[xk] XK HEADS Summary

XK
1

To those interested, there is a meal following.
For those not interested, delete immediately.

About time for a wrap-up re the thread on HEADS that I have been pursuing -
there has been a huge amount of contribution both on XK-Lovers over past 10
years, but a lot more direct. There still remain outstanding questions and
some of my conclusions are NOT 100% conclusive by any means, but merely
reflect my opinions drawn from available evidence. I am aware that some of
my conclusions are at odds with long-held folklore, so make up your own
minds.
What follows is a SUMMARY only, but I do have an excel spread sheet where I
detail gathered numbers/sightings etc that on request, I am happy to forward
copies direct. These details will sanitize sources of information, as much
has been obtained on the understanding of privacy.
So although a wrap-up, please if anyone can add to the thread, or debate any
of my conclusions - I am 100% receptive, and note my specific outstanding
QUESTIONS at the end:-

A1. A-type: C2242. (First production XK cylinder head)

  • identified by “XK774 C2242” cast on underside surface middle/inlet side
    field.
  • quick identifier is not having studs for front end of cam covers, so a
    so-called ‘studless head’
  • casting by WILLIAM MILLS (WM) foundry, identified by spark plugs #2/#3 and
    #4/#5 being paired within one Siamesed/oval spark-plug recess.
  • second casting by WEST YORKSHIRE FOUNDRY (WYF) not confirmed.
  • only fitted to XK120s from start at Engine No. W1001 to approximately Dec
    1950.(exact finish engine-numbers as per Spare Parts Catalogue J8)

A1a and A1b. A-type: C2242/1. (Supersedes C2242)

  • this is the same casting as C2242 with only variation to justify the /1
    being the machining of the recess for the seal at the rear of the camshaft,
    with the same rear-seal machining variation made to the mating Cam Covers.
  • thus same “XK774 C2242” cast underside, and thus same “studless”
    cam-covers.
    a - casting by WM as above - with “Siamesed” spark-plug recesses.
    b - casting by WYM now introduced, and identified by all six plugs, having
    individual round recesses.
  • fitted from the first Mark VII saloon engine number A1001 > A7206 and also
    XK120 from December 1950 to W4690. (exact start engine-numbers as per Spare
    Parts Catalogue).

A2a and A2b. A-type: C.6733. (Supersedes C2242/1)

  • quick identifier is now having three-studs added at front of each
    cam-cover.
    a - casting by WM identified by “C6733” over “B235” cast under head at
    rear/inlet field.
    b - casting by WYF identified by “C6733X” over “WM 351” under head at
    middle/exhaust field.
  • fitted to XK120 from W4691 to last F4250 including all to SE specification
    with engine number stamped -8S (and Mark VII from A7207 >) and also to
    “standard” XK140 from G1001 to G6911 (and all Mark VIIM to > N3657, and
    first 2.4 litre saloon BB1001 to BB1152)
    (AND yes - I contend NO XK120SE fitted with -8S engine number heads are
    anything other than C6733 A-type heads - none are C-type)

A3a and maybe A3b. A-type: C6733/1. (Supersedes C6733)

  • no quick identifier from C6733 as the /1 is a result of the casting being
    slightly modified to protect the exhaust-manifold threaded stud holes
    breaking into the water-jacket, so not visible at all with exhaust studs
    fitted.
    a - casting by WYF identified by “C6733-1” over “B235” under head at
    middle/exhaust.
    b - casting by WM not yet identified/seen.
  • fitted to “standard” XK140 G6912 > G9980 (last); Mark VIIM N3658 to N5xxx
    (last) and 2.4 litre (BB1153 to last ).

C1. C-type: C6257. (First C-type head)

  • not yet physically identified, but C6257 is part number shown in C-type
    Spare Parts Catalogue.
  • first used mid 1951 thus suspected to be either a modified C.6733 casting
    or a semi-completed C6257 casting , but detail of any marking unknown, so
    may evolve across both castings.
  • foundry unknown, but guess WYF only.
  • claimed that all can be identified by Head-Sequence-Number Q2xx stamped at
    rear of spark-plug valley.
  • fitted to all XK120.C (C Type) engines E1001 to E1058, and although SB95A
    of April 1953 suggests limited availability as an after-market spare-part
    Assy SD.1025, any so fitted to modify XK120 or Mark VII is likely to be
    minimal and limited to a handful of fully race prepared “works” and favoured
    “privateer” cars.

C2. C-type: C7700. (Supersedes C6257 but not for production supply)

  • listed in J12 Price List of May 1953, but so far only one example
    seen/pictured.
  • identified by “C7700” over “C2” cast on the underside middle/exhaust
    field, thus presumed to be WYF casting.
  • unknown when first used, so possibly on some late build XK120.C to E1058,
    and also possibly as part of Assy SD.1025, but also possibly as core for
    modification to D Type specification/use.

