Atomic 4 mechanical fuel pump rebuild
By Terry Kuhn  (ETK FIXR@aol.com)

1) Shut off the fuel supply to the pump, remove the inlet hose/pipe and cap or plug
it if possible.
2) Remove the outlet line to the carburetor, you may have to remove it at both ends.
3) Remove the two 1/2" hex-head bolts holding the pump to the engine.  The upper bolt
may be removed easier by removing the sediment bowl and by using a 1/4" drive ratchet
and a 6" extension with a short socket to clear the housing.  Pull the pump from the
engine and clean the block surface.
4) If not already done remove the sediment bowl.  If the bowl has not been removed
for some time the retaining bail may be rusted solid.  Do not force the screw as it
breaks very easily.  Try pulling the bail ends out of the upper housing and soaking
the bail in penetrating oil.  With the bowl off you can then remove the gaskets and
screen.  Dump the gasoline in the bowl into a suitable container.
5) Hold the pump over the container, point the fuel outlet into it and operate the
manual priming bail several times.  This will empty most of the gasoline from the
pump.
6) Start the pump disassembly by removing the fuel fittings and the 1/4" pipe plug
from the upper housing.
7) Remove the six- (6) screws on the upper housing.  If the diaphragm holds the two
halves together you can gently pry at the engine flange side on the top.  Avoid
chiseling in between the two halves as this might mar the gasket sealing services and
cause a fuel leak.
8) In the upper section, remove the screw from the check valve retaining plate.  The
inlet valve faces up and may be gently pried out from above.  The outlet valve faces
down and may be pushed up by inserting a small screwdriver into the fuel outlet port.
9) While holding the spring cover down remove the three- (3) screws securing it.  The
operating springs are sandwiched in between the cover and housing and may be removed
after the cover is off.
10) Pull one of the hairpin clips from the diaphragm-retaining shaft and push the
shaft out.
        The diaphragm may have to be pressed into the housing for the shaft to clear
the side wall.
11) Using a small screwdriver pry one of the semicircular clips from the rocker
shaft.  Note the position of the laminated rocker and diaphragm drive bars before
removing them, it is critical to get them back in correctly. Use a punch and hammer
to drive the shaft from the housing.
12) Clean all the parts thoroughly being sure to get all of the old gaskets off.  The
pumps have a tendency to build up corrosion in the upper housing due to condensation
during winter lay-ups.  Be sure to clean this out as it can get flushed into the
carburetor and cause the inlet valve to stick open.
Note: use of gasket cement such as Permatex aviation or #2 is recommended on both
sides of the diaphragm, the spring cover gasket and the engine flange gasket.
13) Start re-assembly by replacing the retaining shaft and hairpin clips on the
diaphragm operating bars.  Align the laminated rocker in between the bars and slide
them back into the housing.  Reference the parts diagram if needed.  Carefully push
the rocker shaft back into the housing and through the bars and cam.  Press the
semicircular clips onto each end of the shaft.
14) Put the manual priming bail into its slots, insert the diaphragm and pin it with
the retainer and hairpin clips. Turn the housing upside down, standing on the
diaphragm, and put the cover gasket and springs with their metal cups in.  One spring
sits on the diaphragm shaft the other on the rocker point.  Carefully lower the cover
over the springs being sure that they drop into the pockets in the cover.  Hold the
cover down while installing the screws.
15) Put the check valves and their gaskets into the upper housing, inlet pointing up,
outlet pointing down, and install the retainer plate and screw.
16) Place the upper housing onto the diaphragm with the sediment bowl facing toward
10 o'clock when viewed from above.
17) Install the sediment screen, bowl gasket and leather gasket.  You may need to wet
the leather slightly to allow it to stretch.  Put the bowl on and secure it with the
bail.
18) Re-install the fuel fittings and the 1/4" plug, the plug faces the engine flange.
19) If possible, procure two 5/16-18 by 11/4" socket head screws.  These have an
allen head socket which makes it much easier to install the upper bolt as you can
hold the screw on the end of the allen wrench while putting it in the hole. If the
pump will not seat all the way or the engine will not turn over by hand after the
pump is on, take the pump off and check the position of the rocker and bars in
step13.  If they are upside-down it will break the rocker.
20) Reattach the fuel lines and test for leaks.

Engines by TK    165 Graystone Road, Wilmington, NC 28411   (910) 686-1086