Piper Comanche PA-24 Service Manual page 501

Magneto Type
S6LN-200
7A-73. 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. 1 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. 1 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. 1 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)
C. Rotate the drive gear on the magneto until the chamfered tooth on the distributor gear inside the
magneto aligns with the white pointer as seen through the inspection hole in the magneto housing.
D. Without allowing the gear to turn from this position, install the magneto with gasket on the engine
and secure with washers and nuts.
E. Tighten nuts sufficiently to hold magneto in position and yet allow it to be rotated.
F. Fasten the ground lead of the timing light to all unpainted metallic portions of the magneto and one
positive lead to the terminal side of the main points.
04/01/09
PIPER COMANCHE SERVICE MANUAL
Table VIIA-II. Timing Data
Part No.
10-163010-2, -4, -5, -9, -11
10-163010-3, -6
10-163010-10
2D23
Magneto
Degree Retard
30
45
37 1/2
VIIA - POWER PLANT
(PA-24-250/260)