TM  9-2815-202-34 NOTE (b)  Replace  valves  if  warped,  excessively worn,  or  pitted. Maximum  amount  exhaust  valve  should  protrude  beyond  cylinder  head”  and  still maintain proper piston to valve clearance is shown. Grinding reduces thickness of valve seat insert and valve recedes into cylinder head. Replace valve seat insert if valve recedes  beyond  limits. (d)  After  grinding  is  completed,  clean  valve  seat  insert.  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. Observe area of contact on valve face. Most desirable area of contact is at center of valve  face. (7)  Exhaust  valves  and  springs (a)  insure  valve  stems  are  free  from scratches  or  scuff  marks.  Valve  faces must be free of ridges, cracks, or pitting. (8) (c)  Using  spring  tester  (89),  replace  valve spring (28) when a load of less than 25 pounds  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. Cam followers and cam follower springs. (a)  Examine  cam  follower  springs  (24)  for wear or damage. Using spring tester (89), check spring load. Replace spring when a load of Iess than 172 pounds ^- will compress it to a length of 2.125 inches. Change 1 5-49