|
Why would a bearing
farthest from the oil pump on a diesel show the most damage? J
.S., via e-mail
Bearing
failure usually occurs because of a lack of proper lubrication, due to
either contaminated oil or oil starvation, perhaps stemming from a clogged
filter, faulty oil pump, restricted oil line, or oil leak.
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
Most
new V-belts stretch after the first few hours of operation, so you will
need to check their tension frequently at first. To do this, run your
engine in neutral at 1200 rpm for about 15 minutes, after which you can
shut it down. Check the belt tension, and adjust it as necessary. The
rule of thumb for doing this is between one-half and three-quarters of
an inch of give on the longest stretch when you firmly depress the area
with your thumb. Too much tension will impose excessive loads on bearings,
and too little tension will cause slippage and excessive belt wear. Give
them one more look after eight hours of operation, and check them next
when your engine reaches 150 hours.
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.
Next page >
Making better connections, and more > Page
1, 2, 3
|