[xk-engine] Porcelain Coating on Exhaust Manifolds

My manifolds came back after porcelain coating by Prairie
Auto Porcelain in Faribault Minnesota.

http://www.jag-lovers.org/v.htm?1462386643

Tom Sparrow at Prairie had these recommendations:
Start out with short runs for a couple minutes at idle.
Then maybe 3-7 minutes then 8-13 minutes.
Always run at idle for at least 7-8 minutes to get porcelain
into the 640 plus degree range prior to driving.
Then your main expansion takes place during idling and when
take off occurs not a lot of heat rise is left.
Don’t run above 2500 rpm for the first 1000 miles.
Any rain or sweat off your forehead at 600 plus will
fracture the porcelain.
It is preferable to have slow general expansion rather than
localized heating which would yield very non-uniform expansion.
Heat management is crucial to maintaining nicely fired
porcelain.
Sometimes, even following best practices doesn’t save the
finish. The heat history of the iron has a lot to do with
the expansion characteristics of each piece. When iron gets
old and crystallized it expands much further in less time
than younger/quality iron. Replacing an old original with
better iron is sometimes the answer to ongoing issues.
Carbs running too lean is the most common porcelain killer.

I used McMaster-Carr #90575A312 studs made of 316 stainless
steel with 93439A635 bronze nuts, stainless steel lock
washers and Anti-Seize.–
XK120 FHC, Mark V saloon, XJ12L Series II, S-Type 3.0
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In reply to a message from Rob Reilly sent Thu 5 May 2016:

Interesting but ultimately futile IMO.

I went so far as to bake new ones at progressively longer
intervals and higher temps in an oven, before even putting
on a car. Then I did idle curing and gradually worked up the
revs pretty much as Tom’s advice suggests. Of course, Jaguar
would have gone out of business telling people not to use
more than 2500 rpm for a thousand miles, but I did my best.

Nevertheless, on the first long hard run of an hour the
crazing started. The carbs were if anything slightly rich.
With the best will in the world, once everything reaches
steady-state at revs of about 3000 rpm or higher for long
stretches of highway, the differential expansion at the
points of greatest curvature and flame confluence is too
great to support full porcelain adhesion.

I think the best cure is to readjust our expectations and
attitude so that anyone whose manifolds are NOT cracked
feels like a wuss and goes out to drive their car harder. A
pristine manifold, like a clean tailpipe or totally tar-less
wheel-arch, should be a source of embarrassment, not
frustration.–
The original message included these comments:

Don’t run above 2500 rpm for the first 1000 miles.
It is preferable to have slow general expansion rather than
localized heating which would yield very non-uniform expansion.
Sometimes, even following best practices doesn’t save the
finish. The heat history of the iron has a lot to do with


66 ‘UberLynx’ D, 70 FHC, 79 S2 XJ12L, 97 XJ6L
Gaithersburg, Maryland, United States
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I gotta go with Peter C. on this…
I’ve been on the XK & XK-Engine lists since 1999 (Rob R was
on them when they were still using stone tablets ;-} )… The
Porcelain issue has been cussed and discussed till hell won’t have
it… BUT, in the end, the “Heat Gods” win and cause the Porcelain
to surrender it’s grip on the Jag’s cast-iron exhaust manifolds…
Now, that said, if after shelling-out nearly $500 for some “bling”,
it makes perfect sense to “try” to extend that “new look” for as
long as possible… If Tom’s instructions forestall the inevitable for
several thousands of miles or years (and I don’t mean “trailer
queen years”, but “Driver Years”), then it might just be worth the
effort to follow Tom’s “Break-In” instructions… However, if the
porcelain is going to “pop” after the first thousand miles of
driving, then romp the hell out of your Jag and enjoy yourself…
I do recall one XK owner describing his “solution” to keeping
“perfect” porcelain manifolds… he had two sets… One “show
quality” that he installed when the Jag was judged, the second
set was used the other 99.999% of the time… In other words,
the “show set” never experienced ANY heat!!
I have a “new” set of nice black shiny porcelain exhaust
manifolds still in their shipping box… I might follow the “show/
driver” swap idea… but then, I might just drive the hell outta the
Jag and just not worry about it, I’m not going to live long enough
to restore my 120, again… (there are bets out that I might not live
long enough to finish the current restoration!! C’est la Vie,
C’est La Mort, C’est La Guerre, C’est Toute L’enchilada!!)
Charles #677556----- Original Message -----
From: “PeterCrespin”

Interesting but ultimately futile IMO.

I went so far as to bake new ones at progressively longer
intervals and higher temps in an oven, before even putting
on a car. Then I did idle curing and gradually worked up the
revs pretty much as Tom’s advice suggests. Of course, Jaguar
would have gone out of business telling people not to use
more than 2500 rpm for a thousand miles, but I did my best.

