[xj] re: smoking and no plug fouling

Having read about this probelm now for a while I thought that I put my Five
cents in…
This sounds like a classic case of leaking exhaust valve seals or excessive
exhaust valve stem wear. Symtoms.
Oil smoke - blue from exhaust but no plug fouling as the oil is entering the
“burning” cycle after the cylinder. Excessive smoke on hard accel after
coasting on engine de-accel.
Follow this procedure if you want to test for this probelm.
Drive down a long hill, make sure that it is steep enough and long enough to
allow about 30 seconds of travel at 50mph with your foot off the gas.
Now the idea is, you are trying to get the engine to develop excessive
vaccum/backpressure in the exhaust manifolds, this is achieved by engine
braking. This will draw oil down the stems and into the exhaust port to be
burnt in the manifolds.
To do this on an auto you use 2ND or 3RD in an manuel.
Make sure that there is no or little traffic as it means one less thing to
concentrate on.
With two people in the car travel down the hill at about 50 mph , take your
foot off the gas and let the engine try to slow the car down through engine
braking. After about 20-30 seconds of doing this without touching any
pedals. Nail the accelerator to the floor whilst having the passenger look
out the rear window, if you see a big cloud of smoke when the pedal is
floored then that is probably valve stem seals or stem wear.
Other signs can be if you get a lot of smoke in the mornings, as overnight
the oil in the top of the motor leaks down the stems and is burnt on
start-up if it runs rough it is inlet, if not exhaust.
Note : this test can pick-up both inlet and exhaust wear and should be used
as a guide -hope it helps
greig

At 10:42 PM 11/9/99 +1300, you wrote:

Having read about this probelm now for a while I thought that I put my Five
cents in…
This sounds like a classic case of leaking exhaust valve seals or excessive
exhaust valve stem wear. Symtoms.

Most engines do not have seals on the exhaust valves, including the Jag
4.2. Excessive wear on valve stems will cause oil consumption usually only
on the intake valves. This is because there is a vacuum on the intake
stroke (pulling oil down the intake stem), and pressure on the exhaust
stroke (pushing any oil back up the stem).

Excessive exhaust valve stem wear could produce smoke at startup, as the
oil might seep down the stems when the engine is not running.

Oil smoke - blue from exhaust but no plug fouling as the oil is entering the
“burning” cycle after the cylinder.

Not neccesarily. Burning oil may not foul plugs noticeably. A two stroke
“burns” injected (or mixed) oil all the time and does not foul the plugs
(if properly tuned). It does not smoke once warmed up because 2-cycle oil
is specially formulated to minimize smoking.

Excessive smoke on hard accel after

coasting on engine de-accel.
Follow this procedure if you want to test for this probelm.
Drive down a long hill, make sure that it is steep enough and long enough to
allow about 30 seconds of travel at 50mph with your foot off the gas.
Now the idea is, you are trying to get the engine to develop excessive
vaccum/backpressure in the exhaust manifolds, this is achieved by engine
braking. This will draw oil down the stems and into the exhaust port to be
burnt in the manifolds.

Correct, but the maximum vacuum draws down the intake valve stems only.
There is no increase(or decrease) back pressure in the exhaust.

Just my .02.

greig

Mike
87 VDP>

Agree. And, with transverse engines, if an end valve is leaky, and the car is
parked on a sideways slope, the engine (head) can be tilted enough to foul
just the plug on the low side, and just by parking for a few minutes.

Alex
79xj6

Michael Aiken wrote:

[clip]>

Most engines do not have seals on the exhaust valves, including the Jag
4.2. Excessive wear on valve stems will cause oil consumption usually only
on the intake valves. This is because there is a vacuum on the intake
stroke (pulling oil down the intake stem), and pressure on the exhaust
stroke (pushing any oil back up the stem).

Excessive exhaust valve stem wear could produce smoke at startup, as the
oil might seep down the stems when the engine is not running.

Oil smoke - blue from exhaust but no plug fouling as the oil is entering the
“burning” cycle after the cylinder.

Not neccesarily. Burning oil may not foul plugs noticeably. A two stroke
“burns” injected (or mixed) oil all the time and does not foul the plugs
(if properly tuned). It does not smoke once warmed up because 2-cycle oil
is specially formulated to minimize smoking.

Excessive smoke on hard accel after

coasting on engine de-accel.
Follow this procedure if you want to test for this probelm.
Drive down a long hill, make sure that it is steep enough and long enough to
allow about 30 seconds of travel at 50mph with your foot off the gas.
Now the idea is, you are trying to get the engine to develop excessive
vaccum/backpressure in the exhaust manifolds, this is achieved by engine
braking. This will draw oil down the stems and into the exhaust port to be
burnt in the manifolds.

