Series 3 cylinder head

[Norton]

Hello.
Two cylinder heads have come up for sale here in Norway, seller claim they will fit E type S3. He quotes part no. C32256 / C32257. Photo shows C32257 clearly. Other one a bit unclear, P32256K. As far as I found out theese numbers are for XJS pre HE. Are XJS heads identical to E type heads? If not, what are the differences?
Any modification needed?

Rgds Harald.

[MarekH]

V12 cylinder heads came in two varieties.

1/ Flat head. These had flat lower face and were designed to work with dished pistons to achieve the desired compression ratio. The spark plugs point more or less vertically upwards.

2/ HE heads. These had recessed pockets in the heads and were designed to work with flat headed pistons to achieve the desired compression ration. The spark plugs holes are angled towards the centre of the "V".

A pre-HE head from an XJS is going to be a flat head, so will be compatible with the pistons already fitted in an E-type block.

kind regards
Marek

[Norton]

Hi.
Thanks Marek. Theese are flat. If I understand you right, they will fit a standard S3.

Rgds Harald.

[Norton]

Hi.
Ended up bying the heads and they look ok. But there is always something. Upon closer examination there are some stripped threads and needs recoiling.

One in the head for the stud to attach the camshaft block. 5/16 18tpi. At first I assumed it is BSF / withworth thread, but could it be UNC?

Two threads in the camshaft block to attach rocker cower. 1/4 20 tpi. Same question, BSF or UNC?
See photo.

Last, there are fitted valve stem seals to the exhaust valves. It is adviseable to just leave them in place or should they be removed?

Thanks, Harald.

[MarekH]

A copy of the Parts Manual from the donor car will tell you which bolts are needed.

Valve stem seals are there to prevent oil seeping down the valve stems. Jaguar didn't put any on the inlet as that will just be ingested into the cylinders and burnt off whereas the exhaust oil will leak out into the tailpipe.

kind regards
Marek

[lowact]

UNC.
The original (flat) heads used unified imperial threads. The later (dished HE) heads used metric threads.

[Norton]

Thank you for information.
Unfortunately I don’t know anything about donor car.

Valve seals leaves me a little puzelled.
Both SNG Barrat and SCparts lists valve stem seals for inlet valves only in their «parts lists».
I have an engine parts list, e type S3. Says nothing about valve stem seals. ( photo )

I have little experience with theese engines. What are recommended, no stem seals, on the inlet / outlet or both?

Thanks, rgds Harald.

[lowact]

You are correct, I have deleted the misinformation from my earlier reply. I blame the fog of time since I considered fitting exhaust valve seals.
Some cars have seals on inlet and exhaust valves, Jaguar V12 didn’t, had seals on the inlets only. On inlets the differential pressure tendency is to compress the seal onto the stem thereby assisting the sealing. With exhaust valve seals it is the opposite, the differential pressure acts to expand the seal and reduce the sealing. For this reason exhaust valve seals (on other cars) generally have a garter spring that ensures the seal despite the pressure. I recollect an article about retrofitting such seals to the V12; due to the larger diameter of the seals with garter-springs there was a clearance issue with the valve springs.

[MarekH]

The aftermarket valve stem seals are not necessarily wider, but they are taller. This is because there is no way to attach them other than with a spring collar, as there is no indented groove on the inlet side for a seal to sit on. (One spring collar sits on the base and second collar clamps the stem.) One consequence of being taller is that if a high lift cam is fitted, the valve stem can push down far enough to touch the top of the seal... with catastrophic consequences.

I have low profile Teflon seals if people want them.

kind regards
Marek

[Norton]

Hi.
Thanks for information.
Have taken out 3 exhaust valves ( and 1 inlet valve ) to have a look and find out whats in there. The stem seals on exh valves look identical to them on the inlet. Definitely no garter spring.

Should I leave seals on exhaust valve were they are, or it is better to get rid of them? Will they do any harm / any useful if left in place?

Do anyone know the nominal height of head? Just to get an idea of how much have been skimmed off during the years.

Marek, the teflon seals you have do they have garter springs and are of standard height / diameter?

Thanks.
Harald.

[MarekH]

The rubber valve stem seals only stay seated because they clip onto a groove on the top of the valve guides, so no groove, no way to hold the seal unless the seal has a spring loaded retaining collar. This is why they originally only appeared on one set of guides - the others don't have the groove. I look to have confused my inlets and outlets earlier.

Teflon seals have retaining spring collars rather than working by clipping onto a retaining groove.

The only reason to worry about how much may have been taken off of a flat head is that this makes the timing chain "too long" by 4x the amount taken off (assuming both heads skimmed the same amount). At some point earlier in the chain's life cycle, the timing chain tensioner will push the chain towards the centreline of the engine and eventually metal to metal contact will occur. There is no performance gain/loss as the combustion chamber size is unchanged.

Aftermarket teflon seals are available in lots of sizes and mine are the right size for the v12. You can have them for standard camshafts or also for higher lift camshafts. They have spring collars so can go on both inlet and exhaust valves.

kind regards
Marek

[Norton]

Hi, thanks.
Living and learning.
Yes the head is flat, it was the timing chain I was thinking about.
Marek, your teflon seals sounds interesting. Sending you a PM.

Rgds Harald.