Terry (and others interested)
Presumably you are now talking about the “Casting SEQUENCE Number”, and not
the “Casting PART Number” and certainly not the (cast) Jaguar Part Number?
The “Casting Sequence Number” (not any official name, but what I call it) is
the number that on very early heads was STAMPED just forward of spark-plug
number 4, but later on C7707 (C-type) heads for instance was on the boss
right at the rear of the spark plug valley. Is this what you are saying
your Qxxx numbers are, and if so stamped forward of Plug No.4 or on a boss
at rear of valley?
The “Casting Part Number” is a bit unclear, as depending on the head, you
get all sorts of other numbers cast in, but on the underside. For instance,
a very early XK120 head that has A105 Casting Sequence Number, has under the
head also a cast number XK774 which is presumed to denote an experimental
number or something.
The cast “Jaguar Part Number” is of course what this theme was all about -
and in the above A105/ XK774 example, also under the head is the cast number
C2242 which is of course the Jaguar Part Number of the very first
type/version of the XK “A-type” head, discounting any
pre-production/experimental 6 and 4 cylinder heads.
But the question about the head as used on the C-type racing car, was is it
the part number shown in the C-Type Spare Parts Catalogue - C.6257, which is
also listed in the May 1953 MASTER PRICE LIST, or is it the later C.7707
part number of C-type heads fitted as original equipment to XK140MC from the
first XK140 so equipped, but also offered as a spare-parts supply from
April/May/or later 1953 for upgrading XK120s and Mark VIIs supplied new with
This is the key to this area of doubt.
So of the 3/4 of all the C-types built including other motors sold to HWM
etc, how many had C.6257 part number and how many had C.7707 part number or
was there no Jaguar Part No at all?
AS advised - I have never seen the underside of a head that I confidently
believe is an original C-type racing-car head so don’t know, although the
theory suggests that most C-types would have a C.6257 head and probably all
of them, or maybe the last C-types got the newer C7707 casting. Your Q243
to Q290 range of numbers suggests all one batch of maybe/probably C.6257
heads (given the SPC and Price List date), so maybe the next “batch” of
C-type head castings were “revised for some reason/detail” C7707 heads.
Certainly it seems likely that the first batch of C7707 heads did not
include the cast “C” in the middle of the valley, with all known examples to
date having casting sequence numbers prior to AUxxx (earliest seen being
AQxxx), but all examples to date confirmed to HAVE this cast “C” have
casting sequence numbers AVxxx and later (up to at least BHxxx) - with the
one known exception - that being the subject of casting error mistakes
thread. (This is totally separate issue to whether C-type heads fitted
originally to XK140MC were painted RED and had cast TYPE C badges as per
Jaguar period literature, I contend 100% so painted/fitted)
Service Bulletin 95A of April 1953 advises limited availability to special
order a Cylinder Head Assembly as fitted to existing XK.120.C as Assembly
SD.1025 (without giving the Part Number of just the Head)
The June 1953 MASTER PRICE LIST allocates Part Numbers just up to and past
C.7707 but does not include (yet) actual C.7707, but this suggests part
number had been allocated but head so numbered was not yet available for
sale in June 1953, with C.6257 still listed/for sale.
If you too have not seen the underside of any of these 3/4 of all C types
built, then the position of the Qxxx casting sequence number may be a clue.
All the C.7707 heads I have looked at had their casting sequence number on a
boss at the very rear of the valley.
I don’t know where this is on a C.6257 head, but if the Qxxx Casting
Sequence Numbers are either stamped forward of spark plug No.4, or stamped
on the flat (not a boss) at the very rear of the head, then that suggests
that any head so stamped is not a C.7707 head.
This casting sequence number seems to be a very useful guide to any
evolution within castings, being production sequential - whereas Engine
Number stampings can be somewhat random picking of head castings from stock,
to then be machined/built up into a cylinder-head assembly and then its
allocation to which model Jaguar and thus Engine Number series, and thus
then sequential Engine Number stamping.
Roger Payne - XK140MC OTS; E-Type 4.2 S.1 OTS; DSV8.
From: firstname.lastname@example.org [mailto:email@example.com] On Behalf Of
Sent: Saturday, 12 January 2013 1:48 PM
Subject: [xk] XK heads C types
Having viewed over 3/4 of all the C types built including having seen a
couple of the motors sold to HWM etc my observations are
Head casting numbers as fitted to genuine C type Jaguars these do not have a
“C” cast into the vally
Q275 this is in XKC037
Q266 block no P180
Q270 although this has been hand stamped onto a C type head that has clearly
had the old engine number removed
there are a couple of N, W, T and R prefixed numbers inthe early cars and
the later cars had the D type heads usually prefixed AY
With 18 Q casting heads and probably I could find a couple of more checking
records further I reckon 33% having the Q prefix is quite a reasonable
sample and one could draw the conclusion that the average customer delivered
cars not the real early and not the factory cars and late cars the majority
had Q prefixed heads
Date: Fri, 11 Jan 2013 17:33:22 +1100
From: “Roger Payne” <@Roger_Payne2>
Subject: RE: [xk] XK heads
Terry - I am glad you said your GUESS, as the facts/evidence to date do not
support a few of your GUESSES.
I too have not physically verified what casting number may be cast (or
stamped) into the head fitted originally to “Production” C Type racing cars,
but the available literature theory strongly suggests they were designated
and probably/maybe marked C.6257. And as we all know, these bought in
castings from either of the two foundries used, will also have a whole raft
of other identifiers and foundry casting numbers which I don’t think anyone
is remotely close to deciphering, whether it is a Q or X or something else.
The problem with C-types now of course is we only started with a very small
number of them, and the number today that still have their original heads is
even less, let alone accessing them to verify stamped in Engine Number and
associated Jaguar Part Number cast/stamped underneath - and even then this
is not a casual 5 minute exercise, as the chances of a non-original head
being renumbered to seem original is quite high, thus would need a very
informed examination. I have found it almost impossible - well difficult
- to verify any original H8 carburetters still fitted to their original
So we agree there is certainly more work to be done/discovered on original
C-type racing-car heads.
Roger Payne - XK140MC OTS; E-Type 4.2 S.1 OTS; DSV8.