S3 valve stem seals

Hello everyone,

In the parts manual I see valve stem seals on the inlet valves, but my1985 model does not have any installed.

Do you have more information on this ?

Thank you.

It most definitely has, from 1968 on. Have they become hard?

The valve stem seals, on the inlet valves only(!), prevents oil being sucked into the engine via the valve stem, Rui. They are important, though not critical for running the engine - and should be there.

They were either omitted during a PO overhaul, or have (somewhat unlikely) disintegrated. They are worth while reinstalling - though, arguably, not urgent…

xj6 85 Sov Europe (UK/NZ)

Frank , David, many thanks.

I took.off inlet valve #2 and no trace of valve stam seal .
I can see in an engraving on he thead casting and a small Jaguar plate on the block, that engine was replaced by a Jaguar remanufactured unit one year after production in 1986.

Could we have found an explanation for the black sludge found on the valve train, oil.being sucked and coming off with exhaust fumes through the exhaust valve stams? After 75 thousand miles ?


The seal was introduced to avoid oil and fumes being drawn into the engine and not the other way; engines without the seals don’t sludge up this badly, so I believe that these are not related, but could be wrong!

Yes, but if some oil gets draged in through the inlet guides then a tiny burned bit could also get out through the exhaust guides. Enough to get the valve train black dirty after 80k miles ? Just a thought .
In any case the car did not consume oil .

It’s a bit of a long shot, Rui, but then; 75000 miles is a long time…:slight_smile:

Any long term effects of omitting the valve seals are not know, But constant intrusion of oil onto hot valve stems, accentuated over time by inevitable valve guide wear, may certainly cause build-up of residue - and possible inlet valves sticking.

There is valve overlap - which, theoretically, may cause transfer of dirty oil/residue between in and out valves to the head. It is just a bit of a long shot as an explanation of sludge build up in the head; combustion residue is not supposed to enter the head.

But if it does; the build-up residue will stay throughout oil changes. And, unlike the residue caused by piston blow-by, oil intrusion caused by missing stem seals will not necessarily contaminate the sump oil more than normal.

Whatever the train of events, when I said ‘not urgent’ I did not visualise driving 70000 miles without stem oil seals. Moral of the story; fit the stem seals…

xj6 85 Sov Europe (UK/NZ)

Long shot maybe indeed, but the only one so far that could explain the black carbon film over the valve train, mainly on the exhaust side . Note that intake valves are clean as new , no signs of sludge , it’s the exhaust side that built some, possibly because after 75k miles of accumulating very small amounts of burnt oil in the exhaust valve stems - but for a very long time . Maybe …

Now as for a factory rebuilt engine not having stem seals , that’s another mistery . I wonder if that can still qualify under the warranty :smile:

Do you know the full history of the engine? I would expect an engine without inlet valve stem seals to drink oil. When my car was 25 years old and 60,000 miles the original seals were shot and the car drank oil at such a rate that after one 800 mile trip I had to put 2.5 litres back in.

You call that drinking?

I have the car for 23 years now, but I drove it maybe only 20.000 km over the two decades . I don’t recall signs of oil consumption even on a longer trip I made , around 1200 km . And I don’t remember having to add oil between yearly oil changes - but again I didn’t drive it much . Back in the late 90s I had a BMW 320i E30, that consumed 1l/ 1000 km since new .

The main reasons for fitting seals on the inlet valve only was that inlet valves suck into the cylinders, Rui - while outlets blow out of the engine. Inevitably some combustion products will pass the valve stems into the valve train, but the very high outlet valve stems get too hot (very hot indeed!) for practical sealing. So over 75 000 there will be a build-up of whatever on the exhaust side as well…

Of course 75 000 over 23 years would unlikely require added oil between regular oil changes - but the engine might still may have used more oil than normal due to stem seals missing…

As an aside; if the oil is filled to the full mark on the dipstick, the xk engine will burn off the top pint or two very quickly indeed…

I doubt if ‘the’ cause of your troubles can be divined to perfection, but warranty or not; do fit the inlet stem seals - at least it will not hurt…:slight_smile:

xj6 85 Sov Europe UK/NZ)

That is very clear Frank , the seals are already on my SNG -Holland purchasing list, currently blocked as they are waiting for the headgaskets to arrive .

Now you only have to drive another 75000 miles to test theories, Rui…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

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