Genuine Spares are Best! OR
ARE THEY?
While this statement is almost
universally true, specifics can sometimes tell
another story. If the good running and reliability of
your Land-Rover engine is important to you, you may
want to read on...
Let's consider the case of
the "lowly and oft forgotten" distributor.
For purposes of discussion, consider a
new-off-the-shelf, Genuine Land-Rover or Genuine
Lucas distributor... typically not always... the mind
set among more seasoned Land-Rover owners who care
about their vehicles is that Genuine parts are the
best at the end of the day, and this mind-set keeps
them from difficulty to a much greater extent than
those who shop the cheapest price. In the case of the
distributor, however, there may just be room for
comparison.
When British Northwest began
restoring (rather than simply rebuilding)
distributors in about 1985, the task was given to
Chris, our chief machinist. Chris is a technician who
delights in fine work, and he took up the assignment
with the fervor and attention to detail for which we
had come to appreciate him over the years. A day or
so later he came to me with his first completed
rebuilds. I was impressed. Very impressed. I
reflected on the new distributors which we had
recently installed, both Genuine Lucas as well as
Genuine Land-Rover, and immediately sensed a
difference. I asked Chris to get a new distributor
from the shelf for purposes of comparison. He was
back in a jiffy with the results, which, to my mind,
were astonishing.
Let's take a brief step
backwards at this point to examine one of the basic
design characteristics of all points-type
distributors. The main shaft of the majority of
distributors of this period run in bronze bushings.
The contact points bear directly on a
four-or-six-lobe cam, such that any play at the cam
will have a direct, one-to-one relationship with the
point gap, and dwell. Thus, if the cam is worn, let's
say, ten thousandths [.010"], the error will
also show up as ten thou at the points. This is the
basic field test for any distributor; if perceptible
play is found by moving the cam from side to side,
the distributor cannot function correctly.
Back to our new versus
restored distributors. What Chris discovered is that
his freshly restored distributors showed radial play
at the cam from 1.750 thousandths to 2.250. This
works out to about about seven percent runout, which
may not seem all that good, until we compare those
numbers to the new Genuine distributors, which,
across the board, we found dial in at about 8.750 to
9.35 thou, or more than four times greater than the
restored units. These figures are achieved by
measuring the radial play of the cam when using a
dial indicator.
The precise firing
characteristics of the ignition system on any
internal combustion engine is directly dependent on
the accuracy of the distributor [or magneto]. Precise
timing yields precise firing of the spark plugs,
which places the detonation point of the fuel charge
at the optimal moment for the firing cycle of each
and every cylinder, throughout the r.p.m. range,
assuring the most even firing, the smoothest running
and consequently the greatest possible horsepower. In
the absence of an accurately calibrated and properly
set up distributor, correct combustion simply cannot
possibly take place. Regardless of whether a
distributor is new, rebuilt, used or otherwise,
unless the mainshaft bushing and shaft are accurately
and closely matched, and play is minimised to the
greatest degree possible, then correct and optimal
ignition is simply impossible. In addition to this
the fit of the cam on the shaft must also be within
the closest tolerances possible, and smooth running
is similarly impossible. Essentially any engine out
of time to this degree of error will shake itself to
an early demise. The better the fit, the more
accurate the fire, and the smoother, longer, and
stronger the engine will run.
Getting back to our
remanufactured units, Chris fully disassembles a good
rebuild candidate, cleaning and inspecting it
carefully for defects or potential trouble spots. He
then replaces the bushing, and completely restores
any and all interior mechanicals. The contact breaker
plate is checked and any faults are rectified, or
sometimes a better plate may need to be installed.
Before a good distributor is completed it may take
the parts of several units to achieve the quality
level we require. Similarly, the counterweights,
springs, terminal bush and lead are all checked
either mechanically, electrically, or both, so that
the end product is of the very highest possible
quality. The vacuum advance is checked and replaced
if necessary, and, once all the mechanical work is
completed the distributor is then tested and compared
to the factory specs, and adjusted as necessary.
After the physical and electrical properties of the
rebuilt distributor are checked and found correct
from a static standpoint, then the distributor is run
up on the calibration fixture to make certain that
the correct operational parameters are held
throughout the entire r.p.m. range. Essentially what
is taking place is the blueprinting of the
distributor, and the results can be appreciated
immediately.
Dr. Christopher Jacobs, in his book,
"Optimising Automotive Electrical Systems",
states that ALL Bosch, Lucas and Magnetti Marelli
ignition systems should be scrapped, wholesale;
relegated to the junk heap before they see the light
of day. A little extreme? Probably, at least for the
intended application. After all, hundreds of
thousands of Land-Rovers have been successfully
plying the "impenetrable reaches" of the
remote corners of the planet for more than fifty
years, so on the face of it this is somewhat of a
radical interpretation of the status quo... HOWEVER,
I think it could be safely said that as many as 80%
of Land-Rovers on the American road today could
easily benefit from the enlightened attention of a
qualified and knowledgeable distributor technician.
For lack of familiarity with the best performance of
which Land-Rover is capable, many owners accept the
truism that their Land-Rover "runs really
well", and never get a taste of the exceptional
capability of this most admirable of four-wheel-drive
machines ever conceived. In the absence of a good
local distributor technician, relief is as near as
the friendly UPS truck or local post office.
