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Stan,
Here is the procedure from the Bendix Mag manual, pages 9-9 & 9-10:
before quoting the manual, there are tools and fixtures listed in the
manual that I will not include in this posting because you wont be able
to obtain them, but you can do it all by hand without these holding tools
and fixtures. However- you must have the timing plate and pointer- you
CANNOT do this without the timing plate, pointer and a magneto squealer
box (timing light and buzzer to tell you when the points open)
Assuming that the magneto is assembled and you know that the rotor is
pointing to the #1 cylinder contact on the cap:
9.2.9 B.
Insall the timing plate assembly to the magneto upper housing. Turn rotor
in direction of normal rotation until painted chamfered tooth on
distributor gear is approximately centered in inspection window. Then
turn it back until rotor locates in its neutral position.
NOTE:
The neutral position is located by "feel" of rotor. As rotor is
turned a few degrees backward from where distributor tooth is centered in
inspection hole, magnet will have a natural tendency to "pull in"
and locate in the neutral position.
9.2.9 C.
Hold rotor in this neutral position. Install the pointer of the timing
kit on the cam screw and align pointer with zero degree mark on timing
plate.
9.2.9 D.
Now turn rotor in normal direction or rotation until pointer indexes with
the respective 10 degree mark (e-gap). Using the magneto buzz box (or
equivalent) adjust contact points to just open at this position.
NOTE:
Main contact of a clockwise magneto is located on the left hand
side of contact compartment looking into contact compartment. Main
breaker of a counterclockwise magneto is on the right side of contact
compartment. Normal direction of magneto rotation is determined by
magneto model number. An S4LN-21 magneto is a Left hand rotation magneto
as denoted by the "L". Rotation of the magneto drive gear is to the left
when viewed from the BOTTOM of the drive gear, with the drive gear
retaining nut and cotter key facing toward you.
9.2.9 E.
Now continue turning rotor until the cam follower on the contact assembly
is on the high point of the cam lobe. Hold magneto in this positon and
measure contact point clearance. Clearance must be .018 plus or minus
.006 inch. If clearance is over .024 inch, readjust contact to .024 inch
opening. If clearance is under .012 inch, readjust contact to .012 inch
opening. If contact assembly was re-adjusted, recheck E gap as previously
described. Replace contact assembly if E gap is less than 6 degrees or
more than 14 degrees with contacts set within specification. Tighten all
screws and remove all tooling.
SO- the basic layman's gist of all of this is that when the rotating
magnet is at neutral, as felt when rotating the magnet, the contact
points should just begin to open 10 degrees past this point. Your mag
light buzz box should indicate this just as the points open. This sets
the beginning point of the opening of the breaker points- then once the
points are fully open on the high point of the cam lobe, you set the
opening at .018 and if the points arent excessively worn out this should
do it.
To install your mags on your engine remember that the right mag runs the
top plugs, the left mag runs the bottom plugs (unlike a Cessna 150 where
they are crossed over). Put your crankshaft at 28 degrees and install the
right mag with the mag's breaker points at the E gap position (just
beginning to open as indicated by the timing light buzz box.) Then rotate
the crank to 30 degrees before TDC and install the Left mag in the same
fashion. Snug them down with the nuts.
Now install your mag buzz box again and rotate the crankshaft through-
with plug wires off (and plugs out-it's easier). When your crank hits 28
degrees, the buzz box will indicate points opening. Continue rotating the
crank and then at 30 degrees the left mag should indicate points opening.
Loosen nuts and move mag to adjust as necessary. If they dont indicate on
the buzz box it's probably because of the impulse couplings. Turn the
prop past TDC and when the impulse couplings release (clunk) then turn
the prop back to where you were, and then it should work.
You have internally timed the mags so that the points open at E gap, you
have adjusted the point gap, and you have properly timed the mag to the
engine.
Jan Z
Fresno, CA
call me if you have trouble 559-224-4088
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