Q & A — August 2004
By Capt. Ken Kreisler
| Bearing damage in a
diesel engine, making better electrical connections, and more.
Why would a bearing
farthest from the oil pump on a diesel show the most damage? J
.S., via e-mail
In a diesel, oil is pumped through the oil cooler and then through one or more filters. Bypass valves ensure there is a sufficient supply of lubricant if a filter or cooler becomes clogged. From the filter, oil flows through various passages to components requiring lubrication and cooling, then returns to the oil pan.
Excessive bearing wear can occur if the oil system operates in bypass mode for an extended period of time, bypassing the filter and allowing contaminants to accumulate in the oil. The accompanying diagram shows a normal, lubricated crankshaft journal and bearing. Catastrophic bearing damage results when a crankshaft journal and bearing receive an insufficient supply of oil. The result is bearing material displaced by the crankshaft journal, the amount of damage depending on the duration of the oil starvation.
A “smeared” bearing occurs when the top lead-tin overlay is relocated, usually in the center of the bearing. A “scuffed” bearing occurs when the deeper aluminum layer is exposed, also usually in the center. The most severe damage is a “seized” bearing, in which bearing material melts and becomes welded to the crankshaft surface.
In cases where the problem is oil starvation, the bearing farthest from the oil pump usually shows the most damage because it received the least amount of oil. In cases where oil is bypassed around the filters, contaminated oil usually causes excessive wear that shows up equally on all bearings.
How long after installing
a new V-belt should it be checked, and are there any other tips for maintaining
them? A.N., via e-mail
Preventive maintenance calls for regular inspection for nicks, cuts, abrasion, and glazing. If you find a belt that needs to be changed, it’s most likely a good idea to change all your belts at the same time. And keep several spares on board just in case you need one when you are away from the dock.
This article originally appeared in the July 2004 issue of Power & Motoryacht magazine.