Page 269 - Reciprocating Compressors Operation Maintenance

254 Reciprocating Compressors: Operation and Maintenance

straight crankshaft is expected. If there is no deflection, there may be a
problem.
As mentioned earlier, the deflection gauge should be read with the
crankshaft jacked downward after 180° rotation. This allows deflection
to be seen that otherwise might be missed if the crankshaft is bent just
enough to be held "straight" by the main bearings.
Journal runout is normally checked with a dial indicator on the side of
the crankshaft at the level of the main bearing parting line to cancel out
the effects of crank weight. With the bearing removed and the dial indi-
cator against the main bearing journal at the bearing oil groove location,
rotate the crankshaft and observe the readings at 90° intervals to get the
complete picture. If the crankshaft and bedplate are both straight and
properly aligned, the readings should be within about .GOT' of instruction
manual specifications.

CRANK BEARING FAILURES

Failure of these bearings is actually more common than loss of mains.
When it occurs, always check the connecting rod bearing bore for signs
of distortion and destructive overheating.
Remove the connecting rod and check the bore for roundness with the
bearing removed. Before reinstalling the rod, temporarily install the new
bearings and torque the bolts, then check the rod bore for roundness
again. An out-of-round bore may show up during either, but not necessar-
ily in both, checks.
When installing replacement bearings, always be sure to properly
torque the caps to ensure proper bearing crush for good fit and effective
heat transfer. The crosshead pin bore of the rod should also be inspected
for roundness and the clearances checked whenever the connecting rod
bearing is replaced. It is good practice to confirm that the centerline is
parallel through both bores of the connecting rod.

BEARING ASSEMBLY CHECKLIST

This checklist itemizes the most important items that should be veri-
fied prior to and during assembly of crankshaft bearings.

• Ensure bearings are the correct design.
* Bearings should be free from burrs and thoroughly cleaned.