Do I need seals and if I do which side exhaust and/or intake?
If I need them on the intake side are there seals that will fit the
old valve guides w/o grooves on the top?
Wes,
Your engine was not originally fitted with valve stem seals. The
information I have indicates that Jaguar began using valve stem seals on the
4.2 in 1969. The spring retainers, keepers and spring seats were changed and
I believe you have to convert over to use the seals. Valve stem seals are
usually used on the intake side because there is less than atmospheric
pressure (vacuum) in the intake manifold, especially on the over run, which
can suck oil into the intake port and into the combustion chamber. One test
for a car with worn guides or seals is to accelerate down
hill in top gear and release the throttle while looking in the mirror. If
blue smoke comes out the exhaust, the engine is sucking oil past the guides.
I converted to the new style parts when I rebuilt the engine in my 3.8S
eight years ago. I also used the short style tappets, but I’m not sure that
is required, maybe someone else knows. I also have bronze guides and I have
not had a problem and the oil consumption in negligible. I do not know of a
seal that will fit the old guides. I hope this helps.
Drag racers use bronze because they can fit the stems very tight and hold
better valve seal for max power. Smokey Yunick’s book on building Chevy road
racing engines specifies cast iron as “the perfect guide material” .Gran
Turismo Jaguar’s catalog says the same thing- saying they rebuild worn out
bronze guides frequently. I am unaware of any regular car manufacturer using
bronze.
Hello Doug
"Bronze" guides is a over simplification, just as "steel" means many
different things. The quality and longevity varies with the alloy content
and the engine design. As for regular car manufactures using “bronze” valve
guides, I have personal experience with two, Porsche and BMW, who along with
Honda, are arguably the finest engine builders. I believe there are others.
Porsche used copper alloy guides in their 911 engine until 1977 when they
switched to silicon-bronze guides which reputedly can last over 300,000
miles. I can’t verify this, I don’t get to drive mine that often. BMW uses
copper alloy guides in their M10 engine (among others) which seem to last
around 75,000 miles ( 4 cars, 300,000 + miles). I’ve had “bronze” guides in
my XK 3.8 engine for eight years and it doesn’t burn oil through the guides,
so I think it depends alot on the guide material, the installation, and the
engine temperatures. As to Smokey Yunick and the Chevy, I think its apples
and oranges, there’s not much in common with the XK. I’ve read some of his
stuff and he seems to have a political axe to grind. Sometimes I find it
helps to consider the motivations of the writer when reading “history” books
or catalogs.
The machinist who is going thru the head on my 1971 4.2 motor for
my 61 mk. 2 wants to put stem seals on intake and exhaust valves.
He says thats how it was when he took the head apart. Any thoughts?–
pete
phoenix az., United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
In reply to a message from old goat sent Thu 2 May 2013:
pete,
There were no exhaust valve seals fitted to the XK engine.
This is a clue that means a PO was in there messing about
and doing non factory mods. If your machinist does not know
this, you should start getting concerned about valve stem
height, retainer recess and shim range. Did you specify a
valve stem height or give him the valve to cam spec ? Which
type of seal was used and are the valve guides the original
iron or aftermarket bronze ? If the seats have been cut
before and he does not understand the valvetrain, you may
wind up outside shim range or with shims that hit the
retainers.
Paul–
The original message included these comments:
The machinist who is going thru the head on my 1971 4.2 motor for
my 61 mk. 2 wants to put stem seals on intake and exhaust valves.
He says thats how it was when he took the head apart. Any thoughts?
In reply to a message from old goat sent Thu 2 May 2013:
The valve hardware and guides are set up for seals on the
exhaust side, but unnecessary. I’ve seen late model heads
with seals on both intake and exhaust, but they may have
been added later. I guess it’s up to you, and it won’t hurt.
Joel–
ex jag, '66 E-type S1 4.2, '56 XK140dhc, '97 XJ-6
Denison, TX, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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So what is the final advice? I take it that the early XK engines did not have Valve Stem Seals to start off with. Today’s engines have. If you want the Valve Stem Seals, I guess you have to replace the original Valve Guides with those that accept the Seal. Now the question is, what material? Steel or Bronze. My experience has been to change them to Bronze.
A simple response would be appreciated. Thank you
Yes, bronze. But a simple response may not tell you all you need to know …
I’ve just had the job done on my XK120 head and have learned a few things in the process. The springs are the same but the spring seats, collars and keepers need to be replaced with the later versions… The valve guides that take seals are longer to accept the seals. If you don’t replace the original hardware the seals will get wrecked the first time the engine is turned over. This is a pic of the two versions, with the older on the right of the newer:
The later collars are 0.100” shorter. You need seals only on the intake side so should be able to reuse the older versions on the exhaust side so long as the new longer guide doesn’t interfere. Engines from MY 1969 were fitted with the newer style on both sides.
