I have owned many vintage XK 140s, 150s, e types, and saloons. I have searched far and wide prior to posting here! I apologize if this topic has been covered, I did not find it.
Quite apart from the engine number stamped to the front of the head which appears on the vin plate - Many-most XK engine heads from 1958-1967 have a letter welded to the center of the spark plug valley usually “N” or “A” – AND they have a rectangular plate welded to the rear of the valley with - usually - two letters and three numbers.
I cannot find info that explains what these ID letters and numbers reference. I’ve read that the single letter in the spark plug valley references straight port, or not, cylinder heads but I have no reliable dating for these letters. I have found no reference at all for the two letters/three numbers rectangular plate in the rear of the same spark plug valley.
I’m confused because I’ve seen many ‘matching numbers’ 3.4 liter XK150S models with both and “A” and an “N” in the valley - and I’ve also seen e types with the same. Including a later 4.2 liter e type engines with an “A”. What does that letter signify?
What do the two letter/three number plates at the rear of the cylinder head signify?
I’m looking at purchasing an expensive XK150S and want to know if these identifiers can help confirm the authenticity and date of the engine in the car.
“Welded” is not really the correct term. The raised letter in the valley and raised plinth at the rear are part of the original casting. They look that way because on the wooden foundry molding pattern the letter is a separate piece screwed on.
I have only seen a large raised letter C in the middle of the valley, which indicated the head was the C-type head casting, as opposed to the standard head which had no letter. I don’t recall the later B-type and straight port heads having such a letter.
The hand stamped numbers in either the middle or the rear of the valley are production sequence numbers. We believe they were stamped on by the foundry that made the rough castings for production record keeping. Research into the translation of those numbers is still ongoing, but suggests that they began with A1 through A999, then B1 - B999, and so on. My 1951 XK120 has the number E5 stamped between plugs 3 & 4. An unknown year Mark VII head in my shed has BA271 at the rear.
New head types such as the C, B and straight port heads started back at the beginning with possibly A1 or AA1. My C-type head from 1956 has BC444 at the rear of the valley.
By accumulating lots of these production numbers and associating them with engine assembly serial numbers found at the front of the head, we may eventually be able to make guesses as to the month and year of production of these heads.
You can identify the type of head by the raised casting part number found on the bottom, usually on the carb side. By comparing this with the serial number on the front, you may be able to determine if an incorrect head has been restamped.
I just checked five heads. Only the 65 E with hex core plugs has a raised letter central in the valley (an N about 1/2"). The Fifties Mk1 with round alloy Allen Head plugs and the Seventies S2-S3 XJ heads with round pressed-in core plugs have nothing.
Hi rob - yes semantics are everything! Not stamped - not molded during the manufacturing but added as separate tags as you pointed out.
A quick google search of “e type cylinder head numbers” will show pictures of a 150S head, several e type heads, all with both N and A letters in the plug valley of the head. My cars are stored elsewhere or I’d go take pics. What’s odd to me is that these letters appear on xk150S heads AND 4.2 E-type heads from series one cars. Doesn’t seem to be a chronological or even engine size marking since they appear on 3.4, 3.8, and 4.2 sized engines. So maybe a second foundry marking to designate …? Anyway - it’s curious and no one seems to quite have an answer! Thank you for your help.
I’m happy to add my cars to your registry after Christmas
Just to be sure we are all understanding; I did not mean the letter was screwed onto the cylinder head. I mean the letter was screwed onto the molding pattern in the foundry, i.e the tooling from which heads are made. That is why you sometimes see the image of what look like screw heads around these markings.
Google didn’t yield me much. I found one image of a head on ebay with what looks like a molded letter N between plugs 3 and 4.
There might be another letter but I can’t make it out.
Here is the molded letter C on my C-type head. Notice the faint image of nail head shapes where the sand was pressed around the nails.
The letter C is well known to indicate a C-type head.
Here is the stamped foundry production sequence mark BC444 on my C head.
Here is the stamped foundry production sequence mark E5 on my standard A-type XK120 head.
We are collecting reports of the stamped numbers to try to establish whether they can tell us anything. At this time month/year dating is only speculative.
I am inclined to suspect the letters A and N may indicate particular mold pattern sets used by the foundry; since they were making hundreds of heads per week, they probably had several sets of molds patterns, and changed them whenever a set needed repairs.
If there was more than one foundry under contract with Jaguar to make heads, it may also be a mark signifying which foundry made the head.
You might check on the E-type forum to see if those folks have ever investigated these letters A and N.
Hi again - thank you for the updates. I also posted to the e type forum and they sent me back here!
They are such prominent markings it is surprising no one seems to have an answer.
Your conjecture that these are foundry markings may be spot on - since I have seen both “N” and “A” on e types and on Xk150S heads - suggesting there is no dating significance to those marks.
