3.12 - XK Engine Build Information ( Terry Handley,
April 16, 2002
Really fitting HD8's to a B type head is not going to do anything to enhance
performance unless a host of other things are to be done, modifications need
to be compatible, go hand in hand to get any benefit, also more power costs
more $ per mile. An easy and economical upgrade for a Mk9 is to fit a 4.2
engine & Type 12 auto from an XJ6, these engines when rebuilt offer much
more grunt & they cost so much less to o/haul then a 3.8, the 4.2 fitted
with B Type head + 2 x HD6's go fine and are extremely torquey, the extra
torque allows a taller diff to be used with no compromise in acceleration or
economy plus the car with taller diff is much quieter than a std. 3.8 MK9.
Good B Type heads are becoming hard to find, look at the forgotten 2.4
engines as a source,it need to be taken out a little in the ports but
generally they are in better cond then B type heads from 3.4,3.8, engines,
sO many S/Port heads around & cheap.
It's 3 x HD6's or similar 13/4" SU's that will suffice for 350 +hp.
2 x HD6's will suffice on either a modified B type or S/Port head different
camshafts, better exhaust, modified inlet manifold, etc. enough flow for
maximum of about 260 real HP.
Only in the high rev range will there be any performance gain from fitting 2
x HD8's in place of HD6's and then it's marginal and not really measurable
by a stop watch, I suppose the larger 2" SU's look more tough, give more
I can't recommend any upgrade needles for HD6's with pancake air cleaners
firstly the filters differ in flow/resistance from make to make & also the
size of the Pancake Filters .
Really the MK9 filter works fine, however I realise why you wish to fit more
Sporty looking Filters.
I do have some old notes on needles that worked for me with std. XK
engine, pancake filters, B /type head etc, memory tells me they were what
suggested for the paper element or the XK ,3.4, 3.8 with the std. pancake
filters I will dig around on Monday for you, there would be some listers
that can suggest what has worked for them, I see SM needles have been
The adv. curve needs to be changed for pancake filters, see suggestions from
Jaguar/Lucas distributors, there is dist. specs in the older W/Shop manuals.
Treat the recommendations for Adv. Curves as a starting point only as new un
leaded fuels require some additional fiddling to get it all right, good idea
to use the highest octane fuel you can find, the higher octane un leaded
gives better economy so the few cents more at purchase is rewarded with
more MPG and usually better starting, smoother idle and more power.
Many people are finding after stripping engines that have been run for a
time on un leaded that their has been Detonation happening . scuffing of
piston skirts is often caused by detonation, broken rings, mouse eaten
piston crowns, worse holes in pistons. Detonation is a silent killer and
it's happening more often since un leaded introduction.
What's been required of late is to give more piston to cylinder clearance
and up the running temp of engines this necessitates also a higher poundage
radiator or header tank cap, the radiator needs to be able to cope with
extra poundage cap all new alloy radiators will cope.
Un leaded works better with engines that run at higher temp. then as for
std. XK engines, this sounds counter productive but in real time & for road
Early XK engines had differently made Alloy pistons and the alloy was of a
different mix, modern high silicon content low expansion pistons are fine
for most engines but with the XK engine despite newer composition pistons
being of a low expansion alloy etc. the pistons need more clearance this is
partly because the cam grinding of the pistons made to day is different.
Without going into the different pistons makes and designs of pistons used
in all the XK engines in real time they all mostly needed different
clearances then suggested in Jag W/Shop manuals, there was technical service
bulletins and news letters, telex's getting about many years ago with some
alarming at time advise as to piston clearances for some XK engines.
The biggest most common stuff up was & still is, people fit 3.8 Powermax
Pistons with 9-1 Compression in place of the std. 8-1 Compression piston
made by Brico, the results are not so nice with the skirts being damaged by
too tight a fit, not enough clearance.
Example of the mishaps happening now ,4.2 pistons are often given too little
clearance for the conditions the engine is to endure, also the engine blocks
are rusted in places that can not be attended to unless the cylinder sleeves
are removed, the said rust causes hot spots and too little clearance makes
matters worse, there is often then partial seizing and the engine is spoilt.
( no amount of hot tubbing will remove the said rust)
W/shop manuals and reco engine shop books have piston clearance for 4.2
engines as .0015",many give .002" ideal/preferred by me is .003".