Nevertheless, on the first long hard run of an hour the
crazing started. The carbs were if anything slightly rich.
With the best will in the world, once everything reaches
steady-state at revs of about 3000 rpm or higher for long
stretches of highway, the differential expansion at the
points of greatest curvature and flame confluence is too
great to support full porcelain adhesion.

I think the best cure is to readjust our expectations and
attitude so that anyone whose manifolds are NOT cracked
feels like a wuss and goes out to drive their car harder. A
pristine manifold, like a clean tailpipe or totally tar-less
wheel-arch, should be a source of embarrassment, not
frustration.

66 ‘UberLynx’ D, 70 FHC, 79 S2 XJ12L, 97 XJ6L
Gaithersburg, Maryland, United States

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In reply to a message from Rob Reilly sent Thu 5 May 2016:

For what it’s worth, I know of several Iowa Jags where the
porcelain work from Prairie Auto has held up beautifully.
But I know of more cases where it has not.

Years ago Walt Osborn told me that he had found someone who
could make the porcelain stay on the manifolds. However,
that individual died and took the process to the grave.
After that happened, Walt discontinued offering a porcelain
service for the exhaust manifolds.

So I suspect that someday someone will re-discover how to
consistently apply porcelain for long-term durability.–
Mike Balch
Iowa, United States
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In reply to a message from Mike Balch sent Thu 5 May 2016:

At least everyone will get to know their name, as they are
bound to get the Nobel Prize for re-writing the laws of
physics and physical chemistry. It’s not a lost art, the
porcelain flaked off the cars in period too. there’s nothing
to ‘re-discover’

You don’t have to be Einstein to see that the porcelain
never flakes first on the head or pipe flanges where the
section is thickest, mass is heaviest, temperatures are
lowest. You just need eyes. Even where there is no manifold
and the metal is the same thickness all the way (like on
motorbike exhaust pipes) you can still see the clear heat
gradient from head to pipe and the hotspot where the chrome
blues because the flame is forced to turn downwards as it
strikes the outside of the top bend.

Since differential expansion is related to heat and hotspots
are where the flaking occurs first, the rest of the story is
obvious. Keep the heat down and keep the porcelain intact.
Drive the car enthusiastically, or even moderately but for
prolonged periods, and the porcelain flakes off. QED, end of
story.

Pete–
The original message included these comments:

Years ago Walt Osborn told me that he had found someone who
could make the porcelain stay on the manifolds. However,
So I suspect that someday someone will re-discover how to
consistently apply porcelain for long-term durability.


66 ‘UberLynx’ D, 70 FHC, 79 S2 XJ12L, 97 XJ6L
Gaithersburg, Maryland, United States
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In reply to a message from PeterCrespin sent Thu 5 May 2016:

I have no experience with porcelain, but I have used ceramic
insulating coatings on industrial equipment and piping that
operates at high temperature. It’s very effective, even in thin
coatings. I wonder if an internal coating of this would be of
benefit?–
The original message included these comments:

never flakes first on the head or pipe flanges where the
section is thickest, mass is heaviest, temperatures are
lowest. You just need eyes. Even where there is no manifold
and the metal is the same thickness all the way (like on


Mike Spoelker
Louisville,Kentucky, United States
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In reply to a message from Mike S sent Tue 10 May 2016:

The discussion of this subject on the XK forum led me to
believe that internal coating would indeed be of benefit in
conducting more heat away to the head pipes and beyond.

Prairie is able to do the inside, where Independence
Porcelain said they could not, so that was one reason I went
with Prairie. The other reason was that he quoted the
highest price for doing the outside, plus an additional
charge for doing the inside, so I figured he was probably
the best. For something like this I didn’t like to go with
the lowest bidder.

I’ve gone through the recommended warmup steps and had one
driving run. So far everything is good, no cracks. I’ll
report again after I put on a few hundred miles.–
XK120 FHC, Mark V saloon, XJ12L Series II, S-Type 3.0
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In reply to a message from Rob Reilly sent Fri 13 May 2016:

It’s not distance covered - they’d probably last forever
below 200-2500 rpm for an hour every trip. But after a few
longer trips at 3500+ , different story–
66 ‘UberLynx’ D, 70 FHC, 79 S2 XJ12L, 97 XJ6L
Gaithersburg, Maryland, United States
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In reply to a message from PeterCrespin sent Sat 14 May 2016:

I’m happy with them but if its such a sore subject I’m sorry
I mentioned it.–
XK120 FHC, Mark V saloon, XJ12L Series II, S-Type 3.0
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In reply to a message from Rob Reilly sent Sat 14 May 2016:

Not a sore subject at all, except for my personal
disappointments. The last pair I bought I went to
extraordinary lengths to normalise them/stress-relieve
thrm and work my way up the temp scale etc.

