From 1962 to 1970, I worked for a Caterpillar
Dealer, as a field service mechanic, and a highway contractor, as a master mechanic.
It was common to be called to troubleshoot a machine when the complaint was that a
front-end loader or bulldozer was slow to raise. These devices are raised by
hydraulic cylinders that are a part of the machines hydraulic system. The problem
could be a worn pump, broken springs that hold the vanes against the cam-ring in a vane
pump, oil leaking internally past the cylinder packing, a stuck or leaking valve, a spring
broken that held a valve closed, and many others.
One of the first things
I would do, was to remove the hydraulic filter cartridge. I could immediately see
if the cartridge was collapsed or damaged. I could get a general idea as to how the
machine was being serviced. I would then cut the element open with a hacksaw.
I would lay the pleats of the element out on a table and look at the debris. As a
rule of thumb, if the hydraulic pump was badly worn, the filter would have a lot of
visible trash. A magnet would be used to help identify the metallurgy of the trash.
This would assist in determining its source within the system. A magnifying
glass would be used to assist in identifying the trash and determine its source.
Sometimes I would find pieces of a broken spring or other parts of the system that could
be identified. Sometimes I would find pieces of cylinder packing, which would point
to the cylinders being the problem. In over 80% of the time, the filter would provide
clues that led to the problem.
On one occasion, I was
called to listen to a knocking noise in the engine in a Caterpillar D8-H bulldozer.
The machine was still under factory warranty. The noise would come and go.
Another Caterpillar mechanic had listened to the noise and did not know what to do.
When I arrived at the machine, there was a discussion between the customer, the dealer and
the Caterpillar factory about the source of the noise. The opinions went from a wrist
pin knock, to a piston slap, to a rod bearing out, to its nothing, don’t worry about
it. When I listened to the engine, the knock was hard to distinguish above the
normal diesel engine noises. I could, however, hear a knocking noise and it did come
and go. With only the noise to go on, a decision to disassemble the engine could not
be made. I then cut open the filter and found sufficient debris to justify
disassembling the engine. Then the engine was disassembled, it was found that the
one of the piston wrist pin bushings was loose in its bore, and showed signs that it had
been moving in and out of the bore as the engine ran. This explained why the
knocking noise would come and go. After inspection of the engine, and except for
gaskets, the connecting rod, wrist pin and wrist pin bushing were the only parts replaced.
I have continued to
regularly cut open filters, even when a problem is not indicated.
For years, I cut open
filters with a hacksaw. Recently I found that Caterpillar makes a very nice tool for
this. The tool is well made, is similar to a pipe cutter and sells for $85.00.
In my opinion, well worth the money. It will cut open filters from 3-in. to
6-1/2-in. diameter.
I recently cut open a
spin-on diesel engine oil filter. This filter was purchased at the largest auto
parts dealer network in the U.S. It was made by one of the leading filter
manufactures in the U.S. The filter consisted of a steel head-piece with threads, so
the filter can be screwed on the engine. A steel can that was crimped to the head.
A separate cartridge inside the can and a spring at the bottom of the can which
holds the cartridge against the head. The cartridge has two metal ends that are
affixed to a metal center spool. The cartridge was not bonded to the head and only
held against the head by the spring. This permitted the steel end of the cartridge
to move against the steel headpiece during operation. Movement did take place and
metal was worn away. The wear metal was on the clean side of the element and entered
directly into the engine. With some filters we must add the filter as a source of
wear metal. I will not use this brand of filter in the future.
The next time you
replace a filter, cut open the used one. Look for debris. Try to identify the
debris. Also look closely at the construction of the filter. You may be
surprised at what you have protecting your expensive machinery.
You Can Learn a Lot from
a Filter.
By Don Searles
Machinery Maintenance for Extended Life
March 10, 2002
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