C3a and C3b. C-type: C7707. (Supersedes C6257 for production supply)

  • listed in J12 Price List of May 1953, but actual production supply not in
    place until Oct 1954 for XK140MC )
    a - casting by WYF identified by “C7707” over “C3” cast on the underside
    middle/exhaust field, and a RHxxx sequence-number on front/inlet field. No
    cast ‘C’ in spark-plug valley.
    b - casting presumed WM but unverified. Identified by “C7707” by itself
    cast on the underside middle/inlet field. No cast ‘C’ in spark-plug valley.
  • unknown when first used, so possibly on some late build XK120.C to E1058,
    and also possibly as part of Assy SD.1025, but also as core casting for
    modification/build to D Type specification/use.
  • used on early build XK140MC from G1001 to about G1500, but up to Head
    Sequence-Number AUxxx stamped at rear of spark-plug valley, and very rarely
    to Mark VII.
  • limited availability as a Spare-Part assembly for replacement or for XK120
    for modification/upgrade purposes

C3c and C3d. C-type: C7707. (Supersedes C3a and C3b for production
supply)

  • now quickly identified by addition of a large cast ‘C’ between Spark Plug
    #3 and central core-plug on spark-plug valley.
    c - casting by WYF identified by “C7707” over “C3” with a RHAxxx
    sequence-number adjacent, on the underside middle/exhaust field.
    d - casting by WM unverified but possibly also made.
  • used on later build XK140MC from after about G1500, but after Head
    Sequence-Number AVxxx stamped at rear of spark-plug valley, and very rarely
    to Mark VIIM.
  • limited availability as a Spare-Part assembly for replacement or for XK120
    for modification/upgrade purposes.

C4 C-type: C7707/1. (Supersedes C3c and C3d for production supply)

  • no quick identifier from C7707 as the /1 is a result of the casting being
    slightly modified to protect the exhaust-manifold threaded stud holes
    breaking into the water-jacket, so not visible at all with exhaust studs
    fitted.
  • casting by WYF identified by “C7707-1” over “C3” with a RHCxxx sequence
    number adjacent under head at middle/exhaust.
  • casting by WM not yet identified/seen.
  • fitted to XK140MC G6407 > G9980 (last) and very rarely to Mark VIIM Nxxxx.

D1a and D1b. D-type: C7896. (These are modified/upgraded C-type)

  • identified by C.7707 cast underneath with all numbers ground of and “7896”
    over stamped.
    a - based on C3a casting, thus no cast ‘C’ in spark-plug valley.
  • it would appear that many C7896 heads have Head Sequence Numbers from
    AYxxx sequence, but not all, and most AYxxx Sequence Number heads will NOT
    be C7896.
    b - it is possible that there may be some C7896 heads based on C3b castings
    but at this stage thought unlikely.
  • it is improbable that any C7896 heads will be based on C3c or C3d or C4
    castings, thus will NOT have cast ‘C’ in spark-plug valley.

Other than that - that’s the end of both A-type and C-type Heads.
This thread is not considering later type ‘XK’ Heads, including “Wide-Angle”
D-type Heads, B-type heads as fitted to XK150, Mark VIII and 3.4 litre
saloons, nor “Straight-Port-Heads” as fitted to XK150’S’, nor experimental
heads, 4-cylinder heads nor any other prototype heads.

My main questions are:-

Q1. Details/photos of the C6527 head - C1 above.
Q2. Further evidence of the AUxxx / AVxxx demarcation between - C3a/b and
C3c/d.
Q3. Any more examples of C2.
Q4. Is there a WYF version of A1
Q5. Is there an A3b WM foundry casting.
Q6. Any comments - preferably supported by evidence of anything that
disagrees/contradicts my Summary above.

AS before - there is a LOT of work and effort in putting this together, with
fantastic contribution by many on XK-Lovers - some on-list, but a huge
amount direct off-list.
So I am more than happy to share my data sheet - albeit sanitised re sources
of information.

Print this off guys as its not a 5 minute read, let alone preparing any
responses to my Q1 to Q6.

Roger Payne - XK140MC OTS; E-Type 4.2 S.1 OTS; DSV8.
Canberra.

2

In reply to a message from Roger Payne sent Thu 31 Jan 2013:

Roger,

Thank you for taking the time and trouble to provide us with a
summary of the evidence that backs up your conclusions.

I hope this serves as an example to all of us so that we eventually
migrate away from the usual back and forth about issues of
originality that seem never to get to the point of beng conclusive.
because we do not have a mechanism for arriving at and recording
concensus and we do not have a library in which to collect and
organize evidence on many issues that strike me as unresolved.

Karl–
The original message included these comments:

To those interested, there is a meal following.

–
karl
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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3

In reply to a message from Roger Payne sent Thu 31 Jan 2013:

Excellent meal, garde-manger. Check please.
Is there a chance you have these two lines reversed?
I have an A head with WM351 and always assumed it was a
William Mills product. I will dig it out and post some
photos but we had an ice storm yesterday and the shed door
lock is frozen and my propane torch is inside.–
The original message included these comments:

a - casting by WM identified by ‘‘C6733’’ over ‘‘B235’’ cast under head at
b - casting by WYF identified by ‘‘C6733X’’ over ‘‘WM 351’’ under head at

–
XK120 FHC, Mark V saloon, XJ12L Series II, S-Type 3.0
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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4

To those interested, there is a meal following.

