d. Inspect the carbon brush in the distributor gear (4200 series magnetos) for wear, cracks and chipping every
500 hours. The following steps may be performed:
1. Measure carbon brush length from distributor gear shaft to end of brush. Minimum length is 11/32 inch.
If the above conditions are evident the distributor gear must be replaced.
2. Check bearing in distributor block and bearing bar for lubrication. If required, put a drop of SAE #20
non-detergent oil in each oilite.
e. Inspect the high tension lead from the coil (4200 series magnetos) to make sure it makes contact with the
carbon brush on distributor gear shaft.
f. Visually inspect the impulse coupling shell and hub (4200 series magnetos) for cracks, loose rivets or
rounded pawls every 500 hours. If pawls are rounded they may slip when latching up on the pin. If any of these
conditions are evident, the coupling should be replaced.
g. Look for frayed insulation or broken wire strands in the leads at the back of the magnetos. Ascertain that
terminals are secure and properly positioned.
h. Check the lead conduits. A few broken strands are acceptable, but if the insulation is deteriorated, replace
it. The special high temperature coating, used on the harness is provided chiefly for vibration resistance and
mechanical protection. The integrity of the harness is not sacrificed if small areas of the braid show peeling or
flaking of this coating.
i. Check the springs for breaks, corrosion, or deformation. If possible, check continuity from block with
tester or light.
j. Check insulators for cracks, breaks or evidence of "old age". Be sure they are clean.
k. Check ventilator plugs. Ventilator has drilled holes and should be in the lowest hole in the magneto to
serve as a drain for excess water or oil.
8-24. INSTALLATION AND TIMING PROCEDURE. (Timing Magneto to Engine.) (4000 series magnetos)
The magnetos can be installed and timed to the engine by the following procedure:
a Remove the top spark plug from the number one cylinder. Place the thumb of one hand over the spark plug
hole and rotate the crankshaft in the 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 the number 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 number one
cylinder. Rotate the crankshaft in its normal direction of rotation until the 25 degree mark on the starter ring gear
and hole in the starter housing align.
—NOTE—
Be sure to "Spark Out" the magnetos before installing them on the
engine. Use the following method:
1. Remove the bottom vent plug from the magneto.
2. Hold the lead wire spring 0.062 to 0.125 of an inch away from the magneto frame.
3. Turn the impulse coupling or gear one "click" at a time until a strong spark jumps between the spring and
magneto frame.
—NOTE—
Hold the magneto firmly so the coupling will not move beyond the point
where it trips and spark occurs.
PIPER AIRCRAFT
PA-28-161 CADET
AIRPLANE MAINTENANCE MANUAL
Issued: FEBRUARY. 28, 1989
POWER PLANT
1J18