Std XK engines from factory could have graded pistons & bore sizes varying
from std. to F to K =.005" to +.010" so each bore in an XK engine needs to
be measured and after hone a suitable piston used, problem is that only std.
sizes are now available, that is std. to .030" some .040" for 4.2, but then
with the latter one has a severe H/gasket overhang problem, all overhang is
severe but with the larger bore sizes the problem gets worse.(copper
h/gakets finished by hand is a good move)
3.8 engines are to be looked at very carefully, the new pistons around are
often 30 years old & they have gone off sitting on the shelf, a fired piston
from 30 years or more ago will retain it's shape & size much better then
some of the
said old but new pistons, furthermore as for the 4.2 engine blocks the 3.8
engine blocks rust inside & between the sleeves, one must do some careful
appraisal of the new 3.8 pistons to be used, then give as rule of thumb
extra piston to bore clearance how much more is dependant on a few things
but generally it's .002" more then recommended.
When one has the sleeves removed from either the 3.8 or 4.2 engine block and
new sleeves are fitted, pressed home to a machined stop at botton of
prepared, honed to size engine block cylinder, a torque plate is used for
boring/honing & the main bearing caps fitted & torqued then one could run
tighter clearances. ( by stepping the cylinder block & pressing the new
sleeve home ,the sleeve can not move down & away from the top of the block)
Jaguar never stepped the cylinder block, if they had some XK engine
problems would have been fewer, Jaguar however went to great lengths to
have fit the sleeve parallel with a good interference fit, this can not be
done as easy to day , cylinder sleeves now have too rough a texture on
outside of sleeve, like a big thread all the way up the outside of the
sleeve, this means that the sleeve only locates on the highs, engine shops
then use gunk to seal off, stick the sleeves, the latter does not give a
good heat sink & also the sleeve is prone to move down, settle and the
latter allows for the head gasket to leak.
Furthermore, Engine shops do not hone the block to size to receive the new
sleeve, they generally use an off tool finish, this with the said new
sleeves makes for a bad fit that with the gunk used causes hot spots.
The best engines cost more but it's worth doing the job properly, have the
new sleeves ground on a centreless grinder to give a smooth surface finish
, have the engine block honed to correct size to enable a true parallel
interference fit, step the block, use a B or C section sleeve ( this gives a
stand alone seal onto the h/gasket, C is better) flanged sleeves take lot's
of extra work to fit properly and mostly they don't get fitted properly, one
can not see how they are fitted because the flange hides it, I don't like
There are some excellent forged pistons for XK engines, they do not have to
be for race work and can be as low a 8-1 compression, Venolia make nice
pistons and they will give you the compression you ask for, 8.7-1
compression is Maximum I will now use for XK engined road cars, always take
into account the amount of metal that has been removed from head & or engine
block, use 8.1-1 and you will be safe.( Forged Piston to bore clearances are
not mentioned in this Post)
When extra piston clearance is given depending upon the make & type of
piston rings mostly std. recommended ring end gap must be adhered to, I use
file finish compression rings in all top line engines, this insures better
compression & better longer engine life.
Oil control is made easier by multi segment oil control rings, Noah's cast
iron one piece oil rings can not cope with the oil control job within an XK
I like to use a Single Moly top Comp Ring, not a Chrome ring, 2nd ring I
like a plain cast iron ring.
For engine with doubtful bores I like to use a barrel shaped Ductile Iron
Top Ring & a square face torsional, cast iron 2nd ring, multi segment oil
I don't ever now use the gapless type compression ring as it's a nonsense as
static blow by has no affect on real time engine operation, the ordinary
torsional ring with square face is fine for good bores. (gapless rings are
when used, fitted to second ring land only)
There are many types of piston rings & it can be a confusing job to select
the type of ring to use, best known brands are the safest bet, Hastings,
ACL, are just 2 I like to use, in OZ there are probably more piston ring
types made by OZ, ACL that suit Jaguars then any other maker, the ring is
selected by bore size and piston ring land sizes. 4.2 engines are lucky as
they have a bore size the same as Holden inline 6 cylinder & the 253 V/8,
makes excellent piston rings for these engines as the said GM engines are
used for many Race Cars, such as HQ classes ACL makes File finish rings
suitable for 4.2 XK engines, also have good variety of rings suitable for
ACL does not make a good fitting h/gasket for 4.2 engines it fit's badly
Payen Gaskets, overhangs into the cylinder causing firstly hot spots, then
the dam things come apart & leak.(overhanging gaskets can cause detonation)
at least the fire ring cracks & the gasket blows & or leaks.