Roger P;
GOOD STUFF!!!
Charles #677556.----- Original Message -----
From: “Roger Payne”
Subject: [xk] XK HEADS Summary.

5

In reply to a message from cb@XKTX.Org sent Thu 31 Jan 2013:

MR. PAYNE, MR.KIRKMAN, MR.BISHOP

Thanks Roger for tabulating variations in the heads.

Here are the numbers from the C head from my 140. This
head seems to be a C3 version, with the C on a square pad
in the valley.

Engine G8931-8S

On the exhaust side, beneath the exhaust ports:
C7707-1 RHE448
C3

On the exhaust side above the exhaust ports:
a circle with T21 in it, then a square with 47 in it
then N2 all upside down

At the rear of the valley:
BM787

The vertical rear surface of the head has a:
W

It has the WY in a circle symbol underneath on the intake
side near the front.–
Gary Grant S818919DN
Ottawa, Canada
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6

Well done Rob,

Glad someone is reading.
Yes - the two are reversed.
The WM in WM351 does indicate WILLIAM MILLS,

So cut & paste:-

A2a and A2b. A-type: C.6733. (Supersedes C2242/1)

  • quick identifier is now having three-studs added at front of each
    cam-cover.
    a - casting by WM identified by “C6733X” over “WM 351” under head at
    middle/exhaust field.
    b - casting by WYF identified by “C6733” over “B235” cast under head at
    rear/inlet field.
  • fitted to XK120 from W4691 to last F4250 including all to SE specification
    with engine number stamped -8S (and Mark VII from A7207 >) and also to
    “standard” XK140 from G1001 to G6911 (and all Mark VIIM to > N3657, and
    first 2.4 litre saloon BB1001 to BB1152) (AND yes - I contend NO XK120SE
    fitted with -8S engine number heads are anything other than C6733 A-type
    heads - none are C-type)

Roger Payne - XK140MC OTS; E-Type 4.2 S.1 OTS; DSV8.
Canberra.-----Original Message-----
From: owner-xk@jag-lovers.org [mailto:owner-xk@jag-lovers.org] On Behalf Of
Rob Reilly
Sent: Friday, 1 February 2013 1:21 AM
To: xk@jag-lovers.org
Subject: Re: [xk] XK HEADS Summary.

In reply to a message from Roger Payne sent Thu 31 Jan 2013:

Excellent meal, garde-manger. Check please.
Is there a chance you have these two lines reversed?
I have an A head with WM351 and always assumed it was a
William Mills product. I will dig it out and post some
photos but we had an ice storm yesterday and the shed door
lock is frozen and my propane torch is inside.

The original message included these comments:

a - casting by WM identified by ‘‘C6733’’ over ‘‘B235’’ cast under head at
b - casting by WYF identified by ‘‘C6733X’’ over ‘‘WM 351’’ under head at

–
XK120 FHC, Mark V saloon, XJ12L Series II, S-Type 3.0
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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7

Thanks Gary,

Totally consistent West Yorkshire Foundry (The W, Y and F initials make up
the symbol you are describing).
The RHE448 is second latest Head Sequence Number so far recorded, but still
a lot to resolve about exact significance of these.

Roger Payne - XK140MC OTS; E-Type 4.2 S.1 OTS; DSV8.
Canberra.-----Original Message-----
From: owner-xk@jag-lovers.org [mailto:owner-xk@jag-lovers.org] On Behalf Of
Gary Grant
Sent: Friday, 1 February 2013 6:15 AM
To: xk@jag-lovers.org
Subject: Re: [xk] XK HEADS Summary.

In reply to a message from cb@XKTX.Org sent Thu 31 Jan 2013:

MR. PAYNE, MR.KIRKMAN, MR.BISHOP

Thanks Roger for tabulating variations in the heads.

Here are the numbers from the C head from my 140. This
head seems to be a C3 version, with the C on a square pad
in the valley.

Engine G8931-8S

On the exhaust side, beneath the exhaust ports:
C7707-1 RHE448
C3

On the exhaust side above the exhaust ports:
a circle with T21 in it, then a square with 47 in it
then N2 all upside down

At the rear of the valley:
BM787

The vertical rear surface of the head has a:
W

It has the WY in a circle symbol underneath on the intake
side near the front.

–
Gary Grant S818919DN
Ottawa, Canada
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8

In reply to a message from Roger Payne sent Thu 31 Jan 2013:

Roger,

It’s been my impression, from viewing close-up photos of D-Types,
that those without the wide angle cylinder heads had the ‘‘C’’
casting in the cylinder head valley.

Today I went through all the D-type photos on
www.coventryracers.com. There are only three cars on that website
with clear photos of the cylinder head valleys. But each of those
cylinder heads has the ‘‘C’’ casting. See XKD 524, XKD 537 and XKSS
701.

