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Swapping heads

Swapping Heads

To all, Will the head from a 3.8 -9 engine work on a 3.4 -8 MK1 block? Anyone with an opinion one way or the other may respond, especially those that may have actually done it with successful results. Aloha, Rob XK-140 FHC

Sure, Rob! I've done it, too many years ago to remember, with, first, and XK-150S head and, later, an XKE head, onto my original XK-140 3.4 liter block. You can bore out the inlet manifold to benefit from two 2" SU carbs, or fit an XKE inlet manifold set, as a later upgrade. You might have to fool with the inlet manifold porting, depending on the type of 3.8 liter head (no swseat with a sedan head) and may have to keep the tachometer output that originally came with the new head. Either set of cams will work. It's an upgrade worth doing, for inproved driveability. Is your original head a C-Type? Keep the original, for possible restoration; use the original cam covers, if they'll fit (tachometer drive may be different). Enjoy!!! Snow here last weekend! - Larry Schear, Twin Cam, Inc.

Rob, No problem. CR is determined by the piston, not the cylinder head. But it will have to be a head from a Jag that had 2 carbs for your manifold to work. - George Badger

I don't think so. I tried to switch blocks on my 120 to a later configuration but to my surprise the cylinder spacing was different, so nothing lined up. I went instead to a MK1 block which worked. - Carl, 680305 XK120FHC

Carl, If the spacing was different, it is because you were trying to use a 4,2 block which has different cylinder spacing Of course Rob can put a 3,8 head on a 3.4 block. The compression ratio is irrelevant as well as the origin of the block ( MK1,2,7 etc or XK ). George, I do not understand your reference to the number of carbs which depends on the type of inlet manifold used: If the head is a B type ( ex XK ( not 150 S ) or MK 7, 8,9, 1,2 etc ) you can only put 2 carbs ( or 3 carbs with WEBERs ! ) If it is a Straight Port type it can be fitted with a 3 carb manifold ( as XK 150 S, E type, MK 10 , 420 G ) or with a 2 carbs manifold ( as 240, 340, 420, XJ6 ) - Michel Gosset

Mike, The 2 carb heads, used on 2..4L, 3.4L and 3.8L sedans and sports cars, except the 150S, use a inlet port spacing that will not allow a 3 carb manifold to be used. I have never seen a Weber manifold made for that spacing. I have seen a one-off triple 2 barrel SU set-up on a 120. Very special and ultra rare. The 150S, E-types and 4.2L engines used the straight port head that will accept 3 carb manifolds, SU or Weber. Also a 2 2" manifold from the 420 sedan. Mike, does that help? - George Badger

George, I agree; This is almost exactly what I tried to explain.. Except that you can find very nice Weber manifolds on " Non Straight Port heads " on C and D Types. To be complete ( but difficult to fit in a 120 ) you can have a Wide angle head with Webers or injection. As for the one-off triple SU , I have been looking for one for many years. Regards - Michel Gosset

All: Is there a study of cylinder head trivia in past digests that would
give a overview of interchangeability, cross-reference, number decoding,
etc for the variations in cylinder heads since they first appeared on the
scene in '48? I am familiar with the difference in the 'C' Vs. Std. but B
heads, straight port heads, etc are a bit of a mystery. At what point did
the intake ports become equidistant?(straight port?) I am considering mixn'
and matchn' bits to put a Jag lump in my Plymour (Jagouth) and have come up
with a late ('57) MKVII package and a 3.8S with O/D package (Package =
engine and transmission complete with starter/gen/carbs, etc). The MKVII
seems the most straight forward, requiring (apparently an XK tailpiece for
the trans and correct inlet manifold. Can the bell housing using hydraulic
clutch be adapted to mech. clutch operation? The 3.8S (from a '64 'S') lump
is less original of course, but interesting in that it had an O/D trans
(shifter position?) and possible performance enhancement opportunities.
Would this head be compatible with the 140 inlet manifold (i.e. port
spacing)? Can tach drive be adapted to mech Vs. electric? Impatience
prevents me at the moment from waiting for the original type pieces to come
available, but that might change. Any and all comments welcome. Thanking
all in advance for advice to get the correct lump and quit #@%&* around
with this oddball %$@!*&. - Bruce Baysinger

Hello Bruce, All the answers to your questions are in Bernard Viart's book
" Le Grand Livre XK" which is in French but easy to understand as they are
presented in charts. He even explained what combinations were feasible
between Blocks and head. I will fax you the pages. Best regards - Michel

Michel: That's great. I look forward to seeing the charts. I would ask you
to try and think of something that I can help you with as the guilt is
becoming almost unbearable. your debt. - Bruce Baysinger

The tacj drive CAN be adapted, and the 3.8"S" head will NIOT accept the
XK-140 manifold, but an XKE manifold WILL fit under the XK-140 bonnet and
wings without any metal bending (need the downward-gooseneck intake
manifolds). Much fun! - Larry Schear, Twin Cam, Inc.