Payen have now identified that my complaint for the last 30 years is factual
they are currently looking into a new or modified gasket, believe it when I
see the gasket.
Well we are a ways from HD8's but one thing leads to another and there is
plenty more that can be discussed about XK engines on this great list.
I have hoped for many years that there would eventually be some excellent
quality engine parts available for XK engines that enhanced longevity &
performance but after many years we still have inferior h/gaskets for 4.2
engines. There is one good thing that is often sadly overlooked that is the
US made Gran Turismo Oil Pump, the said is about the best thing one could
ever use in an XK engine. Saddens me that in 2002 there is still not a
proper fitting composite h/gasket for 4.2 engines
There has/is been some rubbish parts dished out for XK engines & many
unfortunate recipient XK engines never have a chance to show their true
potential, engine shops & Jag repair shops mostly just keep on using crap
with the mentality of it's just an old Jag or worse the thing will never be
driven very hard.
One can make a good serviceable engine from a pile of s/hand parts it's just
care & fit that make the engine work but realistically an engine assembled
with good components is going to be a much better thing, where to get the
good bit's is still the problem it was 30 years ago, pity that after all
this time that atleast one could have 25% of what's available for say a
given Ford engine, guess it's that Jag owners are not too fussy or they
don't really know too much about engines.
There is enough XK engines being played with around the world to
substantiate investment by component makers but there is still not enough
good gear, good quality parts being made, Rob Beere is one person who knows
only too well what I'm saying, he does good work and hunts around to get
things made to enhance reliability within the XK engine T/chain Dampers made
for last few years are generally crap, Rob realised this and now gets them
made to his exacting specs, however it's a tough job to get better things
made for XK engines if people don't get wise & it's a near impossible task
if there is no push from Jag owners.
3.12.1 - Fitting a 4.2 Engine in a MK2 or S-type ( Terry Handley,
November 25, 2003
"Fitting a 4.2 engine to a Mk2 and or an S Type makes some sense,
firstly 4.2 engines cost less to overhaul and because of the vast amounts of 4.2
engines made there is a lot in wreckers, breakers and even in Jag Lovers back
yards to choose from, some model 4.2's are better then others and the
differences between different models are vast, at the end of the day they are all
good enough for all but the fastest race cars, then there is some things in
favour of just a couple of engine blocks & it's not the short stud
Whichever 4.2 engine is chosen to fit to a Mk2 there is only a few
differences that can make fitting to a MK2 from very easy to a little
tricky, the only real snags are the Generator Mount, alignment of the
Pulleys for w/pump, harmonic balancer, always use the 4.2 Harmonic
Balancer and figure out the alignment problems, the 3.8 balancer is not good
enough even for a 3.8.
If one takes a 4.2 Harmonic Balancer & Split Cone to say Ross Balancers
in Sydney they should be able to quickly mod a Balancer from another
engine, the Australian Designed and made Cyco Industries marketed as a B&M
works fine but is now too expensive as it goes from OZ to the US and comes
back here too expensive, there maybe some stocks in OZ but generally too
greedy stockists bung to days prices onto it even though it has been sitting
around for a few years.
The one thing to keep in mind is the early 4.2 as fitted to the 420
sedan & Mk10 4.2,ser 1 E Type has the larger casting for the water pump but
retains the same size w/pump impeller, the advantage is the larger dia intake.
I have built many 4.2 engines with the 3.8 pump and timing cover, 420
timing covers will fit, same pump impeller size as a 3.8 , see my cooling
The B type 3.8 cylinder head can be fitted to any 4.2 engine, when
fitting to the later 4.2 engine blocks the 2 water ways at the back of the
engine block need to be tapped out and plugs made from threaded bar or bolts
screwed in by a slot hack sawed ontop, use a loctite product, if ever
theyneed to be removed a small amount of heat in that area softens the
A B Type head with the ports taken out and metal removed from under
the valve seats works very well, but good B Type Heads are getting hard to
find, don't discount a 2.4 head it is usually in better condition then a 3.8
and there are many sitting around on 2.4 engines digarded many years ago,
only the ports need to be taken out or run it as is for torque like a Mack
A S/Port Cylinder head from the many jag model sources can be fitted to
any 4.2 engine.
For most uses the 420 or XJ6 engine inlet manifold is easiest ,a 240,
XJ6 Ser 1, 420 , 2 x 2" SU's work well enough for all but the Cars that
owners are looking for the mostest, a good 2 x 2" SU set up can beat an
ordinary 3 x 2" SU set up.
