Other than the various numbers, how can one tell if a head is a genuine C-type? I have a 1957 Allard Palm Beach MK II built from new with a Jaguar engine. The cam covers say C-type and are definitely the originals to the car. The stamped number is G9646. Allard records say the engine is a C-type, but how can I know for sure if this is what I have? Some years ago I was told that the very late C-type heads were different from the earlier heads. Is this correct? The Jaguar Heritage Trust have no record of this engine. Their records cover only engines installed in jaguar cars.
Roger Payne is our leading expert on this subject: here is but one of his very informative posts on the subject.
Edward,
There is only one way to be 100% sure, and unfortunately that requires a photograph/details of the cast in letters/numbers on the underside of the head (but the visible part overlapping the block), which identify which of the two foundries that supplied Jaguar, actually made the cylinder head casting, and indeed to what specification it was cast. It also allows an indication of approximate age the head was cast. Once the head casting was made, it was supplied to Jaguar and was introduced in due-course to their machine shop, where all the machining and assembly was done, to then be eventually incorporated in a complete Engine Build, to assemble into a Jaguar or indeed as a spare to supply to others, such as indeed Allard. There are other identifies added by Jaguar…
From the top view, things are not conclusive, but can give a good indication/likelihood as to what type of Head it is and again also its approximate age - the easier ones being the exact ENGINE NUMBER stamped into the vertical face at the forward end of the spark plug valley, and also the HEAD SEQUENCE NUMBER (HSN) stamped into the rear-most flat area at the very back of the spark plug valley - but again photos are best, as these will also reveal any fake/altered identification…
So over to you… your cylinder head can be positively identified…
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Welcome Edward. This forum strives to provide accurate information. We may not know much about Allards, though some of us admire them, but we know about Jaguar engines.
I suspect that there is some misinterpretation as to what is a genuine C-Type engine. If you mean an engine that was installed or intended to be installed in a C-Type racing car, those engines all had serial numbers with the prefix letter E, not G.
A prefix G on the serial number indicates it was made for an XK140, or anyway during the production period of the XK140, if as you say it was sold new to Allard as a crate engine.
Many XK140s had the optional C-Type heads, and those cars were often called X140MC meaning Modified for Competition. There should be a suffix number 8 or 9 indicating the compression ratio, i.e. which optional pistons were installed in the block, and sometimes a suffix letter S like this.
They also usually have a letter C in the valley.
and the casting number C7707 on the underside.
Thus within the broad unofficial definition, an engine originally built with a C head could be called a C-Type engine, meaning Competition, though not actually for a C-Type racing car.
G engines began with G1001 so G9646 would be the 8946th XK140 engine built. XK140 total production from Sept '54 to Jan '57 was 8937 cars (ref Original XK by Porter). There was a fire in the factory in Jan '57 and XK140 production was effectively stopped after that month.
Allowing for spares and replacements, it seems a good guess that your engine was made about Nov/Dec '56 or Jan '57 and sold to Allard, either by a previous arrangement, or because it was redundant at Jaguar after the fire.
So as Roger says, casting and stamped numbers will identify it. You can read those on the underside with a mirror and a flashlight.
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Thanks a million for the help — several replied. Really helpful.
My head is off the block, so it was easy to examine. Fortunately, it is the real thing — C7707 casting number. I have refurbished it, but it did not need much work as it is very low mileage.
By the way, this Allard has an alloy case Moss gearbox and Laycock de Normanville overdrive. Rear axle is XK140.
I owned an XK140MC many years ago, in the USA, when I was college age — did not realize what I had at the time.
Dean
Good morning all, my engine is at the builders here are the numbers . can you wise men tell me the story of how this head got put on my engine block. also there is other parts on with the engine that I think are not original , lots to look over here let me know what you all think.
Chassis # 671124
Engine # W 2498-8 with a C Type Head
Body # F 2913
Gear Box # JH 4889
Not at all unusual for someone to have swapped over a C head from an early A head in the old days. Some do it still. You also have 2" carbs, often referred to as sand cast, meaning a rough outer surface. And your fan and hub have been changed from 5 blade to 6 blade, possibly the entire water pump was changed but that also was not unusual.
You have the correct front mounts.
More unusual are wooden wagon wheels on the rear axle. Very few do that to a 120. 
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Thanks Rob, look deeper there is more what else can you see. I found the original Fan Blades today in a box . Should I use the original fan , I have to order a new water pump anyway . The wagon you see is a Civil War Cannon. I thought all 120 s come with a Cannon.
