adjust the regulator of the regulated pressure gauge  compression tester to obtain 80 psi.  After staking the valve in this manner, rotate the engine with  the starter and re-check the compression. Do not make a  compression check after staking a valve until the crankshaft  has been rotated either with the starter or by hand to re-seat  the valve in normal manner. The higher seating velocity  obtained when staking the valve will indicate valve seating,  even though valve seats are slightly egged or eccentric.  This procedure should only be performed if approved by  the manufacturer. Cylinders having compression below the minimum specified  should be further checked to determine whether leakage is  past the exhaust valve, intake valve, or piston. Excessive  leakage can be detected (during the compression check):  Next to valve blow-by, the most frequent cause of  compression leakage is excessive leakage past the piston.  This leakage may occur because of lack of oil. To check this  possibility, apply engine oil into the cylinder and around the  piston. Then, re-check the compression. If this procedure  raises compression to or above the minimum required,  continue the cylinder in service. If the cylinder pressure  readings still do not meet the minimum requirement, replace  the cylinder. When it is necessary to replace a cylinder as a  result of low compression, record the cylinder number and  the compression value of the newly installed cylinder on the  compression check sheet. If low compression is obtained on any cylinder, turn the  engine through with the starter, or re-start, and run the engine  to takeoff power and re-check the cylinder, or cylinders,  having low compression. If the low compression is not corrected, remove the rocker- box cover and check the valve clearance to determine if the  difficulty is caused by inadequate valve clearance. If the low  compression is not caused by inadequate valve clearance,  place a fiber drift on the rocker arm immediately over the  valve stem and tap the drift several times with a 1 to 2 pound  hammer to dislodge any foreign material that may be lodged  between the valve and valve seat.  Reciprocating engine cylinders are designed to operate for  a specified time before normal wear requires their overhaul.  If the engine is operated as recommended and proficient  maintenance is performed, the cylinders normally last until  the engine has reached its TBO. It is known from experience  that materials fail, and engines are abused through incorrect  operation; this has a serious effect on cylinder life. Another  reason for premature cylinder change is poor maintenance.  Therefore, exert special care to ensure that all the correct  maintenance procedures are adhered to when working on the  engine. Some of the reasons for cylinder replacement are: 1.  Low compression 2.  High oil consumption in one or more cylinders 3.  Excessive valve guide clearance 4.  Open the shutoff valve and attach the air hose quick- connect fitting to the spark plug adapter. The shutoff  valve, when open, automatically maintains a pressure  in the cylinder of 15 to 20 psi when both the intake  and exhaust valves are closed. 5.  By hand, turn the engine over in the direction of rotation  until the piston in the cylinder being tested comes up  on the compression stroke against the 15 psi. Continue  turning the propeller slowly in the direction of rotation  until the piston reaches top dead center. Top dead center  can be detected by a decrease in force required to move  the propeller. If the engine is rotated past top dead  center, the 15 to 20 psi tends to move the propeller in the  direction of rotation. If this occurs, back the propeller up  at least one blade prior to turning the propeller again in  the direction of rotation. This backing up is necessary to  eliminate the effect of backlash in the valve-operating  mechanism and to keep the piston rings seated on the  lower ring lands. 6.  Close the shutoff valve in the compression tester and  re-check the regulated pressure to see that it is 80 psi  with air flowing into the cylinder. If the regulated  pressure is more or less than 80 psi, readjust the  regulator in the test unit to obtain 80 psi. When closing  the shutoff valve, make sure that the propeller path is  clear of all objects. There is sufficient air pressure in  the combustion chamber to rotate the propeller if the  piston is not on top dead center. 7.  With regulated pressure adjusted to 80 psi, if the  cylinder pressure reading indicated on the cylinder  pressure gauge is below the minimum specified for the  engine being tested, move the propeller in the direction  of rotation to seat the piston rings in the grooves.  Check all the cylinders and record the readings. 1.  At the exhaust valve by listening for air leakage at the  exhaust outlet; 2.  At the intake valve by escaping air at the air intake;  and  3.  Past the piston rings by escaping air at the engine  breather outlets. Cylinder Replacement 10-41