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.
Thank you for any help.
Jeff