Page 218 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

UH) Major Process Equipment Maintenance and Repair

Plasti-Gauge@ wire, which can be purchased in any auto parts store, is
a very good medium and it is generally considered to give reliable read-
ings. Its use suffers three disadvantages, however:

1. It is time consuming.
2. The bearing has to be dismantled at least twice, which betters the
chances for human error.
3. It cannot be used on vertically split bearings common to engines
where the crankshaft is removed through the side.
The dial indicator method can be used on main bearings, i.e., a dial
indicator is clamped to the main bearing cap with the button of the indica-
tor set on the shaft. The shaft can be raised by a very small hydraulic jack
until it contacts the top of the bearing and the clearance is recorded on the
dial. The feel of the shaft hitting the top of the bearing and the return to
the bottom is quite pronounced. Several cycles of this movement will re-
peat the indicator reading.
Some people prefer to use a jack on each side of the journal being
checked. If this method is used, caution is necessary in placing the jack to
assure a solid base support for the jack. Users have had good success
with this method and highly recommend it. Difficulty in raising the shaft
will be encountered when the alignment is such that the shaft is in a re-
verse bend. There is no need for controversy in using the dial indicator to
check connecting rod clearances. It has all the advantages, it is fast and
precise, and it does not require disassembly. Any readings recorded by
this method that are above or below specifications or a previous reading
are reasons for disassembly and inspection.

Maintenance of Upper Engine

A review of what has been covered will show that the lower half of the
engine has received complete attention. This was accomplished by simple
inspections that required a minimum of downtime or disassembly and
without expensive instruments. Everything from the connecting rod to
the top of the engine will be dealt with in a similar fashion.
Piston Rings-Piston ring trouble is one of the most dreaded problems
of an internal combustion engine. Engines operating with faulty rings are
vulnerable to cracked pistons, cracked heads, worn liners or piston sei-
zures with subsequent crankcase explosions. Faulty rings will also reduce
the life of lubricating oil. Consequently, it is very important to be contin-
ually alert for any indicators that will point up ring condition. In large
two-cycle engines, ring trouble caused by problems in the port area will
result in a distinct clicking noise at the base of the cylinder. Therefore,