Cylinder Head w/no Engine Number

I’ve recently bought a C-type replica that has a 3.4 MK2 engine bottom end, with an unmarked cylinder head. Would this be an XJ head? It does protrude past the rear edge of the cylinder block so I am assuming it is a later head.

Thanks for any replies,

IIRC, heads were no longer stamped with the number after the late 60s.

Edit. I was wrong my ‘71 does not have the engine number in the head. It is down on the rear engine flange.

My memory dims on this, so it may have been in the early 70s that this happened.

Hey Mark, neither of the 72 S1 XJ heads or the 73 head I have in the shop are numbered behind the timing gear case as per earlier cars.

Is your head drilled for air-injection?

~Mike SBCC

Where would I look for this? It does have a row of Allen screws in the head valley
on the exhaust side I’ve never seen before.

The allen screws up on the top like that are probably to stop the cam follower buckets from moving - like the stake-down kit but external. Kind of strange.

Air injection holes would be down on the floor on the exhaust side near the plugs. They’d also be filled with something like allen head plugs and very obvious.

Back in the day, I did that a lot: it was fast and easy to do, and quite effective.

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Attached are two pictures showing the Series III XJ6 cylinder head, with its six air injection ports circled in red, that I put on my 1969 E-Type FHC for a few years when I had problems with the original cylibder head.

I found suitable brass plugs at a local hardware store but I have seen several other methods of sealing up those air injection ports.


Same solution I used on my Jeep engine.

Ah thanks for the pic. No my head doesn’t have holes like that. I guess I’ll have a better idea of what I have when I pull the cam covers off to check valve clearances.

Thanks for the replies. You fellows are very helpful.


One other thing Mark,
All of my S1 XJ6 heads have screw in core plugs (green circle location). My S3 XJ heads are all like yours with a core plug pressed in.

Also the pads or features shown in the yellow circle don’t exist in any of the heads in my collection - all 4.2. I wonder if the head on your car is from a later rest-of-world 3.4? North America got the air-injection but others did not.


Hi Mike, my car was sold as a turn-key complete car from Heritage in England in1986. So I assume they used what was available locally then. The bottom end is MK2.

That would explain your later style core-plugs and no air injection on what would be an emission era head for US cars. Drive it to the next club meeting so I can ogle it in person :wink:

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My E-Type has had the engine from an S2 XJ, installed long before I bought it. No number on the head, the only number is stamped on left edge of the bellhousing. There was no air pump until the S3 XJ, so there are no ports for that, either. I also have the grub screw mod to retain the tappets. This was a popular mod in the previous century.

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I resemble that crack.


Who doesn’t?

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Hey Mike, I took it to donuts Saturday morning. I’ll bring it to the meeting next month if you’re going. The weather has been a crapshoot lately.



Ah…my favorite MG!


Sorry Michael but unfortunately for us the US spec XJ6’s did indeed have air pumps beginning in 1972 with engine 7L42595. So 2 years of S1 and all the S2 and S3.