I’ve seen photos of several other D-Types with the ‘‘C’’ casting, but
I can’t lay my hands on those photos at this moment.–
The original message included these comments:

D1a and D1b. D-type: C7896. (These are modified/upgraded C-type)

  • identified by C.7707 cast underneath with all numbers ground of and ‘‘7896’’
    over stamped.
    a - based on C3a casting, thus no cast ‘C’ in spark-plug valley.
  • it would appear that many C7896 heads have Head Sequence Numbers from
    AYxxx sequence, but not all, and most AYxxx Sequence Number heads will NOT
    be C7896.
    b - it is possible that there may be some C7896 heads based on C3b castings
    but at this stage thought unlikely.
  • it is improbable that any C7896 heads will be based on C3c or C3d or C4
    castings, thus will NOT have cast ‘C’ in spark-plug valley.

–
Mike Balch
Iowa, United States
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9

I am really pleased to hear this Mike, as I was having trouble reconciling
the advice that “most D-Type” heads had “AYxxx” Head-sequence-numbers, with
also the advice that they did not have cast ‘C’.
It is possible given current understanding of Head Sequence Numbers not
necessarily being in same sequence as Casting-Sequence-Number, as per the
two examples discussed of later heads, not having the cast ‘C’.

Current demarcation for heads without cast ‘C’ is up to AUxxx, and those
with cast ‘C’ from AVxxx on, so normally that would include all the D-type
heads with AYxxx head-sequence-numbers.

This is why photos/solid evidence is needed.

Any photos you can provide, or point me to would be great, but the more
numbers visible improves confidence of head being what it is supposed to be,
and it’s hard to get “under-head” photos at the best of times.
Can you see at least the Head-Sequence-Number and/or the Engine-Number with
these? I will check their web-site.

You have done well - not easy to see detail with these photos - not a
popular angle!

But I do agree - these three examples and the AYxxx sequence number advice
is more probable with the cast ‘C’ so the reality is again, let the AUxxx /
AVxxx demarcation be the best guess until conclusive sightings/photos are
available.

Certainly XKD524 looks amazingly original, but you have to wonder how many
D-types/XKSS still run their original heads, given race-reliability is major
consideration, rather than having the original head-sequence-number given
the relative availability of ex-XK140 C-type heads?

Roger Payne - XK140MC OTS; E-Type 4.2 S.1 OTS; DSV8.
Canberra.-----Original Message-----
From: owner-xk@jag-lovers.org [mailto:owner-xk@jag-lovers.org] On Behalf Of
Mike Balch
Sent: Friday, 1 February 2013 11:44 AM
To: xk@jag-lovers.org
Subject: Re: [xk] XK HEADS Summary.

In reply to a message from Roger Payne sent Thu 31 Jan 2013:

Roger,

It’s been my impression, from viewing close-up photos of D-Types,
that those without the wide angle cylinder heads had the ‘‘C’’
casting in the cylinder head valley.

Today I went through all the D-type photos on
www.coventryracers.com. There are only three cars on that website
with clear photos of the cylinder head valleys. But each of those
cylinder heads has the ‘‘C’’ casting. See XKD 524, XKD 537 and XKSS
701.

I’ve seen photos of several other D-Types with the ‘‘C’’ casting, but
I can’t lay my hands on those photos at this moment.

The original message included these comments:

D1a and D1b. D-type: C7896. (These are modified/upgraded C-type)

  • identified by C.7707 cast underneath with all numbers ground of and
    ‘‘7896’’
    over stamped.
    a - based on C3a casting, thus no cast ‘C’ in spark-plug valley.
  • it would appear that many C7896 heads have Head Sequence Numbers from
    AYxxx sequence, but not all, and most AYxxx Sequence Number heads will NOT
    be C7896.
    b - it is possible that there may be some C7896 heads based on C3b
    castings
    but at this stage thought unlikely.
  • it is improbable that any C7896 heads will be based on C3c or C3d or C4
    castings, thus will NOT have cast ‘C’ in spark-plug valley.

–
Mike Balch
Iowa, United States
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10

In reply to a message from Roger Payne sent Thu 31 Jan 2013:

Roger,

Another sighting of the ‘‘C’’ casting is XKD 517. Several years ago,
Octane Magazine did a comprehensive story on that D-Type, and as I
remember there was a clear photo of the cylinder head valley.
Whether its cylinder head is original from the factory is another
matter. That D-Type has been restored a couple of times.–
Mike Balch
Iowa, United States
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11

Thanks Mike,

The nature of C-types and D-types are not reliable observations unless other
numbers are also verified, but the more sightings the more probability of
being a sound conclusion.

Roger Payne - XK140MC OTS; E-Type 4.2 S.1 OTS; DSV8.
Canberra.-----Original Message-----
From: owner-xk@jag-lovers.org [mailto:owner-xk@jag-lovers.org] On Behalf Of
Mike Balch
Sent: Friday, 1 February 2013 11:57 PM
To: xk@jag-lovers.org
Subject: RE: [xk] XK HEADS Summary.

In reply to a message from Roger Payne sent Thu 31 Jan 2013:

Roger,

Another sighting of the ‘‘C’’ casting is XKD 517. Several years ago,
Octane Magazine did a comprehensive story on that D-Type, and as I
remember there was a clear photo of the cylinder head valley.
Whether its cylinder head is original from the factory is another
matter. That D-Type has been restored a couple of times.

