[xj] Spark plug woe

This morning on the drive work, the 6 cylinder Daimler was running
rough. Not all the time, but enough to cause concern.

So at coffee break I pulled the spark plugs one at a time. The 4th
one to come out, instead of being clean, looked like this:

http://www.jag-lovers.org/v.htm?1208341924

approx 1 cm of the insulator has broken off.

I’ve got to drive it home this evening (9 miles) and can then have
a go at seeing if the the ceramic shards are still in the
combustion space, if there’s any compression left, and possibly at
fitting a replacement plug.

Has anyone else experienced this sort of failure of a plug
electrode insulator? Anyone care to speculate on the likely
collateral damage or the cause?–
al mclean '93 XJS 4.0 - '84 4.2 Daimler - '84 DD6
Telford, United Kingdom
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In reply to a message from almcl sent Wed 16 Apr 2008:

…approx 1 cm of the insulator has broken off. Anyone care to
speculate on the likely collateral damage or the cause?..I’ve got
to drive it home this evening (9 miles) and can then have a go at
seeing if the the ceramic shards are still in the combustion
space…

Detonation. The broken piece has almost certainly been blown out
through the exhaust, with little if any ‘‘collateral’’ damage…–
1977 XJ6C , 1988 XJ-S H&E
skaneateles, ny, United States
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Al,
Your concern is for the wrong problem, I believe you are looking at a
secondary failure. Look close at the picture you gave us and see that there
is eutectic aluminum residue coating the end of the electrodes. If this
picture is accurate I do believe you have burnt a piston. A bore scope will
tell the tale if you have one. You will find the top of the piston starting
to burn away at the 3-9 o’clock position as viewed from the side of the
engine.
What ignition coil are you using? What type of driving does this car
get generally?
Driving this car any further would not be a good idea, at this point the
piston may be able to be replaced without boring the block but that would
only be if you have caught this early enough.
Keep us posted on your findings
Best Regards
Gregory McCord
“Scotlander”
90 VDP Majestic
00 XJ8
94 XJ-40
63 MK II 3.8----- Original Message -----
From: “almcl” al.mclean@blueyonder.co.uk
To: xj@jag-lovers.org
Sent: Wednesday, April 16, 2008 6:41 AM
Subject: [xj] Spark plug woe

This morning on the drive work, the 6 cylinder Daimler was running
rough. Not all the time, but enough to cause concern.

So at coffee break I pulled the spark plugs one at a time. The 4th
one to come out, instead of being clean, looked like this:

http://www.jag-lovers.org/v.htm?1208341924

approx 1 cm of the insulator has broken off.

I’ve got to drive it home this evening (9 miles) and can then have
a go at seeing if the the ceramic shards are still in the
combustion space, if there’s any compression left, and possibly at
fitting a replacement plug.

Has anyone else experienced this sort of failure of a plug
electrode insulator? Anyone care to speculate on the likely
collateral damage or the cause?

al mclean '93 XJS 4.0 - '84 4.2 Daimler - '84 DD6
Telford, United Kingdom

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almcl wrote:

This morning on the drive work, the 6 cylinder Daimler was running
rough. Not all the time, but enough to cause concern.

So at coffee break I pulled the spark plugs one at a time. The 4th
one to come out, instead of being clean, looked like this:

http://www.jag-lovers.org/v.htm?1208341924

approx 1 cm of the insulator has broken off.

I’ve got to drive it home this evening (9 miles) and can then have
a go at seeing if the the ceramic shards are still in the
combustion space, if there’s any compression left, and possibly at
fitting a replacement plug.

Has anyone else experienced this sort of failure of a plug
electrode insulator? Anyone care to speculate on the likely
collateral damage or the cause?

Yes to the first, and more than once, Al - and ‘nothing’ in my case to
the second…

Which may be just dumb luck, but I never found any traces of it - being
brittle they seemed to have been chewed up and spat out through the
exhaust. But if you find bits they should certainly be removed - it’s
certainly abrasive stuff. Beyond that it’s not really much to be done
without some serious dismantling…

This cannot be a singular occurrence - and the manufacturers may have
thought of it in the composition. Which may be the cause in the first
place, or a manufacturing fault, or some careless handling - in short;
shit happens…? :slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)===================================================
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In reply to a message from almcl sent Wed 16 Apr 2008:

Al,
Just out of curiosity, was that a Champion plug (R12NY ?) ?
How about your coil - just kidding, please !!–
The original message included these comments:

Has anyone else experienced this sort of failure of a plug
electrode insulator? Anyone care to speculate on the likely
collateral damage or the cause?

al mclean '93 XJS 4.0 - '84 4.2 Daimler - '84 DD6
Telford, United Kingdom


Jim Legge '85 SIII XJ '96 LR Disco
Washington, DC, United States
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In reply to a message from James Legge sent Wed 16 Apr 2008:

Al:

The end of the worls hasn’t come yet!!