Everything seemed good and I really thought I’d found the
Holy Grail. Thankfully the exact details have escaped my
memory, but I probably did do 500-1000 miles running a
non-lean set of triple SUs. All seemed good, including the
odd fast burst and I was happy. Sadly, I was merely
delaying the inevitable, as the first long fast trip saw
the cracking and flaking set in at the hot spots and
eventually spread. There were areas that never came
detached - mostly around the flanges - but the after 6-12
months of proper driving (even with 5-speed low rev
gearing) the manifolds I took great care of looked as bad
as any others.

I think a lightly-used car never held at medium/highish
revs might see them survive longer and a show car maybe
indefinitely, but I could never hold a Jag on a leash like
that. To each their own, however. I now use flat black
paint.–
66 ‘UberLynx’ D, 70 FHC, 79 S2 XJ12L, 97 XJ6L
Gaithersburg, Maryland, United States
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In reply to a message from PeterCrespin sent Mon 16 May 2016:

Pete
I’ve had a set of SNG manifolds on the C-engine we saw
together ( and I bought). I have at >3000 miles on them
(they were on my original XK-20 motor for a year). Every
year I do two trips of around with sustained 3500-4000 rpm
for several hours (80-90mph cruising speed for 300-400
miles).

No cracking but the finish is not as glossy as original.
If they last five/10k miles years before they flake,
that’s acceptable durability.

John–
John
Boston, MA, United States
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In reply to a message from John sent Mon 16 May 2016:

I’m impressed. I crazed two sets of theirs. Of course that
was on a full-size 4.2 that breathes a little deeper than
a weeny lil’ 3.4 :slight_smile:

John Merring died a few weeks ago BTW.

Pete–
66 ‘UberLynx’ D, 70 FHC, 79 S2 XJ12L, 97 XJ6L
Gaithersburg, Maryland, United States
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In reply to a message from PeterCrespin sent Mon 16 May 2016:

Pete, are you sure you aren’t running lean?
I use a wide band O2 sensor to check/adjust my carbs.
What I discovered is the the best idle setting resulted in
a lean high rpm mixture. So, now I run rich at idle (yes
it loads up the plugs). I have a set of new needles that
should reverse this pattern, but am just too lazy to
instal them. I wonder if this is helping my manifolds
last.–
John
Boston, MA, United States
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In reply to a message from PeterCrespin sent Mon 16 May 2016:

Sorry to hear about John M.
For those of you who didn’t know him, he was the epitome
of Jaguar enthusiasm, and one of the earliest Jag club
members anywhere in the nation. he will be missed.–
John
Boston, MA, United States
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In reply to a message from John sent Mon 16 May 2016:

Thid was some years ago John. The teo E-types were stolen.
Plug colour said not lean and carbs were refurbed, but I
didn’t use an O2 sensor.–
66 ‘UberLynx’ D, 70 FHC, 79 S2 XJ12L, 97 XJ6L
Gaithersburg, Maryland, United States
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In reply to a message from Mike Balch sent Thu 5 May 2016:

Hope you’ll forgive me for butting in as I usually post on the
E Type list however I had Walt coat mine and they lasted just
about as long as anyone else’s did. Walt also rebuilt my
engine, needless to say I would be violating forum rules if I
said any more.
Cheers,
LLynn–
The original message included these comments:

Years ago Walt Osborn told me that he had found someone who
could make the porcelain stay on the manifolds. However,
that individual died and took the process to the grave.
After that happened, Walt discontinued offering a porcelain
service for the exhaust manifolds.


Lynn G.
68/85 ots, 73 2+2, Boise, Id., United States
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In reply to a message from Rob Reilly sent Thu 5 May 2016:

I put Jet Hot ceramic coating on mine - Flat Black (not
shiny)but not cracking either after several years of track
autocrossing and slalom runs. I took no special precautions
other than driving as hard as I can. However my goal was
reducing heat in engine compartment not appearance. I have
also used Swain Tech coating on other cars with good
success, however it is white and turns a tan/brown with age.

Nick Wilson–
The original message included these comments:

My manifolds came back after porcelain coating by Prairie
Auto Porcelain in Faribault Minnesota.
http://www.jag-lovers.org/v.htm?1462386643
Tom Sparrow at Prairie had these recommendations:
Start out with short runs for a couple minutes at idle.
Then maybe 3-7 minutes then 8-13 minutes.
Always run at idle for at least 7-8 minutes to get porcelain
into the 640 plus degree range prior to driving.
Then your main expansion takes place during idling and when
take off occurs not a lot of heat rise is left.


Ponyman
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