Figure 3-7.—Errors to avoid when taking liner measurements. Figure 3-8.—Trace of caliper end when determining the true diameter of a liner. practice for two persons to take the liner measurement; then any discrepancy between the two sets of readings can be rechecked. Causes Excessive or abnormal wear of cylinder liners may be  caused  by  insufficient  lubrication,  dirt,  improper starting procedures, or low cooling water temperature. The   lubricating   system   must   be   carefully maintained  in  proper  working  order.  The  method  of cylinder liner lubrication varies with different engines. The   proper   grade   of   oil,   according   to   engine specifications, should be used The engine must not be operated in a dirty condition. The air box, crankcase, and manifold should be cleaned and maintained in a clean condition, to avoid cylinder wear and scoring. (Attention to the air cleaner, oil filters, and oil centrifuge are the best precautions against the entrance of dirt into the engine.) Improper starting procedures will cause excessive wear on the liners and pistons. When an engine is first started,   some   time   may   elapse   before   the   flow   of lubricating oil is completed; also, the parts are cold and condensation  of  corrosive  vapors  is  accelerated accordingly. These two factors (lack of lubrication and condensation  of  corrosive  vapors)  make  the  period immediately  after  starting  a  critical  time  for  cylinder liners. If an independently driven oil pump is installed, it must be used to prime the lube oil system and build up oil pressure before the engine is started The engine should not be subjected to high load during the warm-up period.  Follow  the  manufacturer’s  instruction  manual concerning warm-up time and load application for the engine  concerned The cooling water of an engine should always be maintained within the specified temperature ranges. If the temperature is allowed to drop too low, corrosive vapors will condense on the liner walls. Repairs Cylinder   liners   worn   beyond   the   maximum allowable limit should be replaced. You will find the maximum  allowable  wear  limits  for  engines  in  the appropriate  manufacturer’s  technical  manual  or  the Diesel  Engine  Wear  Limit  Chart  available  from  the Naval Sea Systems Command. In the absence of such specific   information,   the   following   wear   limits (established by NAVSEA) apply in general to 1.  two-stroke  cycle  engines  with  aluminum pistons: 0.0025 inch per inch diameter, 2.  slow-speed  engines  over  l8-inch  bore:  0.005 inch per inch diameter, and 3. all other engines: 0.003 inch per inch diameter. If you must remove a liner, follow the instructions given on the appropriate maintenance requirement card (MRC) or in the manufacturer’s technical manual for the particular  type  of  engine.  Figure  3-9  illustrates  the method  generally  used  to  remove  a  cylinder  liner. To  remove  the  cylinder  liner,  proceed  as  follows: 1. Drain the water from the engine. 2. Remove the cylinder head. 3. Remove the piston(s). 3-6