Page 304 - Reciprocating Compressors Operation Maintenance

Overhaul and Repair of Reciprocating Compressors 289

during operation they will not enter the oil scraper rings and destroy the
oil film.
When installing pistons or adjusting end clearances, it is desirable to
have more clearance at the head end than at the crank end because expan-
sion from running heat and normal connecting rod bearing wear tend to
increase the crank end clearance. For this reason, when setting the piston
end clearance, make the head end clearance approximately two thirds of
the total and the crank end clearance one third.
To adjust piston end clearance, use the following procedures.

1. Lock out the electrical switch to prevent accidental start up of the
compressor.
2. Remove all gas pressure from cylinders.
3. Remove one valve from each end of cylinder.
4. Bar compressor over until piston is at end of the stroke.
5. Using feeler gauge, measure the distance between the face of the
piston and the cylinder head. Note this measurement.
Caution: Be sure that feeler gauges are long enough so that your
hands are never in the cylinder between piston and cylinder head.
Also, never attempt this measurement with the compressor running.
6. Bar compressor over again to bring piston to the end of its stroke at
the opposite end.
7. Measure this amount, using feeler gauges.
An alternative method of checking the clearance between piston
and head is to use soft lead wire. Bar over until the lead wire is flat-
tened, and measure this thickness with a micrometer.
8. Take the difference in clearance between the two readings and
screw the piston rod in or out of the crosshead to make this clear-
ance two-thirds on the head end and one-third on the crank end.
Note: If the piston rod cannot be turned by hand, use a strap wrench
or a socket on the piston nut. Never use a pipe wrench on the rod.
9. Tighten the crosshead nut and fasten locking devices.
Caution: Place a block of wood between the frame and the
crosshead when the nut is being tightened. This will prevent the
crosshead from turning and distorting the connecting rod and bear-
ing. Add tram marks for point of reference.
10. Be sure to record the crank end and head end clearance settings for
future reference.