XK 120 SE Type Head


My name is Peter - I’ve been a member here for a short.

An XK120 has been a dream car of mine for many years and I’ve finally bought one.

It is an steel car XK120SE DHC, that was delivered new in USA in 1953, I bought it in September 2022 in Austria.

I look forward to sharing more information with you, and I thank you in advance for tolerating the questions I may have as I get to know the car.

And here is my first question:

The car corresponds to the attached certificate, but it has a different engine head, see photos.

Is it a XK140SE C-type head from 1954 or 1955 or not?
Warm Regards

Peter Boril
Kladno, Czech Republic

Yes, serial number G6785-8S with casting part number C7707 and the prominent C in the valley is certainly a C-type head from an XK140, although it is the 5785th XK140 engine to come off the production line, so it is probably from 1956 or 57.

Hi Peter:

Welcome to the Forum. I was interested to see the data on your heritage certificate as my car, also a 1953 DHC, was built about 3 weeks after yours in July (677577).


Thank you very much for your reply.

Hi Chris,

unfortunately I only have the data from the certificate from Jaguar. I bought the car through a company that serviced it for the last owner in Austria. Now I want to write to this owner to find out any more details.


You might also want to check the engine block serial number, which is located on the right hand side where the oil filter head is attached.

You are right - the numbers on the label and on the block are different. The number on the block and on the head is identical - G6785-8S. I think, that engine prefix G = XK140. Is it possible to find out details about the engine from this data? Thank you.

Yes, a G serial number is certainly from an XK140.
G engines began with G1001 so yours is number 5785 out of approximately 9000 XK140 engines built, allowing for a few spares. Using Phil Porter’s data in “Original XK” puts it at approximately January 1956 production.
The suffix numeral 8 indicates that it has 8:1 compression ratio, which is determined by the crowned pistons.
The suffix letter S indicates that it has the C head, valves and high lift cams.

Peter, welcome to the forum. Could you upload a photo showing the front of the inlet manifold? I’m interested in whether the engine retains the XK120 manifold or whether the XK140 manifold is present. (It’s more difficult to make a neat upper hose connection to the XK120 radiator when the XK140 inlet manifold is used.)

And another question. Are my carbs H6 type?

You have the XK140 inlet manifold adapted to the XK120 alloy thermostat housing which is bolted to the XK120 radiator. The temperature bulb fitting on the XK120 thermostat housing has been blocked-off, and the bypass fitting on the bottom of the housing must have also been blocked off.

The bypass hose on the XK140 inlet manifold appears to be routed an XK140 water pump. This indicates the thermostat location is on the XK140 inlet manifold. Similarly, the temperature bulb must be attached to the inlet manifold. All in all, this appears to be a tidy adaptation. Yes, the car retains the H6 carbs which were originally supplied to both the XK120 and XK140.

One other question. Does the radiator fan have 6 blades (XK120) or 8 blades (XK140)?

The radiator fan has 8 blades.

Very nice. The 8 blade fan is about 2.5 inches larger in diameter compared to the 6 blade XK120 fan. This should improve the cooling capacity in summer driving.

The cooling is solved as follows:

1 Like

Hello - I’m asking for advice again. What is that threaded hole in the lower part of the transmission. Is it far back - is it for attachment or is there a missing some stopper? Thank you for your help.Peter

someone has put a synchro gearbox in the car and they original had a coils spring a spigot at this point
the whole rear gearbox mount has been modified altered etc

Thank you very much for your reply.
Looks like I bought a puzzle - Jaguar XK120SE chassis and body July 1953, engine from XK140SE January 1956. And transmission ??? Does anyone know what car it comes from? I recognized that it looked different from the original, but nothing more. Anyway, 2nd gear is quite difficult to shift there, and I don’t have a problem with gearboxes without synchronization. 3nd and 4rd gears are OK.

I wonder if it might be from an E-Type.
This is the tailcase for the 3.8 E.

Look on the left side up near the top rear corner, see if there is a number there like this.

I don’t know if it will help for identification - I can’t take better photos.

I’m about 50% sure it’s an E-Type box, but with an XK120 top cover.
There may be a serial number here.

You may need a flashlight and a mirror to see it.
An E-Type gearbox serial number will begin with the letters EB or EJ.

Your chassis mounting bracket has been modified to make the box fit.