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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