Which Head Should I use

I have my 4.2 torn down and the head has more corrosion that I am comfortable with in the water jackets. I started looking for a replacement head and I ended up buying 3 of them.

The challenge is none of them are off a 4.2 E type but the list is as follows

3.8 E type head that has had some performance work done such as polishing, believe new seats and stems, additional oil holes drilled in the bottom valley of the cam trays, and the water jackets machined out so they are one large slot in lieu of two small slots.

2.4 head from a MK2. Does not seem to be a straight port. And not sure it would be a good fit.

4.2 head from a 420. This Head is bone stock.

More information is needed. What type of 4.2 engine do you have and what are your plans for it. The more information the better your responses will be.

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You could have your original head weld repaired too.

If your original head was in useable condition, apart from the corrosion, repairing that could cost you less than diving into another head that’s an unknown entity.



I don’t know this for sure, but I thought a 1967-1968 420 (and 420G) cylinder head would be the same as a 1967-1968 E-type cylinder head. Only the inlet and exhaust manifolds are diffrent, right? Can you compare how your 4.2L E-type inlet manifold would fit? I think all coolant passages should line up correctly, no?


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  1. Repair your original head.
  2. Use the 420 head; it is essentially the same.
  3. Sell the 3.8 head; it is worth good money
  4. Take the 2.4 head to the scrap dealer. It isn’t.

I should note I have a S1 and the engine production date is 1966. It does not have the additional water passages on the rear of the block or head.

I do not plan on making it a performance engine for racing. Just street use.

It seems the 4.2 head looks the same but it seems too good to be true.

Any lead on a repair shop? You can PM if you want.

Send it to Coventry West: @Dick_Maury can help you with details.

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This head is scrap unless you plug all the added oil drain holes. If the oil drains away the cams run dry at each startup and destroy the cams and buckets.

The 420 head might be the same if a 420G. The inlet port position will be the difference. The 3.8 head will work but you will need to remove the two plugs on the inlet side for water circulation. The water jackets were not machined out. They were made that way on the 3.8. The 4.2 split them into two sections. The 2.4 with non straight ports will not work.

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Ok. Thanks. If your block and head are the original numbers matching ones for your car you are best to repair the original head or at least save and store it carefully for the future. It is my understanding that the 420 head is completely interchangeable with your original head but you would need to confirm that it is actually a straight port head and that your carbs and manifold fit correctly and that it is in fact in excellent condition and does not need work. If it needs work you are probably farther ahead to just have the original redone. We always hear nothing but good things about Coventry West for that kind of work.

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Hi, The 420 head is the same as an E type. Different intake and exhaust manifolds from the E type.
I have two Series 1 E types and a 420 sedan.


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Most machine shops who deal with race engines are capable of weld repairing aluminum heads. However, my biggest concern with a Jag head would be the DOHC configuration, so I think you’d want to go with a shop that has Jag experience to ensure they don’t build a twist into the head.

Classic Jaguar in Texas often post some impressive weld repairs in their blog. Others here have already suggested Coventry West, so they would be worth a call too.