Larry: Thanks for the input. I understand that the O/D gearbox does not
want to live under the stock tunnel as well. so this is pushing me toward
the MKVII unit. Regards - Bruce Baysinger

Larry: After inspecting the 3.8 head (A type) and the 140 manifold, the
port spacing seem OK. Is the difference in the shape of the water passages
the precluding factor? Regards - Bruce Baysinger

Hello Bruce, Here is a chart showing the different types of Cylinder Heads
/ Cylinder Blocks You will see that the same engines can be found on XKs
and Saloons of the same period. However often the induction / water pipes
differ between XKs and saloons. Also what you cannot do is fitting an
induction pipe for SP ( Straight Port) Head on a A, B, or C Head and vice
versa. But you could well fit an XK block with a SP head + induction pipe
...or vice versa an E Type block with a A, B or C Head + pipe Let me know
what "marriage " you envisage; I will give you finer details. ( By the way,
you can see a picture of an early LHD Alloy bodied 120 with a supercharger
in Paul Skiletter's book Jaguar Sports Cars published 11/75 , Pages 66/67 )
Regards - Michel Gosset

YEAR MODEL Cylinder Engine No Prefix=
Cylinder Block No =
Head Type
Early Late

48 - 54 XK 120 3.4 L A ( or C ) W, F C
2331& C2331/1 C4820
( Engine No = ) W
1001 to 2011 W 2012 to W 9999 and F 1001 to

50 - 54 MK 7 3.4 L A ( or C ) A, B, D, N.
( Engine No = ) A,
B, C, & D 1001 to 6722

54 - 57 XK 140 3.4 L A ( or C ) G C
4820 C 8610 C 8610/1
( Engine No = ) G
1001 to G1907 G 1908 to 4430 G 4431 to G 9Ö

54 - 57 MK 7 M 3.4 L A ( or C ) D, N. C
8610 C 8610/1
( Engine No = ) D
6723 to D 9868 D 9869 to N ???

55 - 59 MK 1 2.4 L A BB, BC, BD, BEÖ

56 - 59 MK8 3.4 L B N, NA C
( Engine No = ) N
1001 to NA ????

57 - 59 MK 1 3.4 L B KE, KF. C
8610/1 C 15951
( Engine No = ) KE
1001 to KF 7139 KF 7140 to ????

57 - 61 XK 150 3.4 L A ,then B V C
8610/1 C 15951
( Engine No = ) V
1001 to V 6860 V 6861 to 7600

58 - 61 XK 150 S 3.4 L SP VS C
8610/1 C 15951
( Engine No = ) VS
1001 to VS 2209 VS 1001 to VS 2209

58 - 61 MK 9 3.8 L B NC, NE. C
( Engine No = ) NC
1001 to NE ???

59 - 61 XK 150 3.8 L B VA C
( Engine No = ) VA
1001 to VA 2296

59 - 61 XK 150 S 3.8 L SP VAS C
( Engine No = ) VAS
1001 to VAS 1312

59 - 66 MK 2 3.4 L B KG, KH, KJ. C
17568 C 19293
( Engine No = ) KG
1001 to KH 6480 KH 6481 to ???

59 - 66 MK 2 3.8 L B LA, LB, LC, LD, LEÖ C
17567 C 19983
( Engine No = ) LA
1001 to LC 3826 LC 3827 to LC ????

59 - 67 MK 2 2.4 L B BG, BH, BJ.

61- 72 E Type 3.8 L SP (Straight Port) R, RA

61- 72 E Type 4.2 L SP 7E

61 - 63 E Type LW 3.8 L SP EE

61 - 64 MK 10 3.8 L SP ZA, ZB,Ö C
19292 C 19983 C 22290
1001 to ZB ??? ZA 1001 to ZB ??? ZA 1001 to ZB ???

63 - 68 S Type 3.4 L SP 7B

63 - 68 S Type 3.8 L SP 7B

64 - 66 MK 10 4.2 L SP ZD

66 - 68 420 4.2 L SP 7F

66 - 70 420 G 4.2 L SP ZD

67 - 68 340 3.4 L SP 7J

67 - 68 340 3.8 L SP EE, SE

67 - 69 240 2.4 L SP 7J

68 - 73 XJ 4.2 L SP 7L

68 - 73 XJ 2.8 L SP 7L

Note: You will find the Cylinder Block No embossed on the Carbs side of
engine, just under the Cylinder head gasket

Hi Michel & all -- Michel, once again you've proved the true value of both
this list for xks and the saloons list! The list of cylinder heads/blocks
is INVALUABLE for all of us -- if you don't mind, I'll post it to Alastair
Lauener, who runs the saloons list, to share the wealth -- let me know if
this is OK -- take care -- Larry Martz

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