TM 9-2815-250-24&P 3-5. CYLINDER HEADS REPAIR (continued). d. MACHINING Grind  exhaust  valve  (16)  and  valve  seat  (21)  to  a  45- degree angle.  If necessary, repeat for other valves. e.   INSTALLATION NOTE · There  are  two  valves,  intake  and exhaust,  in  each  of  two  cylinder heads.    Follow  steps  1  and  2  for each of them. · Part numbers are different for the intake   and   exhaust    valves,    but the  valves  are  installed  the  same way.      This   procedure   describes the    installation    of     an     exhaust valve. 1. Install  exhaust  valve  (16)  in  cylinder  head  (6). Place   base   spring   washer   (15)   over   exhaust valve (16).  Install valve spring (14) over exhaust valve (16) so it is seated on base spring washer (15).  Place valve spring retainer washer (13) on valve spring (14). 2. Using    a    valve    spring    lifter,    compress    valve spring  (14)  and  install  two  valve  spring  retainer locks (12) in valve spring retainer washer (13). 3. Install  two  new  O-rings  (10)  in  two  grooves  on each of two guides (1). 4. Install    two    guides    (1)     in     two     recesses     in crankcase (11). 3-18