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.

What you can use instead (for Craftsman 3902645)

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

Quick fit check: what “length” usually means

“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.

If you need…	Measure/confirm…	Why it matters
Hose/piping compatibility	Discharge outlet size and thread type	Prevents leaks and poor flow
Pumping capability	Vertical lift (head) and hose length	Determines real-world GPM
Safe operation	Voltage, amperage, grounding	Prevents nuisance trips and shock risk

Why it matters

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.

Ordering the right item

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.

Step-by-step: how we size a pump

• 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.).

What the 3902645 can do (from the manual)

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.

Discharge height above pumping level	Typical flow for 3902645 (GPM)
3 ft	26.0
5 ft	25.0
10 ft	21.5
15 ft	17.5
20 ft	11.0

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

Why it matters

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.

Quick sizing checklist before you buy or replace

• 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.

Ordering the right replacement

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).

The 7 major parts and what each one does

• 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.

How this applies to the Craftsman 3902645 submersible 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:

Component you will interact with	What it affects	Common symptom if restricted/damaged
Inlet screen	Water entry into the pump	Low or no flow, overheating risk
Discharge line/hose connection	Water exit path	Whipping hose, leaks, poor flow
Anti-airlock hole (in pump body)	Priming and preventing airlock	Pump runs but moves no water

Why it matters (troubleshooting and safe operation)

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.

Quick checks we recommend before assuming a “bad pump”

• 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.

Getting the right information and parts

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.

Quick conversion (HP to kW)

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)

Output kW vs input watts (why your numbers may not match)

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.

Generator sizing example from the Craftsman 3902645 manual

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

Motor HP	Approx. output kW	Minimum generator watts (manual)
1/6 HP	~0.12 kW	3000 W
1/4 HP	~0.19 kW	3200 W

Why it matters

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.

Helpful next steps

• 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.

Most common issues (and what they look like)

• 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.

Quick checks you can do safely

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.

Symptom-to-cause guide

Symptom	Most likely cause	What to do first
Runs, no water	Airlock	Clean anti-airlock hole; restart in 1/2 inch of water
Flow is weak	Screen restriction	Clean inlet screen; check hose for kinks
Stops and restarts	Thermal protector tripping	Check for low voltage, long cord, clog, or very low lift
Suddenly stops pumping	Water level too low, broken prime	Shut off immediately; remove remaining water with mop/squeegee

Why it matters

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