ARMY TM 9-2815-259-24 AIR FORCE TO 38G1-125-2 MARINE CORPS 09249A/09246A-24 3-16 k. Do not allow grease or oil to enter a blind threaded hole.  Hydraulic action present when bolt or stud is tightened could split or stress housing. l. Bolts or nuts must be loosened one quarter turn and then tightened to specified value to check or re- torque. m.    Steel ISO metric bolt and nuts can be identified by the letter M either on head or on one hexagon flat.   The strength grade will also be marked on top or on one flat. n. Nuts with identification marks on face will reduce frictional area of surface.  Nuts with identification marks on one face must be installed with unmarked face towards component. o. Cover or cap all openings to prevent entry of foreign material when removing or disconnecting fuel lines, lubrication lines, or coolant hoses.  Remove covers and caps upon installation. 3.7.1. TEST ENGINE COMPRESSION PRESSURE. NOTE Before beginning test, ensure that batteries are fully charged and injection nozzle area is thoroughly cleaned. a. Run engine to bring up to normal operating temperature.  (From a cold start, operate engine 10 to 15 minutes then shut off engine). b. Shut off fuel supply and remove fuel injection nozzles, refer to paragraph 4.6.2. c. Install adapter (JT01679) with O-ring in injection nozzle bore.  Use holding clamp (JT02017) to hold adapter in position.  Install hold down screw in clamp and tighten screw to 27 lb-ft (37 Nm).  Attach test gage (JT01682) to adapter. Refer to Appendix B, Section III. d. Refer to TM 9-6115-671-14, and using DEAD CRANK switch, (or other applicable device), turn crankshaft for 10 to 15 seconds with starter (150 rpm minimum cranking speed).  Record pressure reading. e. Compare readings from all cylinders. f. Compression pressure must be 350 psi (2400 kPa) minimum.  The difference between the highest and lowest cylinder must be less than 50 psi (340 KPa). g. If pressure is much lower than shown, remove gage and apply oil to ring area of piston through injection nozzle bore.  Do not use too much oil.  Do not get oil on the valves. h. Test compression again.  If pressure is still low, it is possible that valves are worn or sticking, or o- rings are worn or stuck. 3.7.2. MEASURE ENGINE BLOW-BY. a. Place a hose with a standard gas gage in end of crankcase vent tube. b. Run engine at rated speed and load (engine at operating temperature and run-in, with at least 100 operating hours).