–
Mike Balch
Iowa, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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12

In reply to a message from Roger Payne sent Fri 1 Feb 2013:

Roger

Thank you very much for consolidating years of talk and
discussions; you have given us an excellent synopsis. I also
believe there are myths to dispel.

A couple of differences of opinion on the XK120 C Type
heads. One just a strong belief and the second supported
with evidence.

It seems odd to me that C6257 would be based on a cylinder
head with a greater part number, C6733, as the greater
number would imply a later production date. Cylinder head
C6733 (with 6 additional cam studs) was introduced in April
1952 and the �C� head C6257 had been listed 6 months earlier
in the �C� Type Parts Catalog of November 1951.

Neither C7707 nor C7700 are listed in the J12 Price List of
June 1953. The listing numbers in this publication go up to
C7727; which would indicate the cylinder head part numbers
had been allocated but were not for sale to the public.

Service Bulletin 95A of April 53 announced the C Type head
assembly SD.1025 but the cylinder head part number is not
detailed in the bulletin. As this Bulletin pre-dates the J12
publication by 3 months it implies, to me at least, that the
C Type cylinder head part included in the cylinder assembly
could be be the only listed part in the publication i.e
C6257. The J12 monthly Cumulative Supplements may ‘announce’
C7707 post June 1953 but if not before summer 1954 when
XK120 production ceased then we can conclude that any C Type
head fitted to an XK120 (if indeed any existed) was C6257
and not C7707.

Best regards
Simon
S680732–
sroope
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13

Having personally seen and photograhed just on 75% of all D types built and
with other records I have I was able to supply about 20 D type Head casting
numbers with AY prefix supplied to Roger all these heads have the cast “C”
in the valley therfore you could say the standard production D type ie not
XKC4 series and the 6 series cars and factory cars had a standard C7707 head
with cast “C” in valley then machined/fettled to D specs and 7707 from part
number chiselled of inc for some reason the C3, none of the pics I have look
like they have been ground off and then the 7896 stamped on.
There is no doubt a standard D type head has a cast “C” in valley
terryDate: Fri, 1 Feb 2013 17:42:54 +1100
From: “Roger Payne” rogerpayne@bigblue.net.au
Subject: RE: [xk] XK HEADS Summary.

I am really pleased to hear this Mike, as I was having trouble reconciling
the advice that “most D-Type” heads had “AYxxx” Head-sequence-numbers, with
also the advice that they did not have cast ‘C’.
It is possible given current understanding of Head Sequence Numbers not
necessarily being in same sequence as Casting-Sequence-Number, as per the
two examples discussed of later heads, not having the cast ‘C’.

Current demarcation for heads without cast ‘C’ is up to AUxxx, and those
with cast ‘C’ from AVxxx on, so normally that would include all the D-type
heads with AYxxx head-sequence-numbers.

D1a and D1b. D-type: C7896. (These are modified/upgraded C-type)

  • identified by C.7707 cast underneath with all numbers ground of and
    ‘‘7896’’
    over stamped.
    a - based on C3a casting, thus no cast ‘C’ in spark-plug valley.
  • it would appear that many C7896 heads have Head Sequence Numbers from
    AYxxx sequence, but not all, and most AYxxx Sequence Number heads will NOT
    be C7896.
    b - it is possible that there may be some C7896 heads based on C3b
    castings
14

In reply to a message from Terry McGrath sent Fri 1 Feb 2013:

Perhaps my 2 '‘D’'type heads are bogus but I doubt that since I’ve
own them over thirty years. One was purchased at the Carlisle flea
market either the first or second year of that event with the
45deco3 Webbers and intake manifold intact. It definitely has a C
cast in the center valley. The other one was purchased from Milt
Bernstein who purchased most of Jaguar’s Long Island obsolete parts
when they moved to New Jersey. This head was supposedly a spare
used by MOMO racing. It clearly also has a C in the valley,
however for an engine number only D-TYPE appears. Racing teams
certainly did many strange things but I would believe this team
would have access to the ‘‘better grade’’ parts than most. Whether
or not it was ever used, I don’t know. All surfaces were like new.
I used were, because it now sit on top of my FHC engine. Yes it is
quicker than many 120s–
John Gerhard
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15

Yes Terry,

The three pictures Mike pointed to are the best evidence produced to date
that a genuine D-type head will most likely have cast ‘C’, and this is now
consistent with the theory, following your advice/list of predominantly
AWxxx and AYxxx head-sequence-numbers on D-type heads, given the now
established likely AUxxx/AVxxx demarcation point of non-cast’C’/with-cast
‘C’ heads.

But as noted earlier, I am now focusing more, that the RHxxx, RHAxxx casting
sequence number will reveal the exact demarcation point as this is the
sequence number that is CASTING relevant, whereas the AU/AVxxx head sequence
number appears now to be subject to significant batching distortion of the
relationship of the two sequence numbers.

It’s a shame you don’t have a similar list of this RHxxx, RHAxxx
casting-sequence-number for all the D-type head sightings, albeit we all
know this is not easily seen/noted, let alone photographed short of pulling
the head off every D-type you see - and that would go down well in the
historic race paddock!.

