
Specications Information and Repair Parts Manual 3993-96, 3993-Z6, 3994-96 & 4210-96
3993-254-00 2 3/2017
MAINTENANCE
MECHANICAL SEAL REPLACEMENT
Refer to Figures 1 and 2
NOTE: Always replace the seal seat (Ref. No. 12), seal head
(Ref. No. 13) and shaft sleeve (Ref. No. 3) to ensure proper
mating of mechanical seal components!
See Figure 1
1. Unthread cap screws (Ref. No. 20) and remove casing
(Ref. No. 19) and casing seal (Ref. No. 37) from casing
cover (Ref. No. 6).
2. Unthread screws (Ref. No. 15) and remove volute (Ref. No.
14) from casing cover.
3. Unscrew impeller (Ref. No. 2) from the engine shaft.
Remove the impeller shim (Ref. No. 5), shaft sleeve and
seal head from engine shaft. Use a rubber mallet or soft
block of wood to loosen impeller. Turn it counterclockwise.
Disconnect spark plug wire and battery to prevent
accidental starting.
4. Unthread cap screws (Ref. No. 9) and remove the adapter
(Ref. No. 7) and casing cover from the engine mounting
face.
5. Push seal seat from the casing cover recess with a
screwdriver.
6. Clean the casing cover recess before inserting a new seal
seat.
7. Carefully wipe the polished surface of the new seal seat
with a clean cloth.
8. Wet the rubber portion of the seal seat with a light coating
of soapy water.
9. Press the new seal seat squarely into the cavity in the
casing cover. If the seal seat does not press squarely into
the cavity, it can be adjusted in place by pushing on it with
a piece of pipe. Always use a piece of cardboard between
the pipe and the seal seat to avoid scratching the seal
seat. (This is a lapped surface and must be handled very
carefully).
10. After the seal seat is in place, ensure that it is clean and
has not been marred.
11. Using a clean cloth, wipe the shaft and make certain that it
is perfectly clean.
12. Secure the adapter on the engine mounting face.
NOTE: Tighten cap screws EVENLY to avoid cocking rabbet on
engine mounting face.
13. Apply a light coating of soapy water to the inside rubber
portion of seal head and slide onto the shaft sleeve. Slip
the shaft sleeve with seal head onto the engine shaft.
IMPORTANT: Before installing new shaft sleeve, apply a bead
of non hardening, pliable sealant (such as Permatex® Form-A-
Gasket® No. 2) around motor shaft shoulder.
Do not touch or wipe the face of the polished part of the
seal head.
14. Replace any impeller shims removed in disassembly.
15. Screw the impeller back in place tightening until it is seated
against shims and shaft sleeve.
NOTE: Check to be sure that the shaft sleeve (Ref. No. 3) is in
place against engine shaft shoulder. Model 3993-96 requires a
shaft ange (Ref. No. 4).
16. Remount volute with fasteners.
17. Refer to section titled Shim Adjustment at this time if shaft
sleeve or any other parts listed therein have been replaced.
18. Inspect position of apper valve assembly (Ref. No. 16) to
ensure proper movement and sealing.
19. Replace o-ring seal on volute rabbet.
NOTE: Always inspect o-ring seals. Replace when cracked or
worn. Wet o-ring with soapy water for ease of assembly.
20. Remount casing.
21. Remount any other parts and reconnect spark plug wire
and battery (if so equipped). Pump should now run with
renewed original performance.
SHIM ADJUSTMENT
1. When installing a replacement impeller, engine, shaft
sleeve, adapter, or volute, it may be necessary to vary the
number of impeller shims (Ref. No. 5) that will be required.
This is easily done by adding one shim more than was
removed and reassembling the pump as described in
Mechanical Seal Replacement section.
2. Ensure that volute (Ref. No. 14) and casing cover (Ref. No.
6) are tted rmly (check fastener Ref. No. 15). Remove
spark plug wire from engine and turn engine over by pulling
the recoil starter. If engine does not turn freely, disassemble
pump and remove one shim.
NOTE: When adding or removing shims, it is best to proceed
with a 0.010” increment each time. If engine does turn freely,
add shims until it does strike, then remove a 0.010” shim. This
should allow proper clearance.
4-INCH TRASH PUMP
Figure 1 - Mechanical Seal
www.PumpAgents.com - Click here for Pricing/Ordering for Pumps and Parts
AMT Pumps 3993-Z6