TM  10-3930-638-24&P 4-3.   FUEL   SYSTEM   MAINTENANCE   (cont) a. Fuel Injector (cont). STEP LOCATION ITEM ACTION REMARKS CLEANING AND INSPECTION (cont) 22 Adjusting  screw Inspect Replace  if  worn,  or  if  threads  damaged (4, 9) 23 Spring  (5) Inspect Check that free length of spring is 0.563 inch and compressed length is 0.456 to 0.478 inch at 29 pounds RECONDITIONING/OVERHAUL 24 CAUTION Excessive lapping will destroy interference angle between seat and valve causing loss of chatter with poor atomization resulting in replacement of fuel injector. Injector  body Lap  valve  and Use lapping compound FSCM 05083 P/N (11) tip seat tip  seat 66-0145. Place small amount of lapping compound on valve seat and insert valve in injector body. Grip top of valve with valve retractor P/N 66-0148 and rotate valve by hand, first clockwise then coun- terclockwise for a total of 3 to 5 revolu- tions. Flush injector body thoroughly; wash valve and reassemble injector and re- test. If valve and seat are worn, seat may be tight, but chatter may have been lost in the lapping process. In such an instance replace  fuel  injector 25 Injector  body Lap  valve Use lapping compound FSCM 05083 P/N (11)  valve  guide guide 66-0145. Place small amount on guide area of valve. Bottom valve in body and grasp with valve retractor P/N 66-0148. Rotate valve 10 revolutions while raising and low- ering it very slightly. Flush and wash com- pound  from  both  parts,  assemble  fuel  in- jector and recheck fuel leak-off. If leak-off is still low, lap guide until correct leak-off is obtained. Flush fuel injector thoroughly after lapping 4-84