But your second comment does surprise?
Wasn’t it you that sent me the photos of the head off E2034-9 that clearly
show “7896” overstamping the numbers ground off leaving just the C prefix.
The original cast Cxxxx over xx has all the five “x” having been ground off.
The position of the remaining cast “C” and the grind-marks are 100%
consistent with the usual confirmed C7707 over C3 casting numbers. Or are
you now saying this is a fake D-type head - not impossible of course - many
an Engine Number stamping has been faked, so both the pictured E2034-9
stamping and the underneath C7896 stamping could be faked. Bit sad about
price paid on Ebay for this head if it has been faked.

But I agree - everything suggests the majority of “production” D-type heads
will have the cast ‘C’ in the spark plug valley, but still possible, even
likely that early build D-types may in fact have heads based on the earlier
no cast ‘C’ C7707 over C3 head castings, or indeed the C7700 over C2 head
casting.
Need to keep these possibilities alive.

Roger Payne - XK140MC OTS; E-Type 4.2 S.1 OTS; DSV8.
Canberra.-----Original Message-----
From: owner-xk@jag-lovers.org [mailto:owner-xk@jag-lovers.org] On Behalf Of
Terry McGrath
Sent: Saturday, 2 February 2013 10:51 AM
To: xk@jag-lovers.org
Subject: [xk] XK HEADS Summary.

Having personally seen and photograhed just on 75% of all D types built and
with other records I have I was able to supply about 20 D type Head casting
numbers with AY prefix supplied to Roger all these heads have the cast “C”
in the valley therfore you could say the standard production D type ie not
XKC4 series and the 6 series cars and factory cars had a standard C7707 head

with cast “C” in valley then machined/fettled to D specs and 7707 from part
number chiselled of inc for some reason the C3, none of the pics I have look

like they have been ground off and then the 7896 stamped on.
There is no doubt a standard D type head has a cast “C” in valley
terry

Date: Fri, 1 Feb 2013 17:42:54 +1100
From: “Roger Payne” <@Roger_Payne2>
Subject: RE: [xk] XK HEADS Summary.

I am really pleased to hear this Mike, as I was having trouble reconciling
the advice that “most D-Type” heads had “AYxxx” Head-sequence-numbers, with
also the advice that they did not have cast ‘C’.
It is possible given current understanding of Head Sequence Numbers not
necessarily being in same sequence as Casting-Sequence-Number, as per the
two examples discussed of later heads, not having the cast ‘C’.

Current demarcation for heads without cast ‘C’ is up to AUxxx, and those
with cast ‘C’ from AVxxx on, so normally that would include all the D-type
heads with AYxxx head-sequence-numbers.

D1a and D1b. D-type: C7896. (These are modified/upgraded C-type)

  • identified by C.7707 cast underneath with all numbers ground of and
    ‘‘7896’’
    over stamped.
    a - based on C3a casting, thus no cast ‘C’ in spark-plug valley.
  • it would appear that many C7896 heads have Head Sequence Numbers from
    AYxxx sequence, but not all, and most AYxxx Sequence Number heads will NOT
    be C7896.
    b - it is possible that there may be some C7896 heads based on C3b
    castings
16

In reply to a message from Roger Payne sent Fri 1 Feb 2013:

As promised, some pictures of an A head from William Mills
with C6733X and WM351 cast in, and DTD424 stamped
afterwards. Also a curious little 12 spoke sun stamp and a
few others.

http://www.jag-lovers.org/snaps/snap_view.php3?id=1359826032

Google turned up a 1955 article in Flight magazine about the
British light alloy aluminium industry, explaining that
DTD424 is a general purpose aluminium casting alloy invented
and patented in 1939 by Percy Pritchard, director of the
Birmingham Aluminium Casting Co., and was used in WW2
throughout the aircraft industry without payment of royalties.

Woldman’s Engineering Alloys says the composition of DTD424
is Silicon 5 percent, Copper 3 percent, Manganese 0.5
percent, balance Aluminum. For sand castings, tensile
strength is 20,200; 12,300 yield strength; elongation is 2.5
percent; Brinell hardness is 65 and it is supposed to be
corrosion resistant.

Another reference on a Vincent motorcycle site claimed the
composition of DTD424 was Silicon 3-6 percent, Copper 2-4
percent, Iron 0.8 percent, Manganese 0.7 percent, remainder
Aluminum.

I wonder if substandard metallurgy, traces of iron in there
would contribute to an increase in corrosion? Has anyone
noticed, is corrosion more frequently seen in a West
Yorkshire head vs a William Mills head?–
XK120 FHC, Mark V saloon, XJ12L Series II, S-Type 3.0
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17

In reply to a message from Rob Reilly sent Sat 2 Feb 2013:

Isn’t 65 Brinell a bit soft for heads.

I was talking to Cranky’s last week ’ as we were making new alloy
SS1 heads and the foundry had quoted for 85 Brinell after heat
treatment.
They said that was OK, 100 was ideal and 60 was too soft.