I suspect it may have been cracked on setting the gap and failed
later leading to rough running. Hope it wasn’t you that set the gap.

There is a lot of action going on in multiple repeats of the
combustion process at a very rapid rate. I doubt that the bits
survived for very long. The liklihood of just dropping out of the
plug in one piece is beyond remote. A Frank says, the remnants are
long gone.

Similarly, I doubt that there was any piece large enough to damage
a piston. Just think, strong healthy aluminum versus crumbled
ceramic! who wins! I don’t know if these are forged pistons or
cast, but both are certainly stronger than ceramic, especialy
ceramic that has failed.

Yea, if looking in with a borescope is feasible, why not? Were it
mine, it would get a new set of plugs, carefully gapped and soldier
on.

Good Luck

Carl–
The original message included these comments:

The original message included these comments:

Has anyone else experienced this sort of failure of a plug
electrode insulator? Anyone care to speculate on the likely
collateral damage or the cause?


Carl Hutchins
Walnut Creek, California, United States
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In reply to a message from cadjag sent Wed 16 Apr 2008:

Well, we got home alright!

I stopped to pick up a spark plug or two on the way.

For interest I checked the peak firing voltage of each cylinder in
turn and not surprisingly the dodgy plug was well down on the rest
(9kV for the good ones, 5kV for the broken one.)

I pulled the plug and checked the compression - 150 psi, which is
what it was 18 months ago, so, as you all told me - no signs of
damage there. I couldn’t see much down the plug hole (and don’t
have access to a boroscope) but the little that was visible looked
like the standard piston crown black gunk. So I fitted the new
plug, fired up and checked the firing voltage which was back up to
9kV. The idle was smooth although I haven’t been for a test drive
yet.

For info, the plug was a Unipart GSP 151, gapped at 35 thou and
fitted as part of a set, by me, about six months ago. The coil is
a nearly new Lucas DLB 198 and the car is mostly used to take me to
and from work (9 mile single journey) and for errands around town
although it does get the occasional longer blast.

I’ll report any other findings after a bit more running.

Thanks for all your replies.–
al mclean '93 XJS 4.0 - '84 4.2 Daimler - '84 DD6
Telford, United Kingdom
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Ditto here. Had one do that in our Sprite decades ago. The pistons & valves
didn’t care a bit. Maybe the car following behind got hit by the tip though,
since the muffler is straight through.
;]
As for “eutectic Aluminum”, the term is misapplied, since a eutectic substance
is by definition a mixture of two or more materials that minimizes some
parameter, such as melting point. Aluminum & Silicon are often mixed in such
proportions for castings. Electrical solder of 37% Lead & 63% Tin is a
eutectic mix. And, for a eutectic: “all the constituents crystallize
simultaneously at this temperature from molten liquid solution”

The stuff on the plug in the pic looks like carpet fuzz!–
Alex
79xj6L SII (BRG + wires)
86xj6 SIII (Black)
61 Sprite MkII (Red)
Menlo Park, Calif.

345 DeSoto wrote:

Detonation. The broken piece has almost certainly been blown out
through the exhaust, with little if any ‘‘collateral’’ damage…

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Hi Alex, good to see you are still trying to keep me in line. :wink:
Eutectic aluminum is the exact correct use of the term in this case,
eutectic refers to a “state” of constituents. The tip of the center
electrode and the top of the ground look exactly like eutectic aluminum
deposits in my opinion.
The alloy used in pistons of this era were heavy in copper. This fact
creates a very even euctic film when heated past the euctic boundary then
cooled. I’ll bet that film can be easily scraped off of the electrodes and
left in a pile on the table where a drop of base will react with it quite
handily proving it to be aluminum.
Best to know now than to allow it to continue further and score the
cylinder wall beyond repair. A quick bore scope will tell the tale.

Best Regards
Gregory McCord
90 VDP Majestic
00 XJ8
94 XJ-40
63 MK II 3.8----- Original Message -----
From: “Cannara” cannara@sbcglobal.net
To: xj@jag-lovers.org
Sent: Wednesday, April 16, 2008 2:54 PM
Subject: Re: [xj] Spark plug woe

And, for a eutectic: "all the constituents crystallize

simultaneously at this temperature from molten liquid solution"

The stuff on the plug in the pic looks like carpet fuzz!

