Piper Comanche PA-24 Service Manual page 438

7-44. Installation and Timing Procedure. (Timing Magneto to Engine.)
The magnetos can be installed and timed to the engine by the following procedure:
NOTE: Ascertain that the breakers are correct for proper internal timing of magnetos.
NOTE: Verify correct engine timing for the airplane being worked on by checking the engine dataplate.
a. Lift the engine cowling side panels.
b. Remove the top spark plug from No. one cylinder. Place the thumb of one hand over the spark plug
hole and rotate the crankshaft in direction of normal rotation until the compression stroke is
reached. The compression stroke is indicated by a positive pressure inside the cylinder tending to
lift the thumb off the spark plug hole. In this position both valves of No. one cylinder are closed.
Turn the crankshaft opposite to its normal direction of rotation until it is approximately 35 degrees
BTC on the compression stroke of No. one cylinder. Rotate the crankshaft in its normal direction of
rotation until the 25 degrees mark on the back of the starter gear and the crankcase parting surface
are aligned, or the marks on the front of the starter ring gear and the drilled hole in the starter
housing align. (Refer to Figure 7-15 )
NOTE: The impulse coupling magneto (-21) or the -200 shower of sparks magneto can be used
only on the left side of the engine (as viewed from the rear).
VII - POWER PLANT
(PA-24-180)
PIPER COMANCHE SERVICE MANUAL
Figure 7-15. Engine Timing Marks.
2B12
04/01/09