I wonder if , or how many, places welding up corrosion in alloy
heads use a similar rod to that to put teh ’ corrosion resistence ’
back .–
The original message included these comments:

DTD424 is a general purpose aluminium casting alloy invented
and patented in 1939 by Percy Pritchard, director of the
Birmingham Aluminium Casting Co., and was used in WW2
throughout the aircraft industry without payment of royalties.
Woldman’s Engineering Alloys says the composition of DTD424
is Silicon 5 percent, Copper 3 percent, Manganese 0.5
percent, balance Aluminum. For sand castings, tensile
strength is 20,200; 12,300 yield strength; elongation is 2.5
percent; Brinell hardness is 65 and it is supposed to be
corrosion resistant.

–
Ed Nantes SS
Melbourne, Australia
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18

G’day Simon,

Hopefully the promised photos of a genuine original head from an actual
C-type will provide at least our FIRST solid evidence, so we can modify our
speculation one way or the other.

  1. The reason I have said the C6257 head may be based on the C6733 A-type
    head, is all to do with the three studs at front of camshafts.

A C2242 and a C2242-1 head does not have these three studs, and as all
C-types engines I have seen in photos/actual cars have cam-covers with these
three front studs.

So only head casting available is an unlisted prototype head - possible, or
more likely a modified C6733 head that may well have been in development a
little earlier than its first in-production use.

But certainly a guess, and hopefully promised photos will either confirm or
kill this guess.

  1. I don’t know - but my thought is numbers were allocated sequentially as
    needed, so C7700 and C7707 would appear to have been allocated in June 1953,
    so regardless of when C7700 and C7707 heads were actually available for sale
    to the public, they may well have existed and been used for latter C-type
    production before being offered/listed in J12.
    I would imagine Jaguar would have wanted to minimise the number of C6257
    heads used, that seem to have been hand-finished, and would have wanted to
    use as cast-heads requiring minimal hand working, and preferably no hand
    working. Privately I speculate that the C7700 head may have been a
    suitably revised head-casting but an intermediate semi-finished head
    casting, and the C7707 head a finished head casting. Why else the price
    difference?. Problem is this C6257 > C7700 > C7707 progression is so far
    of unknown time-frame. There HAS to be a reason that the C7700 head is
    also marked C2, whilst the C7707 is C3 Certainly the C7707 head was ready
    for the first production XK140 in Oct 1954, but we have a major lack of
    sightings/evidence from June 1953 to September 1954 which I suspect is
    because priority was given to supplying these various stages and various
    amounts of hand-finishing of C-type heads to works race cars, then
    production customer C-types, with a dribble going to XK120 “favoured” race
    teams, and so far, none to production XK120s.

But again - strong and reliable evidence is paramount - photos.

I also have interests re the C7707 head pictured in Urs Schmid’s Volume 1.

It does not appear to be a WYM C7707 over C3, so what is it?
So far Urs cannot shed any additional light - he got back to me this morning

  • but he is searching!

Regards,

Roger

Roger Payne
8 Beggs Place
MACARTHUR
A.C.T. 2904
Australia-----Original Message-----
From: owner-xk@jag-lovers.org [mailto:owner-xk@jag-lovers.org] On Behalf Of
sroope
Sent: Saturday, 2 February 2013 9:15 AM
To: xk@jag-lovers.org
Subject: RE: [xk] XK HEADS Summary.

In reply to a message from Roger Payne sent Fri 1 Feb 2013:

Roger

Thank you very much for consolidating years of talk and
discussions; you have given us an excellent synopsis. I also
believe there are myths to dispel.

A couple of differences of opinion on the XK120 C Type
heads. One just a strong belief and the second supported
with evidence.

It seems odd to me that C6257 would be based on a cylinder
head with a greater part number, C6733, as the greater
number would imply a later production date. Cylinder head
C6733 (with 6 additional cam studs) was introduced in April
1952 and the ‘C’ head C6257 had been listed 6 months earlier
in the ‘C’ Type Parts Catalog of November 1951.

Neither C7707 nor C7700 are listed in the J12 Price List of
June 1953. The listing numbers in this publication go up to
C7727; which would indicate the cylinder head part numbers
had been allocated but were not for sale to the public.

Service Bulletin 95A of April 53 announced the C Type head
assembly SD.1025 but the cylinder head part number is not
detailed in the bulletin. As this Bulletin pre-dates the J12
publication by 3 months it implies, to me at least, that the
C Type cylinder head part included in the cylinder assembly
could be be the only listed part in the publication i.e
C6257. The J12 monthly Cumulative Supplements may ‘announce’
C7707 post June 1953 but if not before summer 1954 when
XK120 production ceased then we can conclude that any C Type
head fitted to an XK120 (if indeed any existed) was C6257
and not C7707.

Best regards
Simon
S680732

–
sroope
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19

That’s great Rob,

100% consistent with other William Mills 3rd-version A-type heads.
This is exactly the same A-type head now verified on several XK120SE
engines, with Wxxxx-8S and Fxxxx-8S engine numbers, and also on standard
XK140s.

