Mark 2 engine numbers

Mark 2 3.8 liter engine number range

A bit cryptic is there a question here?

My cylinder head LE 1448 9 has been seriously damaged.
I inherited LC 9707 9 many years ago.
Are they interchangeable?

More than likely even 4.2 heads can be fitted to the smaller engine capacities (with a bit of fettling)

Thank you for your speedy response.
This particular car has 198k miles under its belt and I have tried to keep it as original as possible. I would like to limit the deviations from standard to a minimum. What are the specific differences between these heads?

Short answer, yes. 3.8 Mk2 engines start at LA, go through to at least LE. Should be identical.

I was hoping that might be the case.
Is there a factory log that still exists that identifies these changes?

Not that I am aware, but lots of people here know which permutations of engines were used in the various models. For example, all Mk2s used the B Type head, as did S Type; 240’s, some, if not all 340’s ( I think there is debate over that) used the straight port head (SPH), all 4.2’s used SPH etc. Any doubt, just ask here. All heads are interchangeable, sometimes requiring mods, other times not, sometimes worthwhile, other times not.
Basically, there are 6 types of head, chronologically being A Type, C Type, B Type, SPH for 3.4\3.8, SPH for 4.2 and Big Valve SPH for S3 XJ6.
The first three are similar with regard to inlet port spacing ( all exhaust ports are the same) but differ in regard to valve size , valve seat angle and port size. The same inlet manifolds will fit all of these.
The 3.4\3.8 SPH was fitted to XK150S, 3.8 E Type and 3.8 Mk10, and will bolt directly to any 2.4, 3.4 or 3.8 block. Port spacing is different, so the correct manifold, either twin or triple will be required. In a Mk2, triples present clearance issues, but both need mods to connect to the radiator.
The later 4.2 head, always SPH, has extra coolant passages at the rear, so if used with a smaller block, these need to be blanked off. Ditto, the S3 head which has larger inlet valves, but same port spacing.
In a nutshell, others may elaborate or correct me. :slightly_smiling_face:

I wouldn’t pretend to know enough to correct this post Kevin.

Thanks Paul, very generous.

I think you will find all 240 and 340 do indeed have a Straight Port Head, and these early SPHs will fit onto all 1950s, and 1960s 3.4 and 3.8 blocks. Similarly the SPHs as fitted to earlier 420s will also fit. However from about 1968/9 onwards the 4.2 block received an extended water jacket at rear of block, and thus also on the SPHs now fitted on later 420s, 4.2 XJ6 and 420G, thus they will not fit onto a 3.4 nor 3.8 1960s block as fitted to Mark 2, S type, 3.8 and 4.2 E types and Mark 10s. That is unless your occupation dresses you in a blue and white striped apron. The various SPCs will give you exact engine number demarcation points, but regardless the quick clue is the head gasket to be used. Does your head gasket properly seat on the 3.4 or 3.8 block, and if so does it also properly align all the water jacket holes on the underside of your propsed SPH you wish to use. The biggest difficulty is having an inlet manifold that suits the SPH, as the inlet ports are different to that fitted to a Mark 2 B type head.

This is why I mentioned there is some debate about whether all 340’s received the SPH. I don’t know for sure one way or the other. Not sure butchery is involved in fitting the later head; I think the rear coolant holes can be blanked successfully without resorting to that.

Of course a later SPH with its extended rear and water jacket will physically drop over the studs onto the block without any issues. My comment was re ‘Thermodynamic Butchery’. The whole purpose of the extended water-jacket in both block and head, was to cope better with the additional thermal load of the regular air-conditioning fitment, by providing improved coolant flow at the rear of the head and block. If you blank of the rear coolant passages at the rear of the extended head, with the head also blanking off the rear coolant passages at the rear of the block, you have zero coolant flow where it was needed, thus my ‘Thermodynamic Butchery’

Sorry Roger, I didn’t mean to sound rude.
Don’t the later SPH’s have 4 coolant holes at the rear and you only blank of the two rearmost, so still normal coolant flow to the rear of the “small blocks” through the other two?

Both are off of a 3.8 litre engine so no problems good idea is to overhaul valves and tappet shims whilst you have it on the bench
I have made up a couple of stands which helps working on the head and enclose a photo
They are located through the stud holes


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I had a numbers matching 340 and it did not have a straight port head. It did when I sold it because of severe corrosion in the original head.
The intake with water connections was tricky combination to get it to work out.

Also heres part of the head listings for the original poster…

Thanks Tim, that’s interesting considering others insist they all had SPHs.
I assume, but don’t know for sure, that the radiator might be different for those fitted with SPH., as the inlet manifold \thermostat setup seems hard to fit to a standard Mk2 radiator.
As an aside, the performance figures for a 340 road test are very close to those of a 3.8, so perhaps that one had an SPH.

I also note the head listing shows some 240s had a non-SPH although other details are missing. Ditto, hp figures absent for 340 and 340 3.8 SPH models. Also note some are listed as painted silver or not painted. My early S1 XJ has remnants of silver paint on the head that are distinguishable from the bare alloy.