THRUSH AIRCRAFT, INC – MODEL S2R-R1340
AIRCRAFT MAINTENANCE MANUAL
4-4
Effective: 01/01/2008
A. Remove one spark plug from each
cylinder, and rotate the propeller
shaft until No. 1 piston is at the
beginning of the compression stroke.
B. Install PWA-4142 (or equivalent)
indicator in the front spark plug hole
of No. 1 cylinder (use pivot arm "A"
with hook end down).
C. Attach the red wires of PWA-2417
(or equivalent) indicator to the
breaker points of the magneto and
ground the black wire to the engine.
D. Align the cap of the indicator so the
slide slot lines up with the vertical
axis of the cylinder and the scale is
at the right of the slot. Push the slide
pointer up close to the pivot arm.
E. Turn the propeller shaft in the normal
direction of rotation until the pivot
arm pushes the slide pointer to its
farthest point.
F.
Turn the propeller shaft
approximately 90 degrees opposite
normal rotation to return the pivot
arm to the top of the slot. Adjust the
scale so that the zero degree mark
on the scale aligns with the
reference mark on the slide pointer.
G. Move the slide pointer up to align
with the 25 degree mark on the
scale. Turn the propeller shaft until
the picot arm just contacts the slide,
at which time the lower light in the
PWA-4142 indicator flashes on. The
piston is now 25 degrees before top
center.
H. At this point the lights of the PWA-
2147 indicator should flash on
simultaneously, indicating that the
points are just opening. Check the
alignment of the timing marks with a
straightedge. This will give the
correct "E" gap. Permissible limits
are 1/32-inch on either side of the
timing marks. If the timing is correct,
no further action is necessary;
however, if the timing of either
magneto is incorrect, proceed with
the remaining checks.
I. Remove the bolts that attach the
incorrectly timed magneto to its
mounting pad and move the
magneto away sufficiently to turn the
rubber drive coupling.
J. To advance the timing, turn the
rubber coupling one or two notches
in a counter-clockwise direction.
Recheck timing.
K. To retard the timing, turn the rubber
coupling in a clockwise direction.
Recheck timing.
*NOTE*
The rubber coupling has 19
notches on one side, and 20
notches on the opposite side,
allowing for a very fine
adjustment by rotating one
notch at a time.
L. After the timing has been corrected,
slide the magneto back into position,
install and lockwire the magneto
retaining bolts.
If the magneto is not properly timed,
adjust the breaker points as indicated by
the following steps:
A. With the indicator still connected and
the straightedge aligned, loosen the
contact bracket screws and turn the
eccentric adjusting screw until the
indicator light just flashes on,
indicating that the points are just
opening. Tighten the contact bracket
screws.
B. Remove one spark plug from each
cylinder. Turn propeller shaft until
No. 1 piston is at the beginning of
the compression stroke. Install
PWA-4142 (or equivalent) indicator
in the front spark plug hole of No. 1
cylinder (use pivot arm "A" with hook
end down).
C. Align the cap of the indicator so that
the slide slot lines up with the vertical
axis of the cylinder and the pivot arm
is at the top of the slot. Push the
slide pointer up close to pivot arm.
