Maintenance Practices
1. General
The maintenance practices given in this Section are limited to the compression testing of the cylinders. For more data on the engine you must refer to the Lycoming Maintenance Manual and the Lycoming Overhaul Manual.
2. Cylinder Compression Test
Do this test with the engine warm, but not hot.
A. Equipment
Item  Quantity  Part Number 
Differential compression test kit.  1  Commercial. 
Dry air pressure supply. Minimum pressure 5.5 bar (80 psi). 

B. Compression Test
Detail Steps/Work Items  Key Items/References 
WARNING: DO NOT STAND WITHIN THE DANGER AREA OF THE PROPELLER. IF THE ENGINE STARTS, THE PROPELLER CAN CAUSE DEATH OR INJURY TO PERSONS. WARNING: YOU MUST MAKE SURE THAT THE ENGINE IS SAFE BEFORE YOU TURN THE PROPELLER. MAKE SURE THAT THE IGNITION SWITCH IS SET TO “OFF” AND THAT THE SPARK-PLUG-CABLES ARE DISCONNECTED FROM THE SPARK PLUGS. SET THE THROTTLE TO “IDLE” AND THE MIXTURE CONTROL TO “LEAN CUT-OFF”. 
(1)  Set the fuel selector/shut-off valve to CLOSED. 
(2)  Make sure that the engine is safe: S The ignition switch is set to OFF. S The throttle is set to IDLE. S The mixture control is set to LEAN CUT-OFF. 

Doc # 6.02.01 Page 201
Rev. 4 09 Jan 2003

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AMM

DA 40 Series

Detail Steps/Work Items  Key Items/References 
(3)  Remove the engine cowlings.  Refer to Section 71-10. 
(4)  Disconnect the battery.  Refer to Section 24-31. 
(5)  Disconnect the spark plug cables from the spark plugs. 
(6)  Remove one spark plug from each cylinder. 
(7)  Turn the propeller four complete turns by hand in the usual direction the propeller turns. 
(8)  Connect the hose of the differential-pressure-tester (DPT) to the number 1 cylinder spark plug hole. 
(9)  Turn the propeller by hand to set number 1 cylinder piston to top-dead-center (TDC) on the compression stroke.  Feel the open end of the DPT hose. The pressure in the hose will increase to a maximum when the piston is at TDC. 
(10)  Turn the DPT reducing valve fully counter-clockwise (closed). 
(11)  Connect the air supply to the DPT.  Make sure that both gauges read zero. 
WARNING: YOU MUST HOLD THE PROPELLER FIRMLY. WHEN YOU SUPPLY AIR TO THE CYLINDER THE PROPELLER WILL WANT TO TURN. IF THE PROPELLER TURNS IT CAN CAUSE INJURY TO PERSONS. 
(12)  Hold the propeller firmly.  Use a second person. 
(13)  Connect the DPT to the tester hose (which is connected to the cylinder to be tested). 
(14)  Turn the knob of the DPT reducing valve slowly clock-wise until the input gauge reads 5.5 bar (80 psi).  The person holding the propeller must be ready to resist the propeller turning. If the force necessary to resist the turning of the propeller is high then the cylinder may not be at TDC. Gently rock the propeller backwards and forwards until the turning force is at a minimum. Monitor the gauge readings. 
(15)  Read the DPT outlet gauge and make a note of the value. 
(16)  Turn the knob of the DPT reducing valve fully counter-clockwise (closed).  Make sure that both gauges read zero. 

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Engine
AMM

DA 40 Series

Detail Steps/Work Items  Key Items/References 
(17)  Disconnect the DPT from the tester hose and remove the tester hose from the cylinder. 
(18)  Repeat items 8 to 17 for the other cylinders. 
(19)  Install the spark plugs.  Torque 47 Nm (35 ft.lb). 
(20)  Connect the spark plug cables to the spark plugs. 
　
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