TWEAKING THE MARK XII:

PART ONE



by Walt Odets

JFK approach plateIn the 1970′s, I was a pilot flying printing plates,
bags of canceled checks, and the occasional dead body, also in a bag.
People wanted their magazines and definitely wanted their money. And
some died away from home, and their families or loved ones wanted
their bodies back. Thus, I flew three nights a week and moved all these
things around to try and make everyone happy. It was a lot of work,
I got paid $12.00 an hour, and, of course, we were constantly timing
things. Having only the most cursory interest in wrist watches at the
time, I used an Omega SeaMaster my aunt had given me on college graduation
and left it at that. At $12.00 an hour, it was a very fancy watch indeed.
And we had a pretty good Davtron timer in the panel anyway.

We did pay a lot of attention to our planes though,
and, like most pilots, we were always tweaking things to make them “better.”
We’d look for two knots of airspeed by faring over a cargo door hinge
and three knots with a new and sleeker glide slope antenna. We once
thought we got four knots by sealing the gap between the upper wing
surfaces and flaps with, of course, “flap-gap seals.” And we once even
swapped an engine for another with 80 more horsepower and a three-bladed
prop. The engine and prop gave us an honest-to-God 18 knots, but it
also sucked an extra 24 pounds (about 3 gallons) of gasoline an hour
from the 110 gallon tanks.

THE WATCH

Mark XIII
gave up flying a long time ago and took up wristwatch collecting instead.
Today, the closest thing I’ve got to an airplane is an IWC Mark XII,
every non-pilot’s favorite pilot’s watch. So, no longer having an airplane
to tweak, but still possessed–apparently–of the tweaking impulse,
I decided to tweak the Mark XII.

CaseFrom
the factory, the Mark XII is a wonderful watch. It’s sensible, it’s
handsome, it’s authentic, and it’s got integrity written all over it.
All the details, in their simplicity, are beautifully done. The robust
case is an immaculate piece of machining. The dial is legible, right
down to its glowing, applied quarter hour markers. It’s a watch that
is so simple, and so meticulously done, that it manages to transcend
its own idiom and actually come off as an Dial detail with approach plateelegant piece. This kind of integrity makes it’s hard to imagine wanting to
change a single detail. At least on the outside.

TWEAKING THE MOVEMENT

In truth, like the planes I tweaked, the Mark XII
needs tweaking neither on the outside nor inside. But
when did that stop anyone with the inclination? From the factory, the
caliber 884 is a wonderful movement. Based on the Jaeger LeCoultre 889/2,
the movement is one of the finest automatics manufactured today: 36
jewels (all the way back to the barrel Caliber 884and
click), a legendary bi-directional automatic wind system, and a pervasive
quality in every worked-through detail that is matched by only a handful
of contemporary automatics.

The caliber 884 in the Mark XII looks a lot like the
outside of the watch: a no-nonsense approach that ultimately feels elegant.
Nickel (?) plated, the mainplate and bridges are finished in a perfectly
even matte finish that gives the movement a look of simplicity and craftsmanship.
All edges are anglaged and all working parts perfectly polished. The
wheels are perfectly formed and finished. The escapement is of the finest
quality, and the watch is adjusted in five positions. Except for the
lack of decorative finish, this movement is as good as mechanical watches
get. It seems like the perfect, no-nonsense compliment to the Mark XII
that meets the eye.

EVEN SO

Caliber 887I
couldn’t help myself. The Mark XII seems such a wonderful watch
that it occurred to me that I might make it even a little better. A
gilt finish. Blued steel screws. Perlage on the plate. Geneva circles
on the bridges and cock. A platinum-rimmed rotor. And a special, time-consuming
tweak of the escapement. In fact, except for the escapement tweak, it
was another engine swap: an IWC caliber 887 for the Mark XII’s 884.
All it took was a spare Ingenieur lying Cal. 887, train wheel bridgearound,
an even more rugged, metal band watch that I wear for only the most
brutal domestic activities. As I thought about it, there was no doubt
in my mind: the 887 belonged in the Mark XII. The Mark XII deserved
the very best. And the Ingenieur would do quite well with the simplicity
of the 884 for cleaning the attic and rain gutters and doing the occasional
odd repair around the house. No hardship in that.

THE SWAP

Caliber 887, rotorInterestingly,
the 887 is shown by IWC as the base movement from which the 884 was
developed; a development, no doubt, to hold down the cost of the Mark
XII, which is almost a few thousand cheaper than an equivalent Ingenieur.
An examination of the two movements reveals that they share all but
nine parts. The main plate, barrel bridge, train wheel bridge, pallet
bridge, and balance cock are different because of the 887′s gilding,
perlage, and Geneva decoration. The rotor is different because of its
gilding and finish, and by virtue of its platinum peripheral weight
(in place of the 884′s base metal piece). Hour wheelAnd
three functional pieces–the center seconds pinion, cannon pinion,
and hour wheel–also proved to be different. Seconds pinionThese
parts, respectively, carry the seconds, minute, and hour hands. The
hour wheel, covering the cannon pinion, is show at left. The
tip of the center seconds pinion is just visible in the center. The
dial of the Mark XII, as it turns out, is slightly thicker, and stands
slightly further from the top plate. So these three pieces Caliber 884, under dialare
slightly longer, about 0.3 millimeter. The seconds pinion is shown above
right
for comparative length, the original 884 (Mark XII) part on
the left. Because the the 884 and 887 are indirect center seconds,
the pinion gear (blue arrow) is driven off the third wheel, and
the long shaft extends though the cannon pinion on the dial side of
the movement. The seconds hand is attached to the tip of the pinion
(yellow arrow). The upper pivot (as seen from the top plate,
green arrow) rides in a jewel in the barrel bridge and is stabilized
with a spring.

Calendar mechanismThe
swap was simple. These three parts were simply exchanged, the longer
parts moved to the 887 in the Mark XII.

(The under-the-dial calendar mechanism of the 887,
with bridge removed, is shown at left. The 884 under-dial view is shown
just above with the calendar bridge in place.)

CONCLUSIONS TO PART ONE

IWC buckle and plateThe
Mark XII probably didn’t need gussying up. But as Mae West once said,
“Only too much is enough,” and she often proved the point. Perhaps the
platinum rotor segment will assist automatic winding a bit, but so far
tweaking the Mark XII has been mostly about aesthetics.

Having made the swap, I proceeded to tweak the escapement
to improve the positional accuracy of the 887 in the Mark XII. I will
describe the theory and practice of these adjustments (to regulator
and balance spring) in Tweaking the Mark XII,
Part Two
,
in next month’s Horologium.

 
© 2012 Bourne In Time Inc.