Dean,
As advised, the numbers tell you everything, and photos of the numbers also tell you whether they are original or faked/altered, bearing in mind some numbers were altered by the factory - but thats a different story…
The pictured cast C7707-1 tells you this is a late 1956 made C-type head casting, with the -1 indicating a slight upgrade to the casting to reinforce the inlet manifold stud hole depth - so nothing affecting the performance, but an initiative to better protect against studs screwed in to far/tight breaking through into the water-jacket. With XK140 heads, this change from C7707 heads to C7707-1 heads happened from engine number G6407-8S onwards.
The cast C3 tells you that this C7707 head is in fact the third generation of C-type heads, as was supplied to all XK140s fitted with a C-type head, noting from late 1954 onwards, after the introduction of these C3 heads, these were what was also supplied as a new spare part to C-type and XK120 customers as well as any heads/engines supplied direct to non-Jaguar customers.
The cast RHF916 is what I call the CSN (Casting Sequence Number) being an internal identifier used by the West Yorkshire Foundries Ltd, that tells you their sequence of making C7707/ C3 head castings, and by comparing with physical data sightings gives an approximate age of the casting, which is in fact getting very close to being one of the last batch made in late 1956 with I estimate the very last one made being probably RHF999, albeit the last one actually confirmed/seen (to date) is RHF998…
I still need to see photos of the ENGINE NUMBER and HSN (Head Sequence Number) on the top side of the Head, but previously you advised an ENGINE NUMBER of G9646 being stamped… this is an important detail as if a factory original stamping there should also be a stamped in suffix, rarely -7S, most usually -8S or also rarely -9S. With the G9646 otherwise indicating originally fitted to a very late 1956 XK140 and not originally supplied new as a spare part, or indeed to another manufacturer (such as Allard) withy these heads not having any Jaguar factory stamped Engine Number.
I only say this as the last batch of C7707-1 / C3 heads were in fact (mostly) supplied new unstamped/no Engine Number as a Spare Part head, and your CSN RHF916 is approaching this final batch, so it would be nice to see/verify the ENGINE NUMBER stamping G9646 being factory original or not… The CSN stamping would provide additional proof/confidence as to exactly what you have.
But so far, my best guess is that your Head is indeed a genuine C-type Head, as cast/made in late 1956, and most probably fitted new to a late 1956 build XK140MC, thus a second hand acquisition if now fitted to your Allard - but bear in mind all this same comment can also identify the BLOCK and GEARBOX that are fitted presumably to your Allard - which may or may not be original to this C-type Head.
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Thanks Roger, here are photos of the gear box and engine block all numbers match the Heritage Certificate. witch confirms the block and gearbox are not original to the C-type head.
The 5 blade fan would need the 5 bolt hub. You might look for that if you prefer to be original spec where you can. Or you can stick with the 6 blade which ought to be a little better for cooling if you are in a hot climate. You can rebuild your water pump if the impeller is in good shape. Water pumps went through a development period from '49-'52 which has been discussed many times on this forum, and for which it would be better to start a new thread.
My 120 came with a grease gun which was called a pom-pom, does that count?
Rob take a close look at the cam covers and the pipe coming off the water pump.
Well, the cam covers having front studs but lacking C-Type badges suggest that they are not original to the car, but came from a different head, different donor car. There will be casting numbers on the inside by which you can identify them.
The pipe coming straight out from the side port on the water pump may be from some sort of amateur heater installation. Usually with a heater installation there were two brass banjos there.
Roger:
Wow — greatly appreciated information. Thank you.
Here is a photo of the engine number — sorry about the focus, but you can read the number.
I can make a better photo later if wanted for your files.
With regard to origin of this engine, one of the engineers who worked on this car is still with us. He says the engine came from Jaguar as a new engine — was not removed from a Jaguar car.
Dean
The 5 blade, propeller style fan predates 1952, while the G series engine is 1956 or so. Which of the two manifolds below does yours most resemble? Top is C7462, XK140, and the bottom is C2377, XK120.
Amazing, all the multitude of changes to this venerable powerplant!
Alone, that would make a good book.
I am not sure Mike the manifold is a the mechanic shop , I will ask him tomorrow to send me a photo of it .
Nothing to add to the thread except to say photos of the car please. 
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Dean, is there a factory commission plate in the engine compartment of the Allard that shows the engine or gearbox number?