So far, no sign of a CASTING-SEQUENCE number on WM heads (as per the WYF
C-type heads) so the Head Sequence Number BA271 stamped at rear of spark
plug valley is best indicator of age given the lack of any stamped ENGINE
NUMBER.

I have a number of confirmed sightings of other AX/BA Head Sequence Numbers
on 1955 XK140 Gxxxx-8 engines, so as Rob speculates, this unnumbered head
was probably a spare-part head from that period. Interestingly one of these
C6733X A-type heads has AY829 Head-Sequence-Number which does of course
suggest being in the head machining/assembly shop at same time as all the
AYxxx heads that Terry advised against 14 or so D-type heads, but surely
more evidence that this is a Jaguar machining/assembly number and nothing to
do with the foundry - with WM and WYM heads, and A-type, C-type and D-type
heads all intermixed.

The stamps showing a JAGxx in an oval are believed to be quality-control/
inspection stamps by Inspector No. xx following periodic qc inspections, so
someone will have been inspector No.96

The DTD424 revelation is most interesting - good bit of detective work Rob.
Funny thing to stamp on a head unless of course Jaguar were experimenting
with alloy variations.

Other credible references say the first C2242 heads were cast from RR.50
aluminium alloy. Will have to dig out the old Engineering Materials
text/reference books and see how they compare - oops, showing my age - I
will google it, although does that make 1950s information more up to date?

I think corrosion is more to do with the water used and use or not of
anti-corrosion additives, but the alloy may affect susceptibility to
corrosion.
For years locally, you could tell whether a bare cylinder head was ex
Melbourne car or ex Sydney car by the amount of corrosion with
coolants/ant-corrosion additives not commonplace in Australia in 1950s/60s
as seems to have been the case in USA - so just “good water” or “bad water”
(respectively) for topping up radiator.

Roger Payne - XK140MC OTS; E-Type 4.2 S.1 OTS; DSV8.
Canberra.-----Original Message-----
From: owner-xk@jag-lovers.org [mailto:owner-xk@jag-lovers.org] On Behalf Of
Rob Reilly
Sent: Sunday, 3 February 2013 9:08 AM
To: xk@jag-lovers.org
Subject: RE: [xk] XK HEADS Summary.

In reply to a message from Roger Payne sent Fri 1 Feb 2013:

As promised, some pictures of an A head from William Mills
with C6733X and WM351 cast in, and DTD424 stamped
afterwards. Also a curious little 12 spoke sun stamp and a
few others.

http://www.jag-lovers.org/snaps/snap_view.php3?id=1359826032

Google turned up a 1955 article in Flight magazine about the
British light alloy aluminium industry, explaining that
DTD424 is a general purpose aluminium casting alloy invented
and patented in 1939 by Percy Pritchard, director of the
Birmingham Aluminium Casting Co., and was used in WW2
throughout the aircraft industry without payment of royalties.

Woldman’s Engineering Alloys says the composition of DTD424
is Silicon 5 percent, Copper 3 percent, Manganese 0.5
percent, balance Aluminum. For sand castings, tensile
strength is 20,200; 12,300 yield strength; elongation is 2.5
percent; Brinell hardness is 65 and it is supposed to be
corrosion resistant.

Another reference on a Vincent motorcycle site claimed the
composition of DTD424 was Silicon 3-6 percent, Copper 2-4
percent, Iron 0.8 percent, Manganese 0.7 percent, remainder
Aluminum.

I wonder if substandard metallurgy, traces of iron in there
would contribute to an increase in corrosion? Has anyone
noticed, is corrosion more frequently seen in a West
Yorkshire head vs a William Mills head?

XK120 FHC, Mark V saloon, XJ12L Series II, S-Type 3.0
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20

In reply to a message from Roger Payne sent Sun 3 Feb 2013:

I wondered about that as well, why stamp the material spec
on all the heads, unless it had to do with machinability and
was for the machinist’s benefit.

Google the 1950s information (scanned but originally printed
in books) Flight article and Woldman’s again turns up that
the RR series of alloys trade named Hiduminium was patented
by Rolls Royce for aircraft use and licensed to High Duty
Alloys. Later on Birmingham Aluminium Casting Co. was
producing it, and the chemistry is Cu 0.8-2 percent, Fe
0.8-1.4 percent, Mg 0.05-2, Ni 0.8-1.7, Si 1.5-2.8, Ti 0.2,
balance Al.
Heat treated 25-30ksi Tensile, 3 percent ELongation, 5
percent Reduction in Area, 72 HB (I’m interpreting this as
Brinell Hardness), for cylinder blocks, cylinder heads,
pistons, crankcases, heat treatable.

So if the material was changed from RR50 to DTD424, was this
a technical improvement, or was it for a cost reduction?–
The original message included these comments:

Funny thing to stamp on a head unless of course Jaguar were experimenting
with alloy variations.
Other credible references say the first C2242 heads were cast from RR.50
aluminium alloy. Will have to dig out the old Engineering Materials
text/reference books and see how they compare - oops, showing my age - I
will google it, although does that make 1950s information more up to date?

–
XK120 FHC, Mark V saloon, XJ12L Series II, S-Type 3.0
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