Alex
79xj6L SII (BRG + wires)
86xj6 SIII (Black)
61 Sprite MkII (Red)
Menlo Park, Calif.

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Greg, I was simply pointing out that “eutectic” is meaningless when used as a
modifier for a single-element substance. There’s no such thing as “eutectic
aluminum”, “eutectic silver”… There are only eutectic mixtures of multiple
elements.

As far as engine damage, I’ll bet there’s none detectable.–
Alex
79xj6L SII (BRG + wires)
86xj6 SIII (Black)
61 Sprite MkII (Red)
Menlo Park, Calif.

kcscotlander@sbcglobal.net wrote:

Hi Alex, good to see you are still trying to keep me in line. :wink:
Eutectic aluminum is the exact correct use of the term in this case,
eutectic refers to a “state” of constituents. The tip of the center
electrode and the top of the ground look exactly like eutectic aluminum
deposits in my opinion.
The alloy used in pistons of this era were heavy in copper. This
fact creates a very even euctic film when heated past the euctic
boundary then cooled. I’ll bet that film can be easily scraped off of
the electrodes and left in a pile on the table where a drop of base will
react with it quite handily proving it to be aluminum.
Best to know now than to allow it to continue further and score the
cylinder wall beyond repair. A quick bore scope will tell the tale.

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In reply to a message from Cannara sent Thu 17 Apr 2008:

Here we go again…–
1977 XJ6C , 1988 XJ-S H&E
skaneateles, ny, United States
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Pessimist!
;]–
Alex
79xj6L SII (BRG + wires)
86xj6 SIII (Black)
61 Sprite MkII (Red)
Menlo Park, Calif.

345 DeSoto wrote:

In reply to a message from Cannara sent Thu 17 Apr 2008:

Here we go again…

1977 XJ6C , 1988 XJ-S H&E
skaneateles, ny, United States

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In reply to a message from Cannara sent Thu 17 Apr 2008:

Probably ‘realist’ Alex.

Greg, Alex, to the extent this is a highly technical point it will
bore the pants off some, and interest a few others. I also know
there are some who like a good ‘dust-up’ and find it entertaining.
C’est la vie. The forum can’t please everyone all the time and
people can just skip the topic or delete emails.

For my part, being a bit of a knowledge junkie I’ll quite happily
read to absorb some new technical minutiae and possibly get beyond
my basic understanding of eutectic alloys.

However - and you know this is coming - keep it civil please. And
remember that I am the sole arbiter of what constitutes ‘civil’ so
I’d appreciate if you could make my job really easy by staying on
topic and keeping it technical, not personal.

Or you can just let it drop.

Pete
XJ Admin–
The original message included these comments:

Pessimist!


66 2+2, 78 RAM D-type replica
Cambridge, United Kingdom
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In reply to a message from 345 DeSoto sent Thu 17 Apr 2008:

Maybe best to not go down the pedant route and forget about the
facts of the plug failing and there being some sort of aluminium
looking crap on it.
I agree with Greg that the plug is most probably a secondary
failure, just swapping it and driving on may not be a good idea.
Comp test seems ok, I’d at the minimum do a mixture and timing
check. Did the other plugs have a good colour ?
Maybe the ‘‘occasional blast’’, as previously discussed elsewhere,
was a major contributing factor ?

Dave–
The original message included these comments:

Here we go again…


Dave Collishaw '79 S2 Daimler Sov '92 xj40
Peterborough, United Kingdom
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In reply to a message from sparx sent Thu 17 Apr 2008:

The other plugs all looked fine, a1though no 6 was a little paler
than the others. The one that failed was no 3.

Last MoT the mixture was 3.14%CO at idle and the HC were 298ppm,
and according to my gas tester the CO hasn’t changed since.

Haven’t checked the timing for a while, good thought, I’ll have a
look this evening.–
The original message included these comments:

Comp test seems ok, I’d at the minimum do a mixture and timing
check. Did the other plugs have a good colour ?


