Torquing It Over Page 2

Maintenance Q & A - April 2002 - Torquing It Over - Part 2
Maintenance Q & A — April 2002
By Capt. Ken Kreisler

Torquing It Over
Problems with a leaky oil pan, impeller pitting, an explanation of Total Base Number, and more.
 More of this Feature
• Part 1: Leaky Oil Pans, impeller pitting, and more
• Part 2: Total Base Number, and more

 Related Resources
• Maintenance Q&A Index

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: No phone calls, please.

Next page > Impeller Pitting, and more > Page 1, 2

This article originally appeared in the January 2003 issue of Power & Motoryacht magazine.

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