Correct, but the maximum vacuum draws down the intake valve stems only.
There is no increase(or decrease) back pressure in the exhaust.

Just my .02.

greig

Mike
87 VDP

L&G,

It is my experience that Jaguar did/does/do not install valve seals on
the exhaust valves…intake only. As always, I could be
wrong…again…happened in 1963 and I’m still trying to get over it.
JW

Lisa and Greig wrote:>

Having read about this probelm now for a while I thought that I put my Five
cents in…
This sounds like a classic case of leaking exhaust valve seals or excessive
exhaust valve stem wear. Symtoms.
Oil smoke - blue from exhaust but no plug fouling as the oil is entering the
“burning” cycle after the cylinder. Excessive smoke on hard accel after
coasting on engine de-accel.
Follow this procedure if you want to test for this probelm.
Drive down a long hill, make sure that it is steep enough and long enough to
allow about 30 seconds of travel at 50mph with your foot off the gas.
Now the idea is, you are trying to get the engine to develop excessive
vaccum/backpressure in the exhaust manifolds, this is achieved by engine
braking. This will draw oil down the stems and into the exhaust port to be
burnt in the manifolds.
To do this on an auto you use 2ND or 3RD in an manuel.
Make sure that there is no or little traffic as it means one less thing to
concentrate on.
With two people in the car travel down the hill at about 50 mph , take your
foot off the gas and let the engine try to slow the car down through engine
braking. After about 20-30 seconds of doing this without touching any
pedals. Nail the accelerator to the floor whilst having the passenger look
out the rear window, if you see a big cloud of smoke when the pedal is
floored then that is probably valve stem seals or stem wear.
Other signs can be if you get a lot of smoke in the mornings, as overnight
the oil in the top of the motor leaks down the stems and is burnt on
start-up if it runs rough it is inlet, if not exhaust.
Note : this test can pick-up both inlet and exhaust wear and should be used
as a guide -hope it helps
greig

There are indeed only oil seals on the inlet valves.
I suspect my actual valve stems and guides are the problem.

JV
XJ6 SIII> L&G,

It is my experience that Jaguar did/does/do not install valve seals on
the exhaust valves…intake only. As always, I could be
wrong…again…happened in 1963 and I’m still trying to get over it.
JW

Lisa and Greig wrote:

Having read about this probelm now for a while I thought that I put my Five
cents in…
This sounds like a classic case of leaking exhaust valve seals or excessive
exhaust valve stem wear. Symtoms.
Oil smoke - blue from exhaust but no plug fouling as the oil is entering the
“burning” cycle after the cylinder. Excessive smoke on hard accel after
coasting on engine de-accel.
Follow this procedure if you want to test for this probelm.
Drive down a long hill, make sure that it is steep enough and long enough to
allow about 30 seconds of travel at 50mph with your foot off the gas.
Now the idea is, you are trying to get the engine to develop excessive
vaccum/backpressure in the exhaust manifolds, this is achieved by engine
braking. This will draw oil down the stems and into the exhaust port to be
burnt in the manifolds.
To do this on an auto you use 2ND or 3RD in an manuel.
Make sure that there is no or little traffic as it means one less thing to
concentrate on.
With two people in the car travel down the hill at about 50 mph , take your
foot off the gas and let the engine try to slow the car down through engine
braking. After about 20-30 seconds of doing this without touching any
pedals. Nail the accelerator to the floor whilst having the passenger look
out the rear window, if you see a big cloud of smoke when the pedal is
floored then that is probably valve stem seals or stem wear.
Other signs can be if you get a lot of smoke in the mornings, as overnight
the oil in the top of the motor leaks down the stems and is burnt on
start-up if it runs rough it is inlet, if not exhaust.
Note : this test can pick-up both inlet and exhaust wear and should be used
as a guide -hope it helps
greig

I want to thank all who posted this thread’s messages to the list, rather
than to the sender only, because the symptoms confirmed a suspicion I had
about my 120 – looks like leaky valve guides there, too.

“Mark 1” Mark Stephenson
1952 XK120 Roadster #673129 (w/XK140 engine and C head)
1958 3.4 Litre Saloon / 1984 XJ6 4.2L / 1985 XJ6 VDP
Jaguar Club of Central Arizona (USA) – www.cableone.net/jcca