Cylinder Head Question

I have a cylinder head with the following stamps:
C7707-1 with C5 underneath
I know that C7707 is the Jaguar part number for a C Type head, can anyone decode the C5 stamp and the RHF952 sequence number as to date and who the foundry was?

Welcome Stephen.
C5 may be a mold pattern number. RHF952 is a production sequence numbers, but we really need more sightings in order to make a guess as to their meaning.
The engine serial number at the front and the production sequence stamped number at the rear are more helpful if you can provide those.
Here is the West Yorkshire logo.
The other foundry is William Mills which is usually designated with a WM.

Hi Rob,
Thanks for the response. Here are a couple of images of the head.

The last image shows the symbol for WYF so thanks for helping confirm that point.
My understanding is that the C* stamp under the C7707 refers to the head modifications that would have been current at the time of casting ie design.
I have no idea of the significance of the RHF952.
The engine number is not stamped on the head and there is no sequence number as you suggest, it must have been a replacement at some point.
Perhaps at this time the HSN was embedded within the RHF number?


The numbers tell you all…
The C7707-1 cast number on the underside of the head tells you its Jaguar Part Number, C7707/1 which is a C-type head, but the final variant introduced in mid 1956, where the inlet manifold stud holes were modified, relative to the original C7707 part number head.
You will also find it is NOT a cast C5 underneath the C7707-1 cast number, but instead a C3 - and this simply denotes being the third main variant of of C-type head casting which applied to both C7707 and C7707-1 heads.
The overlapping WYF cast letters, is the logo for the West Yorkshire Foundry, one of the two foundries from whom Jaguar sourced all their Cylinder Head Castings.

You will also see the RHF952 cast number - this is the CASTING SEQUENCE NUMBER (CSN) as allocated by the WYFoundry. THese do give you a good indication of when the casting was actually made, but although indicative, does not directly tell you the age of that Jaguar machine shop actually machined up and assembled the completed Head. You haven’t advised, but there is another stamped in number at the rear of the spark plug valley that Jaguar machine shop stamped in during their head manufacturing process - this is what I call the HEAD SEQUENCE NUMBER (HSN) and is a more accurate dating indicator… Can you advise, and provide a photo of your HSN stamping. I am guessing by other clues, it will be most likely BZxxx.

So what you have is a final variant C-type head, Jaguar Part Number C7707/1 with the casting made by West Yorkshire Foundry. You have advised that their is no ENGINE NUMBER stamped at the front of the head, which indicates head was never actually allocated/fitted to an actual XK140 or Mark VIIM by the factory (factory fitted C-type heads to Mark VII and Mark VIIM are extremely rare, but they do exist). So this head was most probably a spare new head, supplied as spare parts stock to a Jaguar Dealership.

The CSN of RHF952 is getting extremely close to the last C-type head casting made, and indeed seems to be a small batch of heads at the end made up into complete C-type heads as spare parts stock, after the last heads were factory used/allocated to XK140MC. I would like to know your HSN to be surer, but for want of a reasonably educated guess, I would suggest this head was actually made/completed by Jaguar after the last XK140 was made, so say cJanuary 1957 and immediately allocated to be spare-parts-stock to be supplied to Dealer order.

Your response is brilliant and as you will see by the image attached very accurate. The Jaguar assigned HSN is indeed BZ695!!


I was sure it was a C5 but I think you are correct in stating that it is a C3.
Thank-you for the seminar on Type C heads!

Perhaps you may know this already but there is a terrific book on WYF called MELTDOWN which, with great research richly details the rise during the second World War of WYF, to its ultimate demise under British Leyland c2004.
In its post-war heyday it was a huge facility, operating ten foundries south of Leeds in the UK, in approximately 18 acres.
Meltdown is ISBN: 0-9548828-1-4

A HSN of BZ695 - pretty well as expected based on other detail, so nothing to change my best-guesstimate of a circa January 1957 date Head was manufactured/completed and held in stock for Spare Parts supply.


Thanks Stephen,
Nope, hadn’t heard of that book MELTDOWN.
Will have to start looking and see if I can locate a copy for sale, if anyone has any clues.
But yet another BL casualty.


For your records, here are the numbers from S818919 DN:

Cylinder head: G 8931-8S
Part number: C7707-1
Casting sequence number: RHE 488
Head sequence number: BM787

Thanks Gary,

Can you double check the Casting Sequence Number whether RHE488 or possibly RHE448 as per your advice back in 2013


Roger Payne



Hi Roger,
Difficult for me to believe, but apparently I was more confused back in 2013 than I am nowadays.
It’s really RHE488.
Sorry for the incorrect information.

fI asked on the XK engine list recently but got no answer so will try here:

Are the threads for the round alloy Allen key plugs in the valley the same as the later hexagonal steel plugs? Do the round plugs come out or just mangle the socket? Does anyone know a source?

E kuy

I measure the thread as 7/8-14 UNF.
There is a copper washer under them.
I bought a hex key socket from Menards so I could get a long handle on it.
Two came out ok, one was mangled.
I would recommend a propane torch on them.

BTW I recently learned the source of that word mangled.
A mangle is the thing with two rollers and a crank handle for wringing the water out of clothes in a laundry. Dickens mentions it in Nicholas Nickleby published 1839. Obviously you wouldn’t want to get your hand in a mangle, hence mangled.

Cant argue with a photo Gary, many thanks.
Clearly I recorded CSN number incorrectly back in 2013 :slight_smile:


Thanks. Are they interchangeable with the hex steel ones?

I mangled many mangles as a schoolboy. I had a summer job demolishing houses for salvage. The boss ran a workshop of about ten home-made hand looms, weaving rugs out of fabric waste. The mangle gears were fitted to the looms, being used to advance the roll of finished rug and to tighten the strings.

In the early 18 hunfreds “ has your mother sold her mangle” was a phrase in popular use in London. Little known fact courtesy of QI.
If you ever meet a time traveller from then, you may find this a useful conversation starter

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Or conversation finisher, as it was an insult. It meant either, “Your clothes are dirty or wrinkled and need the attention of a laundress.” or “Your mother is a washerwoman.” i.e. the lowest social level. :grin:

Having lived a large part of my life in South London in the early seventies, I’d say it was a comment on sartorial efficiency. Similar to ‘do you call that shirt ironed?’ Implying, of course, that it isn’t. A bit of English irony (oops, pun unintentional)