liner-to-block joint should be applied only under the 
step on the liner or on top of the ledge in the block, not down the sides of the liner or on the inside diameter of the bore 
in the block. 

 

Performance Upgrades 

 

COMBUSTION CHAMBER MODIFICATIONS:  With an advanced combustion chamber design, the H.E. engine has 
11.5:1 compression and runs on 89 octane unleaded (Unleaded Plus).  Almost any mods to the engine internals would 
endanger the integrity of this design, and the owner would risk having to lower the compression radically and/or face 
buying octane boosters ($$$).  His fuel economy would get worse, and if he didn’t do his job right his performance 
would get worse, too. 

One modification possibly worth considering is to install the European pistons, raising the compression to 12.5:1.  
According to Chad Bolles, the only difference in the engine is the piston, which has a slightly different pin bore 
location.  This change will obviously require higher octane fuel.  The European XJ-S H.E. reportedly produces about 
30 more HP than the US version, but much of this is probably in the lack of catalytic convertors and other emission 
considerations; Mike Morrin says, “I would estimate that the extra CR alone is worth 5-8HP.” 

 

ENGINE ENLARGEMENT:  There are two ways to get more power out of an engine: tune it to obtain more 
horsepower per liter, and enlargement to provide more liters.  Of the two, enlargement has some definite advantages: if 
the horsepower per liter is not changed significantly, the durability may not suffer; the “manners” of the engine, 
important in street applications, may remain as stock or even improve; fuel economy may remain nearly unchanged; 
and the use of higher octane fuel or octane boosters may not be necessary. 

Indications are that the Jaguar V12 has a lot of room for expansion.  A 5.3 liter (90mm bore x 70mm stroke) for two 
decades, it was enlarged by Jaguar in the early 90’s to 6.0 liter (90mm bore x 78mm stroke).  AJ6 Engineering (see 
page 710) once offered engines bored and stroked in sizes up to 7.1 liter and 405 BHP. 

The room for expanding the bore seems to be limited to around 98mm.  The stroke, however, can go a long way, and 
since it is so over-square to begin with, getting too under-square is not a problem.  Bill White (see page 718) has 
prepared a Jaguar V12 for use in a 3/4-scale replica of a Spitfire fighter plane.  He expanded the bore and stroke to