al mclean '93 XJS 4.0 - '84 4.2 Daimler - '84 DD6
Telford, United Kingdom
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Hi Peter,
This is an interesting case of a very early failure diagnostic. I
certainly hope the owner will head the warning he has been given by the
spark plug failure and have a look at the top of that piston.
A quick factoid on aluminum; This metal does not exist in pure form in
nature in any quantity without being refined. In it’s pure refined form it
is pretty much useless for industry as it is extremely soft and malleable.
Industry adds many different metals to it to form the alloy we use everyday.
When aluminum melts and re-solidifies, there is a very easily recognized
characteristic color and texture signature. In it’s eutectic state it forms
a sheeting appearance and usually adhering to everything that can tolerate
the temperature. Alloying aluminum is done at the molecular level and at
high heat. The microstructure of this metal is a lattice appearance. The
spaces between the lattice are filled with other metal molecules to give it
its strength. These metals must be close to the same mechanical properties
of the aluminum such as melting point and molecular size. When aluminum
becomes hot enough to become liquid, there is a fine temperature range when
the constituent metals are still solid. It is this temperature range that
produces the effect we might be seeing in this spark plug example. The pure
metal aluminum has been allowed to flow leaving the alloying metals behind,
most likely still solid but now loose and causing damage to the rings and
cylinder walls.
Detonation most likely broke the ceramic insulator. That is the bad
news as detonation is a killer in a hemispherical combustion chamber, much
more so than in a conventional wedge type combustion chamber. Detonation is
caused by a localized hot spot usually on the piston dome and caused by
heavy carbon deposits superheating a small spot on the least quenched
surface areas like the 3-9 o’clock positions.
The damage is that now the piston is missing some material that directly
provides cooling to the rest of the piston dome through conduction. This
spot that is now deficient of material will continue to collect carbon and
become a hot spot which will continue to melt away more alloy until a
catastrophic failure occurs.
My procedure would be to try and find a bore scope and inspect the
piston dome for eutectic erosion damage. If found that piston would need to
be replaced. If caught soon enough, a unit repair can be made without a
complete overhaul. This looks like a really good candidate for an early
diagnosis.
Best Regards,
Gregory McCord
“Scotlander”
90 VDP Majestic
00 XJ8
94 XJ-40
63 MK II 3.8----- Original Message -----
From: “PeterCrespin” jag@thewritersbureau.com
To: xj@jag-lovers.org
Sent: Thursday, April 17, 2008 2:21 AM
Subject: Re: [xj] Spark plug woe

In reply to a message from Cannara sent Thu 17 Apr 2008:

For my part, being a bit of a knowledge junkie I’ll quite happily
read to absorb some new technical minutiae and possibly get beyond
my basic understanding of eutectic alloys.

Pete
XJ Admin

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If we’re happy “absorb some new technical minutiae”, then, Greg, we need to
stick to facts, so others aren’t misled…

  1. “The damage is that now the piston” – you and we have no such evidence.
    Those of us who’ve had similar evenst over the years have yet to find any
    evidence. Your words are misleading.

  2. “Industry adds many different metals to it to form the alloy we use
    everyday” – there are various Aluminum alloys “we use every day”, depending
    on application.

  3. “In it’s eutectic state” – why you continue misusing “eutectic” is a
    mystery. All you have to do is look it up to get the correct meaning and use.

  4. “Alloying aluminum is done at the molecular level” – all true metal alloys
    are at the atomic (molecular) level, because the differences in atom sizes is
    being exploited to gain advantages, like strength. Aluminum isn’t uniquely so
    made.

  5. “These [alloying] metals must be close to the same mechanical properties of
    the aluminum such as melting point and molecular size” – untrue. If you want
    a easily-available, factual definition…

    ‘…most alloys do not have a single melting point. Instead, they have a
    melting range in which the material is a mixture of solid and liquid
    phases. The temperature at which melting begins is called the solidus
    and the temperature when melting is complete is called the liquidus.
    However, for most alloys there is a particular proportion of constituents
    which give them a single melting point or (rarely) two. This is called the
    alloy’s eutectic mixture.’

And, to boot, we even get a proper meaning for “eutectic”!

  1. “…pure metal aluminum has been allowed to flow leaving the alloying
    metals behind, most likely still solid but now loose and causing damage to the
    rings and cylinder walls.” – again, absolutely no physical evidence, yet, or
    from our past experiences.

  2. Finally, the dreaded “eutectic erosion damage” – occurs under extreme,
    concentrated heating, as from a plasma/arc device. Electrical contacts in
    switches that repeatedly interrupt large currents experience this because
    they’re relatively small. A large piston, sustaining a few detonation events
    that break a sparkplug doesn’t.

