Craftsman 3902645 submersible pump Parts

The Craftsman submersible pump model 3902645 is not an SBC (Small Block Chevy) engine water pump, so the “SBC short water pump length” spec does not apply to this model. For pump-specific dimensions, we use the 3902645 documentation in the 3902645 owner's manual.

If you are trying to size or fit this submersible pump, these model-specific specs from the manual are the ones that matter most:

• Power: 115V, 60 Hz; use a 15-amp (or higher capacity) circuit
• Cord/grounding: 3-wire cord with grounding-type plug; do not remove the ground prong
• Max vertical discharge height: 20 ft (6 m) or less for model 3902645
• Low-water behavior: can pump down to about 3/16 in. of water (it will not remove all water)
• Anti-airlock hole: helps prime within about 15 seconds in as little as 1/2 in. of water

“SBC short water pump length” usually refers to the front-to-back engine pump dimension and shaft length for pulley alignment. A submersible utility/sump pump like the Craftsman 3902645 is sized differently.

Using an automotive “short water pump” dimension to select a submersible pump leads to the wrong part and poor performance. For the 3902645, matching head height, hose size, and electrical supply is what ensures proper drainage and prevents overheating from airlock or low-head overload.

We recommend matching by model number 3902645 and the pump diagram/part list for this unit. If you are shopping across models or categories, search by model number on Sears PartsDirect.

Last updated: February 2026

To size a water pump correctly, we match the pump’s flow (gallons per minute, GPM) to how much water you need to move, and the pump’s head (lift/pressure) to how high and how far you must push that water. For the Craftsman 3902645 submersible pump, the 3902645 owner's manual includes performance tables you can use to confirm fit.

• Estimate required flow (GPM): how fast water enters the pit or how fast you want to drain an area.
• Calculate total head (feet): vertical lift from the pumping water level up to the discharge point.
• Account for friction loss: longer hose runs, smaller hose diameter, and fittings reduce flow.
• Check the pump curve/table: confirm the pump still delivers enough GPM at your head.
• Confirm application limits: this model is a utility/sump style pump; it does not remove all water (it pumps down to about 3/16 in.).

The manual lists the 3902645 as 1/6 HP and provides GPM at different discharge heights. Use this as your quick reality check: if your required head is near the pump’s limit, flow drops sharply.

Head limit guidance: we size this model for a vertical discharge distance of 20 ft or less.

Correct sizing prevents common problems like slow draining, frequent cycling, and overheating. The manual notes the motor has an automatic resetting thermal protector; repeated trips point to overload causes such as very low head (low restriction), voltage issues, clogged impeller, or long extension cords.

• Measure vertical lift (feet) from water level to discharge outlet.
• Note hose diameter and length (garden hose vs sump/utility hose changes performance).
• Decide your target drain time (this sets your needed GPM).
• Plan for debris: keep the inlet screen clean.
• Avoid dry-running: keep at least 1/2 in. of water when restarting to protect the seal.

We recommend matching by model number 3902645 and your required head/flow. Start with the parts list for this model, or search by model on Sears PartsDirect to compare compatible pump parts and accessories.

Last updated: February 2026

For a typical water pump (including a Craftsman submersible pump like model 3902645), the 7 major parts are the motor, impeller, pump casing, shaft, bearings, mechanical seal(s), and the inlet/outlet connections. These parts work together to move water while keeping the motor area sealed and leak-free (see the 3902645 owner's manual).

• Motor: provides the power to spin the pump.
• Impeller: the rotating vanes that push water through the pump.
• Pump casing (volute/housing): directs water flow and contains the impeller.
• Shaft: transfers motor rotation to the impeller.
• Bearings: support the shaft so it spins smoothly.
• Mechanical seal(s): helps prevent water from leaking into areas it should not.
• Inlet and outlet (ports/connections): where water enters and exits the pump.

Submersible pumps package these components tightly and rely on sealing to protect the motor. For the 3902645, the manual also calls out items that function like “major components” in day-to-day use:

Knowing the major parts helps you diagnose symptoms faster and avoid damage. For example, an airlock can make the pump run without moving water, which can overheat the unit; keeping the inlet screen and anti-airlock hole clear helps the impeller and casing do their job.

• Unplug power before inspecting or servicing.
• Confirm the water level is high enough for operation.
• Check the inlet screen for debris.
• If it runs but does not pump, clear the anti-airlock hole carefully.
• Inspect the discharge hose/connection for kinks or blockage.
• If the unit suddenly stops pumping, shut it off immediately and re-check water level.

Use the parts list for Craftsman 3902645 on this model page when available; for broader model lookups and ordering by model number, use Sears PartsDirect.

Last updated: February 2026

A 0.5 HP water pump is about 0.37 kW (since 1 HP is approximately 0.746 kW). For your Craftsman 3902645 submersible pump, the manual lists it as 1/6 HP, which is about 0.12 kW (motor output), not 0.5 HP; see the owner's manual.

Use this formula for motor output power:

• kW = HP × 0.746
• 0.5 HP × 0.746 = 0.373 kW (commonly rounded to 0.37 kW)
• 1/6 HP (0.1667) × 0.746 = 0.124 kW (about 0.12 kW)

A pump motor draws more electrical power than it delivers as HP because of efficiency and startup surge.

• kW (from HP) is the motor’s mechanical output rating.
• Input watts are what your outlet or generator must supply.
• Small pump motors can have high starting (surge) watts, especially at startup.

The manual provides generator minimum watt ratings for similar pump motors:

Using the right kW and watt ratings helps prevent nuisance tripping, overheating, and low-voltage issues. This is especially important with extension cords, generators, and 115-volt single-phase pumps like the Craftsman 3902645.

• Confirm the pump’s HP rating on the nameplate (it should match the manual’s 1/6 HP for model 3902645).
• If you are sizing a generator, use the manual’s minimum watt guidance and add any other loads.
• Follow the manual’s electrical safety guidance (grounded 3-prong outlet, unplug before servicing).
• If the pump runs but does not move water, check for an airlock and clean the anti-airlock hole as described in the manual.
• For parts lookup by model number, start with the model parts list, or search by model on Sears PartsDirect.

Last updated: February 2026

For the Craftsman 3902645 submersible pump, the most common problem we see is the pump running but not moving water because of an airlock or a restriction at the inlet screen. Running the pump with too little water (running dry) is also a frequent cause of seal damage and overheating; both issues are covered in the owner's manual.

• Airlock: Motor runs, little or no water discharges.
• Clogged inlet screen or impeller area: Reduced flow, intermittent pumping.
• Low water level or broken prime: Pump was working, then discharge suddenly stops.
• Thermal overload cycling: Pump shuts off, then restarts after cooling.
• Electrical supply problems: Low voltage or long extension cords can cause overheating and cycling.

1. Disconnect power before touching the pump or discharge line.
2. Confirm water depth: Keep the pump in at least 1/2 inch of water before restarting; the shaft seal needs water for lubrication.
3. Check for an airlock: Clean the anti-airlock hole (a paper clip or small wire works) so the pump can prime.
4. Inspect the inlet screen: Remove debris and confirm the screen is clear.
5. Verify the discharge hose: Make sure it is secured and not kinked or blocked.

Airlocks and running dry can overheat the pump and damage the shaft seal. Keeping the inlet screen clean and maintaining proper water level helps prevent nuisance shutdowns and early pump failure.

You can also search model-specific diagrams and replacement items by model number on Sears PartsDirect.

Last updated: February 2026