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I’ve
heard the term Total Base Number (TBN) bantered about when discussing
diesel lube oil. What does this term refer to, and why is it important?
B.K., via e-mail
Generally,
the higher the Total Base Number (TBN) of a lube oil, the higher its alkalinity
or acid-neutralizing capacity. In order to further understand what this
means, a brief discussion of the sulfur content of diesel fuel oil is
necessary.
All diesel fuel oil
contains sulfur; how much depends on the amount of sulfur in the crude
oil from which it was drawn and how extensively the crude was refined.
Sulfur content in diesel fuel oil more than 0.5 percent can cause severe
engine problems.
When sulfur is burned
in your engine’s combustion chamber, oxides of sulfur form and react
with water vapor to form sulfuric acid that can chemically attack metal
surfaces, such as valve guides, cylinder liners, and bearings. Over time
this can lead to extensive damage, eventually requiring an overhaul.
Besides reducing friction,
lube oil is designed to neutralize sulfur byproducts and thus retard engine
damage. Oil additives, primarily detergents, contain alkaline compounds
formulated to neutralize acids. Such "reserve alkalinity" is
measured by its TBN.
If you’re in doubt
as to the sulfur content of the fuel you’re using, start by querying
your fuel dock manager. If you’re still not sure, the best way to
monitor the buildup of sulfuric acid in lube oil is by having the oil
periodically analyzed. Check your yellow pages under "spectrographic
analysis" or consult your local engine distributor.
I
just completed several small but noticeable fiberglass repairs to the
cabin of my 40-foot sportfish boat. After painting the area with the same
two-part polyurethane paint used before, it was obvious the color did
not match. What can I do about this? C.G., via e-mail
There’s
no good news on this one. While it is possible to get a near color match
on small areas in inconspicuous places, in your case, you’re going
to have to repaint the entire area to get the paint to match.
Polyurethane paints
are affected by moisture, so if you’re in a region prone to morning
dew, don’t paint early in the day. Also, don’t paint in direct
sunlight. Remove all gloss by wet sanding first with 180-grit paper, then
220, then 320, wiping thoroughly between sandings. When the area is ready
to paint, follow the paint manufacturer’s instructions for mixing
and application. I’ve found that applying two or three thin coats
rather than one thick one will produce a better finish.
Avoid loading up your
brush with too much paint. If this does happen–you’ll notice
the brush dragging and paint accumulating in the ferrule–change your
brushes, making sure to thoroughly clean and dry the one you were using
in case you have to switch again.
What
is the main difference between precombustion-chamber and direct-injection
diesel fuel systems? H.T., via e-mail
A
precombustion-chamber fuel system has two combustion chambers. Combustion
begins in the first, smaller chamber and migrates into the main chamber,
where the process is completed. This type of fuel system is usually found
on older diesel engines.
Most newer engines have
direct-injection fuel systems, which are typically usually more fuel-efficient.
Fuel is injected directly into the combustion chamber through several
small holes in the fuel nozzle that create a highly atomized charge, ensuring
good combustion and a thorough burn.
While direct-injection
fuel systems are generally more efficient than precombustion systems,
they also are typically less tolerant of poor quality fuel.
Need help with a
maintenance problem? Write to Maintenance Q & A, Power & Motoryacht,
260 Madison Ave., 8th Fl., New York, NY 10016. Fax: (917) 256-2282.
e-mail: Ken_Kreisler@primediamags.com. No phone calls, please.
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