I may be wrong, and Al’s piston may look like a Mordor monster’s complexion,
but the statements below need the corrections mentioned.–
Alex
79xj6L SII (BRG + wires)
86xj6 SIII (Black)
61 Sprite MkII (Red)
Menlo Park, Calif.

kcscotlander@sbcglobal.net wrote:

Hi Peter,
This is an interesting case of a very early failure diagnostic. I
certainly hope the owner will head the warning he has been given by the
spark plug failure and have a look at the top of that piston.
A quick factoid on aluminum; This metal does not exist in pure form
in nature in any quantity without being refined. In it’s pure refined
form it is pretty much useless for industry as it is extremely soft and
malleable. Industry adds many different metals to it to form the alloy
we use everyday. When aluminum melts and re-solidifies, there is a very
easily recognized characteristic color and texture signature. In it’s
eutectic state it forms a sheeting appearance and usually adhering to
everything that can tolerate the temperature. Alloying aluminum is done
at the molecular level and at high heat. The microstructure of this
metal is a lattice appearance. The spaces between the lattice are
filled with other metal molecules to give it its strength. These metals
must be close to the same mechanical properties of the aluminum such as
melting point and molecular size. When aluminum becomes hot enough to
become liquid, there is a fine temperature range when the constituent
metals are still solid. It is this temperature range that produces the
effect we might be seeing in this spark plug example. The pure metal
aluminum has been allowed to flow leaving the alloying metals behind,
most likely still solid but now loose and causing damage to the rings
and cylinder walls.
Detonation most likely broke the ceramic insulator. That is the bad
news as detonation is a killer in a hemispherical combustion chamber,
much more so than in a conventional wedge type combustion chamber.
Detonation is caused by a localized hot spot usually on the piston dome
and caused by heavy carbon deposits superheating a small spot on the
least quenched surface areas like the 3-9 o’clock positions.
The damage is that now the piston is missing some material that
directly provides cooling to the rest of the piston dome through
conduction. This spot that is now deficient of material will continue
to collect carbon and become a hot spot which will continue to melt away
more alloy until a catastrophic failure occurs.
My procedure would be to try and find a bore scope and inspect the
piston dome for eutectic erosion damage. If found that piston would
need to be replaced. If caught soon enough, a unit repair can be made
without a complete overhaul. This looks like a really good candidate
for an early diagnosis.
Best Regards,
Gregory McCord

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In reply to a message from Cannara sent Thu 17 Apr 2008:

All:

Perhaps this thread, if it continues should go to piston metalurgy.

I recall my son, a very good performance machinst, discussing
clearances for hypereutectic pistons. The gist was that the
hypereutectics should be set with less clearnace than others.

So, I ‘‘Googled’’. I found a nice concise article in Wikipedia.

In essence. Aluminum alloy pistons contain trace amounts of
magnesium, copper and nickel. Silicon is adding ranging from 16% to
19% in the alloy refered to as hypereutectic.

The genesis is in seeking to make a cleaner engine. Hypoeutectic,
low silicone alloys expand slower than the iron of the block.
thusly clearances must accomodate this resulting in a ‘‘loose’’ fit.
The engine runs dirty, at least until warm up.

Hypereutectic expands less and as such the pistons can be set at
a ‘‘tighter’’ fit and run cleaner.

They are subject to detonation!

I recommend any that are interested to go to the article. I may be
able to provide it off line as I did save it.

Carl–
Carl Hutchins
Walnut Creek, California, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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In reply to a message from cadjag sent Thu 17 Apr 2008:

So Carl, hypoeutectic has low silicon and hypereutectic has high
silicon, right ? Kinda like blood sugar ? So high silicon is more
subject to detonation ? I’m sure this will come up on Jeopardy.
Wow, the things we learn on JagLovers ! ;^) The cherry blossoms
are in full bloom and the Pope is here. It doesn’t get much better
than that !–
The original message included these comments:

I recall my son, a very good performance machinst, discussing
clearances for hypereutectic pistons. The gist was that the
hypereutectics should be set with less clearnace than others.
In essence. Aluminum alloy pistons contain trace amounts of
magnesium, copper and nickel. Silicon is adding ranging from 16% to
19% in the alloy refered to as hypereutectic.
The genesis is in seeking to make a cleaner engine. Hypoeutectic,
low silicone alloys expand slower than the iron of the block.
thusly clearances must accomodate this resulting in a ‘‘loose’’ fit.
The engine runs dirty, at least until warm up.
Hypereutectic expands less and as such the pistons can be set at


Jim Legge '85 SIII XJ '96 LR Disco
Washington, DC, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

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The archives and FAQ will answer many queries on the XJ series…
FAQs: http://www.jag-lovers.org/xjlovers/xjfaq/index.html
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In reply to a message from James Legge sent Thu 17 Apr 2008:

Me, I’d change the plugs for maybe a different
manufacturer, Check the ignition timing & keep driving &
let someone else worry about the chemistry,failure
analysis, or whatever!–
The original message included these comments:

silicon, right ? Kinda like blood sugar ? So high silicon is more
subject to detonation ? I’m sure this will come up on Jeopardy.
Wow, the things we learn on JagLovers ! ;^) The cherry blossoms


Keith Turner '79 XJ6 based Aristocat,
Swansea, United Kingdom
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

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