TM9-2815-202-34 (d) After grinding is completed, clean valve seat insert thoroughly. Measure concentricity of insert in relation to valve guide. If runout exceeds 0.002 inch, check for bent or worn valve  guide  before  regrinding  insert. (e) Determine position of contact area between valve and valve seat insert as follows: 1.  Apply  a  light  coat  of  Prussian  blue  or  equivalent  to  valve  seat  insert. 2.  Lower  stem  of  valve  in  valve  guide  and  bounce  valve  on  seat.  Do  not  rotate  valve. 3. Remove valve and observe area of contact on valve face. Most desirable area of contact is at center of valve face. (7) Exhaust valves and springs (a) (b) (c) Insure valve stems are free from scratches or scuff marks. Valve faces must be free of ridges, cracks,  or  pitting. Replace valves if warped, excessively  worn,  or  pitted. Using  spring  tester  (87),  replace valve spring (28) when a load of less than 25 Ibs will compress it to 1.80 inches. CAUTION Replace  both  springs  under  an exhaust  valve  bridge  together. Mating a new spring with a used spring can cause unbalanced valve operation. (8) Cam followers and cam follower springs. (a)    Examine  cam  follower  springs (24) for wear or damage. Using spring tester (87),  check spring load. Replace spring when a load of less than 172 Ibs will compress it to a length of 2.125 inches. 4-197