Proper porting of the 2 X SU Manifold can flow more then enough.
One little snag that's found out often at the last hour of the
conversion is the Water Outlet from any S/Port Inlet Manifold does not match up to
the MK2 radiator,when one looks at the problem it can be sorted out relatively
The down side of fitting the 3 x SU's to a RHD MK2 is many, one has
to overcome the fact that the Clutch & Brake M/Cylinders are right in way
of the Inlet Air Cleaner, that is a Filter system needs to be used and the
rear most carby is so close to the Clutch M/cylinder.
The other major problem is the inner guard needs to be modified to get
the needed clearance to fit a proper effective air cleaning system.
The beating cutting of the inner guard area causes warping of the
mudguard unless real care, expertise is used. the gap between the bonnet and
the guard becomes greater as it's pulled down once the inner area is
played with, it's usually bent down bad enough from years of mechanics leaning
over top of the mudguard.
Use the 420 Air Filter assembly it works well enough, there is nothing
to be gained but noise using anything else.
One can duct cold air through the N/S inner guard and hook it upto the
420 air filter, early Mk2's had the hole there for the fitting of a Tube to
the under N/S Air Filter that was used on some export models, many MK1's
had the said, make sure you continue the pick up to a position up front rather
then just picking up air from under the mudguard.
You can see the proud area of the inner guard where the connection was
made, it was blocked by Jaguar on some early model MK2's & then later
pressings, the hole was not included.
Obviously I have only touched on the surface of fitting a 4.2 engine
and the possibilities are numerous many listers have done and are doing this
I have found that a well prepared, slightly modded 4.2 engine with 2 x
2" will still to day surprise many a modern car driver, recently I had
the occasion to let loose a Slightly modded 4.2 MK2, it was only the aged
tyres that made me back off & let an XR8 Ford Falcon go buy.
Make no mistake a modded MK2 4.2 is still today a very fast car that
can embarrass even GM & Fords supposed Quick Road Cars, you can see this
when Normie turns up at Oran Park with Holden.
A 3.8 engine needs to be modded a lot to perform as well as even a
standard 4.2 engine performs in a MK2, the extra torque of the 4.2 means a lot
more grunt without the down changes, quicker acceleration more power up the
hills, near forget 1st gear.
A 4.2 engine with a safe low compression of 8-1 goes harder then a 3.8
with 9-1 + Compression and it will run nicely on lower grade fuels.
A lightened Steel Flywheel & a 9.5" Clutch on a 4.2 livens the engine
considerably without affecting tractability.
The later XJ6 Engines are heavier then the early 3.8 engines and the
extra weight can be felt at kerb speed, however the standard MK2 Springs are
really too light for even a standard 3.8 engine so an update to at least
1000lb Front springs is needed for a MK2 that does other then sit around.
In a Racing MK2 you need 1600 lb front springs, I like 1200 lb front
springs for my road Mk2's and use a Front Anti say Bar from a 420, a heavier
bar gives too much understeer for a road car, that is unless some other
thingsare not done to make the MK steer & handle better.
A MK2 with heavier springs suprisingly does not ride too hard, most
new sporty cars with the low profile tyres ride more harshly then a modded
Obviously there are many aspects of a 4.2 engine conversion that can
be talked about on the List but simplicity for most is the key to a good
reliable fast MK2, often lot's of money can be saved by buying
scrapped 4.2 engines and pulling them down and building one nice engine.
Mod the head & inlet manifold, fit the exhaust headers that allow the
fitting of 2" od primary pipes some Headers are not large enough inside
to realise the benefit of the said primary pipes.
Avoid fitting Tube Type Headers with larger then 13/4" OD Primary pipes
you will gain nothing but heat and lose plenty of power, biggest is not
One can use the standard MK2 exhaust and a 4.2 engine , still gives
more useable power then the 3.8. Don't believe the myths about a 3.8
engines being faster, those early 3.8 E Types when compared to later
Ser 1 4.2 E Types had gearing advantages and lighter flywheels the
4.2 engines usually had the heavier flywheel.
Bring the primary pipes into one 2.5" pipe from about central position
of the g/box through to a Walker or Lukey Free Flowing 2.5 in & out
muffler and on the outlet siamese to 2 x 17/8" Tail Pipes, this set up
gives a nice note and flows enough & better then a standard MK2
twin system and it's not too noisy.