As noted, I have been researching Cylinder Heads for many years, and in particular the progression/development of the so called C-TYPE Head, and although I am now confident I can be conclusive as to their development/evolution over their June 1951 to January 1957 period of development/evolution and usage, their are indeed a couple of anomalies and loose-ends to be finalised.
I do have a comprehensive paper half written, fully describing, picturing and explaining the whole C-type head story.
A couple of relevant conclusions.
The C-TYPE head as was offered as a factory optional extra on XK140MC and a handful only Mark VII saloons was the THIRD major variant. It was Jaguar Part Number C7707, and indeed the foundry that made these castings for Jaguar, included the cast in C7707 over a C3 on the underside of the cylinder head. The C7707 casting is obvious, and the C3 is presumed to indicate the third variant of the C-type head. This C7707 over C3 is clearly shown in Rob’s photo, so no point posting another picture. The adjacent RHB527 is an internal foundry reference number, that I call the CASTING SEQUENCE NUMBER (or CSN), and incremented on at a time for each head casting made, but after many years of gathering data, is a most important number that allows the age of the casting to be approximated. This CSN started at RH10 (presumably, with RH70 being lowest number confirmed) and ran up to RHF998 (so far, being the highest number confirmed).
Now these C7707 / C3 castings did NOT initially have the very visible large cast ‘C’ in the middle of the spark plug valley (as shown in Robs third photo), with XK140s so fitted up to engine numbers from G1015-8S up to a high of G1362-8S so confirmed without the cast ‘C’.
From a low of engine number G2183-8S onwards up to a high G9763-8S, C-type heads now did (mostly) include this cast ‘C’. I am aware of the large gap between G1362 and G2183 not yet sighted/confirmed, but note that these engines are not all C-type heads, with many being A-type heads as fitted to ‘standard’ XK140s. (Certainly I would love input from anyone with a C-type head with an ENGINE NUMBER in between G1362-8S and G2183-8S)
But it must be appreciated, that these heads were sand-cast, and typically all cast in numbers/ identifiers were produced by special additional moulds, and as already noted the CSN was changed for each head casting, so they were all individually prepared moulds/castings. There has been a small batch of C-Type heads where the cast in ‘C’ is missing, and clearly never provided for in the sand-casting mould, but with an Engine Number much later than expected, thus reasonably presumed to be a mistake/error. I have been able to closely examine at least four of these, all within a close batch of CSN heads, that after machining, allocation to an Engine, and being allocated to an XK140MC all have engine numbers in the G53xx-8S to G58xx-8S range. You must appreciate however, that it is quite possible that other heads from the same CSN batch without the cast ‘C’, may end up having an Engine Number higher or lower than this range. Indeed apart from this batch with the ‘C’ mould missing, I have been advised that with a sand-casting you could also have potential one offs with a damaged or indeed filled ‘C’ mould.
Regardless - there are enough clues, and enough evidence of Casting Part Numbers, Casting Sequence Numbers (CSN), Head Sequence Numbers (HSN - the RC444 stamping in Robs 4th photo), and actual stamped in Engine Number to identify if a head is a genuine C-type head or not, and indeed its approximate age that can identify if a head is original to a particular XK140MC or not, and indeed of course, reveal the origin of the many XK120s that now have C-type heads fitted aftermarket.
The only other detail constantly debated is the RED paint.
Research to date is now so comprehensive, that it can be considered CONCLUSIVE, so let the nay-sayers prove otherwise. The XK140 Owners Handbook which was prepared prior to the XK140 launch in October 1954 clearly announces the availability of the C-type head and being identified by being painted RED. Note - no mention of the cast in ‘C’ as that wasn’t added until early 1955.
The C7707 / C3 C-type head can be considered the ‘production’ version of the C-type head, first available from the first XK140MC - so far from as early as G1015-8S and onwards, and always originally painted RED. RED paint is not permanent as is casting numbers and cast in ‘C’, so there is no surprises at all when people 60 yeras later find a C-type head with minimal or indeed no red-paint remaining. Indeed many a head has been cleaned in a chemical bath, which 100% removes any existing red paint.
The only debate is where the RED paint is applied, and again there are many opinions given the fact that 60 yeras later, there may be little signs of remaining red paint in all original areas, and indeed there is no actual reason why a head painted RED in October 1954 was still painted RED exactly the same way in January 1957.
MY conclusions based on many yeras of specifically seeking out original red painted heads is:-
- The entire spark-plug valley was painted RED, from the curved-edge at the front just above the engine number stamping, all the way down to the rear of the valley and indeed over to the rear of the head. The sides of the valley were painted right up to the cam-cover gasket joint, so most definitely over the machined sides - which amazingly some people mask and don’t paint.
- The complete rear of the head, but noting the gasket surfaces for oil pipes were not.
- There was NO red paint at all on the INLET side of the head.
- There was definitely NO red paint on the FRONT of the head.
- The only area of debate is the EXHAUST side, and indeed I now tend to think it did vary based on Oct 1954 to January 1957 age, and indeed maybe overlapping batches.
There is some evidence that some heads were not painted RED at all on the exhaust side.
The overwhelming majority were however painted red along the rough-cast area above the exhaust manifolds, and blending around the curve of the timing chain housing.
And a large number also had red paint on the machined strip between the front and rear manifolds, whether deliberately here, or overspray from the deliberate top strip is debateable.
Not mentioned above, but from mid/late 1956, there was a slight modification made to the C7707 / C3 C-type head casting, that warranted a new Jaguar Part Number C7707/1 that is visible now on the castings as C7707-1 / C3
And note - no comments hear about the earlier variants/developments of the C-type head as fitted standard equipment on C-type racing cars, and made available to other special order for other competition applications as per the ‘infamous’ Service Bulletin 95B.