ARMY TM 9-2815-259-24 AIR FORCE TO 38G1-125-2 MARINE CORPS 09249A/09246A-24 5-113 NOTE Valve guides only need to be knurled, threaded, and reamed if valve guide- to-stem oil clearance in Step 4(i) (above) is out of specifications. (j) Knurl, thread, and ream valve guides as follows: 1 Knurl valve guides using valve guide knurler kit.  Use kit exactly as directed by kit manufacturer. 2 Thread valve guides for entire length of bore using 5/16-24NF modified internal thread tap with a major outer diameter of 0.3170 - 0.3199 in. (8.052 - 8.128 mm). 3 Hand ream valve guide to finished size to provide valve guide-to-stem oil clearance of 0.002 - 0.004 in. (0.05 - 0.10 mm).  Valves are available with 0.015 in. (0.38 mm) and 0.030 in. (0.76 mm) oversize stems. (k) Clean and inspect valve seats as follows: 1 Clean valve seats using electric hand drill with end brush.  Remove all carbon from valve seats. 2 Check valve seats for cracks, pits, or excessive wear.  Replace valve seats as required, refer to Step 7 (m). 3 Check entire combustion face for rust, scoring, pitting, or cracks. NOTE Always keep valve guides and work area clean when grinding valve seats. (l) Grind valve seats using the following steps: 1 Select a 0.3125 in. (7.9 mm) pilot that will extend approximately 2.754 in. (6.9 mm) above valve seat.  Wipe pilot stem with oily cloth and insert into valve stem guide. 2 Select an appropriate 30° angle grinding stone which is in good condition and install grinding stone on arbor. 3 Carefully lower grinding stone and arbor on to pilot until grinding stone almost contacts valve seat.